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Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations (1996)

Chapter: 13 Effects of Cold and altitude on Vitamin and Mineral Requirements

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Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

13
Effects of Cold and Altitude on Vitamin and Mineral Requirements

Robert D. Reynolds1

INTRODUCTION

The importance of adequate caloric and fluid intake must be rated at least as highly as that of oxygen

(Pugh, 1965, p. 314).

Although Pugh limited his statement about the importance of nutrition at high altitudes to that of energy and fluids, the same concept can be extended to all of the nutrients. However, a superficial perusal of the published literature on the effects of altitude demonstrates that the preponderance of research efforts has been directed to understanding the impact of a limited oxygen supply on human performance. With respect to nutrition, there has been only a modest effort to determine energy intake and to determine the preferred mix of energy derived from carbohydrate, fat, and protein. Unfortunately, a paucity of efforts has been expended to determine the effects of cold and altitude on vitamin and mineral requirements even though these micronutrients are absolutely essential in converting the food consumed into the energy that is

1  

Robert D. Reynolds, Department of Human Nutrition and Dietetics, The University of Illinois at Chicago, Chicago, IL 60612-7256

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

required to function in these extreme conditions. These micronutrients are no less important than is oxygen. It just takes longer to become deficient in them than it does for oxygen.

In the past, U.S. Army recommendations regarding micronutrient intake for work in cold and high-altitude environments have been limited to three areas of consideration. They have suggested the need for increased requirements for vitamins and minerals to accommodate the caloric requirement of cold and high-altitude operations; a high altitude-induced increase in the requirement for vitamins A, E, and C, specifically; and the need for caution in the use of vitamin and mineral supplements to attempt to prevent cold stress (Thomas et al., 1993a, b; Askew, 1989). However, increased intakes have not been recommended.

Under any environmental condition, it is necessary to measure accurately intake, excretion, and several indices of status to determine nutrient requirements. A complete set of these indices has not been measured for any of the vitamins or minerals for persons living or working in the cold or at high altitudes. Therefore, it is not possible to report here the actual requirements for any of these micronutrients as affected by prolonged exposure to cold or high-altitude environments.

The approach used in this chapter will be to present a short statement on the major role of each vitamin and mineral in human metabolism, followed by a review of reported dietary intakes or status in various populations living or working in cold climates or at moderate to high altitudes. Finally, for each vitamin and mineral, a micronutrient intake goal will be suggested and compared to the current Recommended Dietary Allowance (RDA) (NRC, 1989), the Military Recommended Dietary Allowance (MRDA) (AR 40-25, 1985), and the anticipated intake of each nutrient provided by the Ration, Cold Weather (RCW) as formulated by the U.S. military. Each micronutrient intake goal has been derived by the author from a systematic reading of the relevant published literature and from personal consideration of widely-accepted, general nutrition principles.

Construction of the micronutrient intake goals assumes that the individuals using it are in generally good health and nutrient status prior to beginning the expedition or maneuver. Thus, the aim of the micronutrient intake goals is to keep the individuals healthy rather than to make them healthy. Construction of the micronutrient intake goals should not be constrained by the limitations of the micronutrient availability from foods in the amount normally consumed. Therefore, use of the terms dietary or dietary intake as they relate to the micronutrient intake goals are not necessarily appropriate.

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

ESTIMATED ENERGY INTAKES

Many of the nutrients, especially the B vitamins, are involved with the production of energy via numerous steps in the Krebs citric acid cycle. Thus, consideration will be given in the construction of the micronutrient intake goal to the estimated intakes of total food energy by those persons engaged in strenuous work in the cold or at high altitudes.

It has been estimated that in the cold, the average energy consumption by U.S. military soldiers who self-selected foods from the RCW was 2,800 kcal/d, and from the Meal, Ready-to-Eat (four meals) was 3,000 kcal/d (Personal communication, R. W. Hoyt, U.S. Army Research Institute of Environmental Medicine, Natick, Mass., 1994). The current MRDA for energy in cold weather is 4,500 kcal/d (AR 40-25, 1985). Jones and Lee (see Chapter 11 in this volume) estimate that energy requirements (expenditure) for soldiers range between 4,200 and 5,000 kcal/d during periods of physical exertion in the cold. The negative difference between energy intakes and expenditures thereby results in loss of body weight.

During the conduct of Operation Everest II with simulated altitudes up to 8,848 m (29,000 ft), subjects consumed between 2,500 and 3,000 kcal/d, with 45 percent of the energy being provided by carbohydrates (Rose et al., 1987). Estimates of energy expenditure between 4,000 and 5,000 kcal/d have been reported for those engaged in strenuous exertion while at high altitudes (Reynolds et al., 1992). Therefore, for the construction of the micronutrient intake goal, an estimated average energy intake of 4,500 kcal/d will be assumed in order to keep the personnel in energy balance. Any deficit between energy intake and expenditure must result in loss of body tissue.

FAT-SOLUBLE VITAMINS

Vitamin A
Functions

Vitamin A is essential for the visual process, differentiation of epithelial cells, maintenance of the immune system, and integrity of the skin. The normal needs for vitamin A can be met by consumption of either preformed vitamin A or β-carotene, with the latter having a considerably lower toxicity (NRC, 1989).

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×
Intake and Status

Of the fat-soluble vitamins, vitamin A has caused the most problems for polar explorers. Shearman (1978) presented a graphic description of vitamin A toxicity experienced by members of the three-man, 1912–1913 Mawson Australian Antarctic expedition, in which two men died, with only Sir Douglas Mawson surviving. Early in the expedition, Lt. Ninnis and one of the sleds loaded with most of the food fell into a crevasse and disappeared. Over the next 23 days, Xavier Mertz and Mawson were forced to reduce their daily food intake from the normal 34 oz (971 g) to 14 oz (400 g), much of which was dog meat that became available as each dog died (Mawson, 1915). As Mawson reported in his journal, ''It was a happy relief when the liver appeared; even if little else could be said for its flavor, it was easily chewed and demolished" (Shearman, 1978 quoting Mawson, 1915, p. 284).

Over a 9-d period, Mertz's health rapidly deteriorated, culminating in his death, with intervening severe bouts of dysentery, fecal incontinence, depression, delirium, peeling skin, and loss of hair—all symptoms characteristic of acute vitamin A toxicity. Shearman (1978) estimated that as little as 100 g of husky dog liver could contain upwards of 1,000,000 international units (IU) (300,000 µg retinol equivalents [RE]) of vitamin A, which was sufficient to cause the toxic symptoms experienced by Mertz.

This was not the only polar expedition that was thwarted by hypervitaminosis A. Today, with knowledge of the potential vitamin A toxicity from consumption of dog, seal, polar bear, or reindeer liver (Shearman, 1978), polar explorers or workers are unlikely to repeat such experiences, but warnings must still be given to those planning to spend long periods of time under such environmental conditions.

Sundaresan and Therriault (1969) studied rats chronically exposed to air temperatures of 5°C (41°F) and observed that the total liver levels of retinol did not differ from rats maintained at 25°C (77°F). Rats kept at 5° or 25°C (41° or 77°F) were injected daily with one of six different levels of retinoic acid. Thirty-day survival was used as the marker for adequacy of retinoic acid. At 5°C (41°F), at least 100 µg retinoic acid daily was necessary for survival and growth, whereas only 5 µg retinoic acid was required daily for survival and growth at 25°C (77°F). From this, they concluded that cold-adapted rats required a 20-fold greater intake of vitamin A than did their room temperature-acclimatized counterparts. Lui and Roels (1980) reported that vitamin A deficiency did not affect energy production by the Krebs cycle, but glycogen synthesis from lactate and glycerol appeared to be slowed down. Thus, restoration of depleted energy stores may be impaired by a severe deficiency of this vitamin.

Draper (1976) reported that Norwegian and Finnish Lapps (a race of formerly nomadic people residing in Northern Scandinavia) consume upwards of 50,000 to 62,000 IU of vitamin A (15,000 to 18,600 µg RE) per day,

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

usually in the form of reindeer liver. Hasunen and Pekkarinen (1976) also reported that Finnish Skolt (a subpopulation of the Lapps) children consumed amounts of vitamin A well in excess (two- to fourfold) of the RDA. Rodahl and Issekutz (1965) reported that Alaskan Eskimos consumed approximately twice as much vitamin A as did U.S. Army or Air Force personnel living under similar conditions (3,750 versus 1,900 µg RE, respectively, or 3.6- and 1.9-fold higher than the RDA, respectively). Thus, indigenous persons living in the higher latitudes of the world continue to demonstrate comparatively high dietary intake of vitamin A.

Compared to the 1989 RDA (NRC, 1989), it was reported that subjects in the 38-d Operation Everest II consumed increased amounts of vitamin A (Rose et al., 1987) as did subjects during an exercise at 3,500 to 4,050 m (11,475 to 13,279 ft) altitude in Bolivia (Edwards et al., 1991). However, Hannon et al. (1976) reported a transient reduction in the consumption of vitamin A by eight women during a sojourn to 4,300 m (14,098 ft) altitude. In addition to a decreased intake, it has been suggested that a malabsorption of fat may occur at high altitudes (Boyer and Blume, 1984; Ward et al., 1989b). This interpretation of the data has been criticized because two of the three subjects were reported to have been fat malabsorbers at sea level altitude prior to the experiment. Thus, it is not known whether impaired intestinal fat absorption occurs at high altitude, and if it does, whether it would be sufficient to affect absorption of the fat-soluble vitamins.

Author's Recommendation

Caution is recommended regarding the consumption of even modest supplements of vitamin A by persons working in cold or high-altitude environments due to the mobilization and utilization of body fat that often occurs under these circumstances and the resultant release of vitamin A stores into the circulation.

It has been reported that 6 months to 2 years is required for a person consuming a vitamin A-deficient diet to become deficient. Thus, there is little justification to recommend intakes of vitamin A above RDA or MRDA levels because most expeditions or maneuvers are of a much shorter duration than the time required to become deficient. Deficiency of the vitamin is initially characterized by a reduction in night vision and dark adaptation, symptoms that are readily noticed by the person involved. Only under such instances of suspected vitamin A deficiency should a supplemental regimen of no more than the current RDA of 1,000 µg RE (NRC, 1989) be considered. Administration of supplemental vitamin A to a person with an adequate vitamin A status does not improve night vision further. Therefore, the suggested micronutrient intake goal for vitamin A is set at the RDA and MRDA level of 1,000 µg RE (Table 13-1). This recommendation is in contrast to the Thomas et al. (1993b)

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

TABLE 13-1 Suggested Micronutrient Intake Goal for Use in the Cold and at High Altitudes

Nutrient

Micronutrient Intake Goal*

RDA

MRDA

RCW

as provided§

RCW

as consumed ||

Fat-soluble vitamins

 

 

 

 

 

Vitamin A (µg RE)

1,000

1,000

1,000

8,022

6,016

Vitamin D (µg)

10

10

Vitamin E (mg α-RE)

400

10

10

21

15.8

Vitamin K (µg)

70–80

70–80

Water-soluble vitamins

 

 

 

 

 

Thiamin (mg)

3

1.5

1.6

5.7

4.3

Niacin (mg)

20

19

21

31

23.2

Riboflavin (mg)

3

1.7

1.9

2.6

1.9

Vitamin B6 (mg)

2

2

2.2

3.9

2.9

Vitamin B12 (mg)

3

2

3

0.8

0.6

Pantothenic acid# (mg)

10

4–7

Biotin# (µg)

30–100

30–100

Folic acid (µg)

400

200

400

141

106

Vitamin C (mg)

250

60

60

329

247

Minerals

 

 

 

 

 

Calcium (mg)

800–1,200

800–1,200

800–1,200

1,379

1,034

Phosphorus (mg)

800–1,200

800–1,200

800–1,200

2,168

1,626

Magnesium (mg)

400

350

350–400

529

444

Iron (mg)

15–20**

10

10–18

19

14

Zinc (mg)

20

15

15

10.8

8.1

Copper# (mg)

1.5–3

1.5–3

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

NOTE: RE, retinol equivalents; α-TE, α-tocopherol equivalents.

* As recommended by the author.

Recommended Dietary Allowance for males aged 19–24 and 25–50 (NRC, 1989).

Military Recommended Dietary Allowance (AR 40-25, 1985).

§ Micronutrient content of the Ration, Cold Weather (RCW).

|| Average intake of nutrients contained in the RCW, assuming an average of 75 percent consumption of the contents (see Hoyt and Honig, Chapter 20 in this volume).

# Estimated Safe and Adequate Daily Dietary Intake (NRC, 1989).

** 15 mg suggested for men, and 20 mg suggested for women.

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

suggestion that "…the body's need for vitamin A…may increase at altitude" (p. 36).

Whereas β-carotene does not share the toxicity that preformed vitamin A does, there is no RDA or MRDA for this provitamin. Should supplemental amounts of vitamin A be found to be beneficial as a result of future research in this area, thought should be given to supplementing with β-carotene rather than with vitamin A.

Vitamin D
Functions

Vitamin D is important for the absorption and metabolism of calcium and phosphorus. Other roles for this vitamin have recently been elucidated (Suda et al., 1990), but they do not appear to be pertinent to the present discussion.

Intake and Status

Due to the synthesis of previtamin D3 from 7-dehydrocholesterol during exposure of the skin to ultraviolet irradiation, it is unlikely that a person operating in the cold or at high altitudes would develop a vitamin D deficiency, unless a prolonged expedition occurred during the long polar nights. Even though the sunlight is very oblique at the polar latitudes, the direct solar radiation on the face and any other exposed skin, along with the reflected radiation from the ice and snow, should be adequate to synthesize sufficient vitamin D3 to meet the nutritional needs of the explorer. High altitudes generally lie at more moderate latitudes with the result of more direct solar radiation. Thus more direct exposure, in addition to increased intensity of the radiation due to the decrease in absorption of ultraviolet rays by the thinner atmosphere, should result in sufficient exposure to ultraviolet irradiation for synthesis of adequate amounts of vitamin D to meet nutritional and functional needs.

Author's Recommendation

The exposure of the skin to ultraviolet radiation, coupled with a possible release of vitamin D stores from mobilization and utilization of fat stores during prolonged and strenuous physical exertion coupled with inadequate energy intake, should provide sufficient vitamin D to meet nutritional needs in both cold and high-altitude environments. In addition to sunlight, the inclusion of vitamin D-supplemented milk powder in the diet should provide

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

sufficient vitamin D to meet nutritional needs. Thus, the suggested micronutrient intake goal for vitamin D is set at the RDA level of 10 µg (Table 13-1).

Vitamin E

Simon-Schnass (see Chapter 21 in this volume) reviews and discusses the literature on vitamin E; therefore, a short comment on another consideration of vitamin E supplementation is included here.

Author's Recommendation

Due to the reduction or prevention of oxidation of fatty acids by vitamin E, it is theoretically possible that supplementation with the vitamin could increase the oxygen supply for such purposes as energy production by the Krebs cycle (Williams, 1989). In addition to the beneficial effects of 400 µg/d vitamin E discussed by Simon-Schnass (see Chapter 21 in this volume), consideration should be given to the powerful epidemiological data recently reported by Stampfer et al. (1993) and Rimm et al. (1993), which demonstrated that consumption of 200 mg or more of vitamin E per day for periods of at least 2 years resulted in a significant reduction in the incidence of heart attacks. Due to the unknown etiology of high-altitude cerebral or pulmonary edema (HACE and HAPE, respectively), consideration should be given to instituting a regimen of elevated vitamin E intakes for substantial periods of time prior to exposure to high altitudes, as well as maintaining this level of intake during exposure to altitude. In view of the extremely low toxicity of vitamin E, this regimen may result in a reduction in either the incidence or severity of HACE and HAPE, both deadly consequences of working at high altitudes. Maintenance of membrane fluidity in a cold environment by supplemental vitamin E also supports such a supplemental regimen for this vitamin (see Simon-Schnass, Chapter 21 in this volume). For these reasons, the suggested micronutrient intake goal for vitamin E is set at 400 mg α-tocopherol equivalents (α-TE) (Table 13-1).

Vitamin K
Functions

Vitamin K functions as a cofactor for several enzymes that modify and activate a number of blood clotting factors (NRC, 1989). Deficiency of the vitamin results in hemorrhages, whereas toxicity from intake of large doses is rare (NRC, 1989). Intestinal microbial synthesis also serves as a source of the vitamin (NRC, 1989).

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×
Status and Intake

There are no known data on either changes in dietary intake or changes in status of this vitamin as a result of exposure to cold or high altitudes.

Author's Recommendation

A long period of time is required to produce deficiency in vitamin K. In addition, the vitamin is synthesized intestinally. Hence, it is suggested that the micronutrient intake goal for vitamin K be set at the RDA level of 70 to 80 µg, which is commensurate with what is found normally in foods.

WATER-SOLUBLE VITAMINS

All of the water-soluble vitamins, with the exception of folic acid and vitamin C, are intimately involved in the oxidation and conversion of food to energy at multiple steps leading up to and in the functioning of the Krebs cycle (see Hunt and Groff, 1990). Thus, an adequate nutritional status with respect to the water-soluble vitamins is essential for the production of sufficient energy for thermogenesis and for physical exertion while in the cold and at high altitudes.

Thiamin
Functions

Thiamin is essential for energy metabolism; it serves as a cofactor in the oxidative decarboxylation of pyruvate to acetylcoenzyme A (acetyl-CoA) immediately prior to its entrance into the Krebs cycle, in the conversion of α-ketoglutarate to succinylcoezyme A (succinyl-CoA) in the Krebs cycle with subsequent oxidation to adenosine triphosphate (ATP), and in the hexose monophosphate shunt. If the thiamin supply is insufficient, the increased demand for acetyl-CoA during physical activity or for thermogenesis may not be met. As a result, more pyruvate will be converted to lactate with subsequent early onset of fatigue (Williams, 1989).

Intake and Status

Draper (1976) reported that inadequate intake of thiamin was one of the primary dietary deficiencies among Norwegian Lapps. Hasunen and Pekkarinen

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

(1976) reported a similar observation among Finnish Skolt children. Hannon et al. (1976) reported a transient reduction of thiamin intake by women during their sojourn to 4,300 m (14,098 ft). However, there was an increased intake during Operation Everest II (Rose et al., 1987) and during the military exercise in Bolivia (Edwards et al., 1991). It has been suggested that 10 to 14 days are required for consumption of a thiamin-deficient diet to result in the appearance of deficiency symptoms.

Author's Recommendation

Due to thiamin's role in the metabolism of carbohydrate, the RDA for thiamin is based on total anticipated energy intake from carbohydrate and some amino acids (NRC, 1989). There have been many reports of increased intake of carbohydrate, at the expense of fat intake, at high altitudes (Frisancho, 1981; Ward et al., 1989b). Thus, the suggested micronutrient intake goal of this vitamin for those working either in the cold or at high altitudes is set at 3 mg, which is twice the existing RDA of 1.5 mg/d and higher than the MRDA of 1.6 mg/d. The suggested micronutrient intake goal of 3 mg/d is a prudent dose considering the low toxicity (NRC, 1989) of this vitamin.

Niacin
Functions

Niacin as nicotinamide adenine dinucleotide (NAD) functions mainly to produce ATP from glycolysis and from the Krebs cycle. It is also necessary for the conversion of pyruvate to acetyl-CoA, in the hexose monophosphate shunt, and in the synthesis of fatty acids from acetyl-CoA. A deficiency of niacin could impair glycolysis and the Krebs cycle, whereas excessive niacin supplementation may suppress the release of free fatty acids from adipose tissue through decreased lipolysis, resulting in a decreased availability of a major fuel source for utilization during strenuous exercise (Bulow, 1981; Carlson et al., 1963). Thus, if muscle glycogen levels are low, as may occur during prolonged physical exertion in the cold or at altitude, excessive niacin supplements could actually impair physical performance (Williams, 1989).

Intake and Status

An increase in niacin intake was reported among participants in Operation Everest II (Rose et al., 1987) during their simulated exposure to high altitudes and by U.S. Army soldiers during the exercise in Bolivia (Edwards et al.,

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

1991). However, Hannon et al. (1976) reported a reduced intake by women during a sojourn to 4,300 m (14,098 ft) altitude. Niacin status was not determined in any of these studies.

Author's Recommendation

A niacin deficiency severe enough to impair glycolysis is difficult to produce due to the normal formation of niacin from tryptophan, a pathway that produces approximately half as much niacin as that provided by dietary sources alone (NRC, 1989). Thus, due to the inhibition of release of free fatty acids, it appears that an oversupply of the vitamin might be more critical than an undersupply. For this reason, the suggested micronutrient intake goal for niacin is set at 20 mg/d, which is between the RDA and the MRDA (Table 13-1). This amount should be sufficient to prevent a deficiency of the vitamin but not so high as to inhibit release of fatty acids.

Riboflavin
Functions

Riboflavin, as flavin adenine dinucleotide (FAD), is essential for electron transport, which is needed for the conversion of fatty acids to acetyl-CoA and for the conversion of succinate to fumarate in the Krebs cycle (NRC, 1989).

Intake and Status

The U.S. Army reported an increase in the intake of riboflavin by soldiers working at 3,500 to 4,050 m (11,475 to 13,279 ft) in Bolivia (Edwards et al., 1991) and during Operation Everest II (Rose et al., 1987), whereas Hannon et al. (1976) reported a decreased intake of riboflavin by women during a sojourn to 4,300 m (14,098 ft) altitude. The major source of dietary riboflavin is from dairy products, which may be limited during prolonged expeditions and may have been limited during the study reported by Hannon et al. (1976). Strict vegans who consume no meat or dairy products may be at risk for developing a riboflavin deficiency under these environmental conditions (Cooperman and Lopez, 1991). A riboflavin-deficient diet must be consumed for 2 to 6 weeks before deficiency symptoms begin to appear.

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×
Author's Recommendation

Due to the low toxicity, the essentiality for energy production, and the need for increased food intake during prolonged expeditions in the cold or at altitudes, it is suggested that the micronutrient intake goal for riboflavin be set at 2.5 mg/d, which is slightly higher than either the RDA or the MRDA.

Vitamin B6
Functions

Vitamin B6 is a required cofactor for glycogen phosphorylase, which converts stored glycogen into glucose, and is essential for the conversion of various amino acids into oxaloacetate as well as the conversion of α-ketoglutarate, succinyl-CoA, and pyruvate into various amino acids (NRC, 1989). Thus, a pronounced deficiency of vitamin B6 would cause a decrease in the conversion of glycogen into glucose, depleting a major source of fuel (Leklem, 1991). The onset of deficiency may be as short as 2 to 4 weeks.

In addition to its role in glycogen and amino acid metabolism, two of the major forms of vitamin B6, pyridoxal 5'-phosphate (PLP) and pyridoxal (PL), appear to affect the erythrocyte hemoglobin oxygen binding affinity (Reynolds and Natta, 1985), with PLP reducing the binding affinity and PL increasing the affinity. These effects, observed thus far only in vitro and not yet confirmed in vivo, could have the effect at high altitudes of either lowering the ability of hemoglobin to bind sufficient oxygen in the lungs or of increasing the binding affinity to such an extent that release of the bound oxygen in the peripheral capillary beds is diminished. Either scenario could have serious adverse consequences.

Intake and Status

Deuster et al. (1992) reported that consumption of commercially available dehydrated rations for 31 days provided amounts of vitamin B6 at or above the RDA, and that physical operations at altitudes of 2,400 to 4,300 m (7,869 to 14,098 ft) did not appear to affect vitamin B6 status, as determined by concentrations of PLP in serum and erythrocytes. There was an increased intake of vitamin B6 during Operation Everest II (Rose et al., 1987). However, there was a reduced intake of this vitamin by soldiers during their exercise in Bolivia (Edwards et al., 1991).

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×
Author's Recommendation

There are no known endurance or performance benefits in the cold or at high altitudes from supplementation of otherwise well-nourished individuals with extra doses of vitamin B6. Due to the unknown effects of supplemental vitamin B6 on hemoglobin oxygen binding affinity, no increased intakes of vitamin B6 above RDA or MRDA levels have been included in the suggested micronutrient intake goal (Table 13-1).

Vitamin B12
Functions

Vitamin B12 is needed for the conversion of methylmalonyl-CoA into succinyl-CoA, which enters directly into the Krebs cycle. Vitamin B12 is also essential for normal cell division.

Intake and Status

An increase was reported in the intake of vitamin B12 during Operation Everest II (Rose et al., 1987) and by soldiers working in Bolivia (Edwards et al., 1991). There are no known reports of changes in vitamin B12 status among persons living or working in the cold or at high altitude.

Author's Recommendation

Due to the prolonged period of time (5 to 10 years) required to develop a deficiency of vitamin B12 (Ellenbogen and Cooper, 1991), it is unlikely that supplementation with this vitamin would be of benefit except for strict vegans who are already at risk for deficiency. Consumption of any fermented food, such as soy sauce or tofu, provides sufficient vitamin B12 to meet anticipated needs in the cold or at altitude (Nutritionist IV, 1993). Three µg of vitamin B12, equivalent to the MRDA, has been included in the suggested micronutrient intake goal (Table 13-1) due to the relatively high incidence of vegetarianism among civilian mountain climbers.

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×
Pantothenic Acid
Functions

Pantothenic acid is part of the coenzyme A molecule, which is involved in the oxidation of pyruvate to acetyl-CoA, the conversion of α-ketoglutarate to succinyl-CoA in the Krebs cycle, as well as the metabolism of fatty acids. A deficiency in this vitamin (and thus a deficiency of coenzyme A) may decrease the availability of substrate for the Krebs cycle, thereby shifting energy production to the less-efficient anaerobic glycolysis pathway.

Intake and Status

Nice et al. (1984) reported that supplementation with 1 g pantothenate daily for 2 weeks had no effect on a treadmill run to exhaustion. There are no known reports of either intake or changes in pantothenate status of persons living or working in the cold or at high altitude.

Author's Recommendation

It has been estimated that 4 to 10 days is required for the development of a pantothenic acid deficiency. Due to the low toxicity of this vitamin (NRC, 1989) and due to its essentiality in energy production, 10 mg of pantothenic acid per day is recommended in the suggested micronutrient intake goal (Table 13-1). This is somewhat above the Estimated Safe and Adequate Daily Dietary Intake (ESADDI) (NRC, 1989) level of 4 to 7 mg/d.

Biotin
Functions

Biotin is essential for the conversion of pyruvate into oxaloacetate, the conversion of acetyl-CoA into fatty acids, and the conversion of propionyl-CoA into methylmalonyl-CoA prior to its entrance into the Krebs cycle (NRC, 1989).

Intake and Status

It is difficult to induce deficiency of biotin unless one consumes excessive amounts of raw egg whites, which contain avidin, an irreversible binder of

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

biotin (NRC, 1989). There are no known reports on intake or changes in biotin status of persons living or working in the cold or at high altitude.

Author's Recommendation

Due to the widespread distribution of biotin in foods (Bonjour, 1991) and to the difficulty of inducing a deficiency (NRC, 1989), there is no justification to set the suggested micronutrient intake goal for biotin above the ESADDI of 30 to 100 mg/d (Table 13-1).

Folic Acid
Function

Although not involved in the production of energy, folic acid is essential in the formation of hemoglobin and in methyl transfer involved in cell division (NRC, 1989). It has been estimated that it takes 3 to 4 months of consumption of a folate-deficient diet is required before deficiency symptoms begin to appear. The major dietary source of folic acid is leafy green vegetables (Brody, 1991), which are notoriously scarce on expeditions in the cold or at high altitude.

Intake and Status

Draper (1976) reported that Canadian Eskimos had low serum levels of folate, usually without signs of any hematological problems. This apparent deficiency may be the result of a low consumption of leafy green vegetables by persons living in these geographical areas. Intake of folic acid was reported to be increased during Operation Everest II (Rose et al., 1987) but decreased during the military exercise in Bolivia (Edwards et al., 1991).

Author's Recommendation

Concern exists about the ability of folic acid oversupplementation to mask symptoms of pernicious anemia, particularly in the elderly. Pernicious anemia is caused by decreased absorption or inadequate intake of vitamin B12. It is suggested that the micronutrient intake goal for folic acid be set at 400 µg/d (Table 13-1). This level should provide sufficient folic acid to women of childbearing age to reduce the incidence of neural tube defects in their children (Czeizel, 1993). It is important, however, that this level of folic acid be made

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

available in the foods actually consumed in the cold or at high altitudes due to the lack of fresh leafy green vegetables in the normal diet in these environments.

Vitamin C
Functions

Vitamin C facilitates the intestinal absorption of nonheme iron, is involved in the formation of collagen, and is needed for proper adrenal function (NRC, 1989). A deficiency of the vitamin (intakes of 10 to 20 mg/d) results in scurvy, which is characterized by sore gums, painful joints, and multiple hemorrhages, leading ultimately to an excruciatingly painful death (Friedrich, 1988). Like folic acid, vitamin C is one of the few water-soluble vitamins that is not required for the production of energy. The role of large supplemental doses in enhancing the immune system (Pauling, 1970) is controversial at present.

Intake and Status

Scurvy was prevalent on many of the early polar expeditions. It is possible that as many expeditions failed due to vitamin C deficiency as due to vitamin A toxicity. Only after the discovery by Lind in 1753 of the preventive action of lemons were there opportunities for extended travel to the far northern and southern latitudes for prolonged periods of time without fear of this painful and deadly disease. In 1850, a successful arctic expedition carried lemons. However, other expeditions, such as Sir George Nare's expedition to the North Pole, may have failed due to inclusion of limes rather than lemons as antiscorbutics because limes contain only half the amount of vitamin C of lemons (Nutritionist IV, 1993). It is also likely that the 1913 Scott expedition to Antarctica failed due to the absence of any antiscorbutics (Friedrich, 1988). Thus, vitamin C has a long and colorful linkage with early polar expeditions.

More recently, Draper (1976) reported low dietary intakes of vitamin C by Norwegian Lapps, low plasma levels of vitamin C in the Chukchi people of Siberia, and clinical signs of scurvy in Eskimos in four northern Canadian settlements. Hasunen and Pekkarinen (1976) reported daily dietary intakes of only 17 to 34 mg of vitamin C by Finnish Skolt children. Similarly, Rodahl and Issekutz (1965) reported that adult Alaskan Eskimos consumed only about 28 mg of vitamin C per day. Petrásek (1978) described several Russian studies in which there appeared to be a …considerable vitamin C deficiency in polar explorers on an intake of 100 mg/day…'' (p. 509). LeBlanc (1975) reported a low blood level of vitamin C in persons living at Fort Churchill, Manitoba, with the concentration being lower in March than in August. There was an

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

increased intake of vitamin C during Operation Everest II (Rose et al., 1987) and during an exercise in Bolivia (Edwards et al., 1991), but a reduced intake by women during a sojourn to 4,300 m (14,098 ft) (Hannon et al., 1976).

Margaria et al. (1964) administered an acute dose of 250 mg of vitamin C approximately 90 minutes prior to a treadmill run to exhaustion, with no significant beneficial effects of supplementation. Numerous other studies also failed to observe any performance benefit during prolonged exertion from intake of supplemental vitamin C.

LeBlanc (1975) reported that daily supplementation of 407 of the previously mentioned northern Manitoba inhabitants with 1 g of vitamin C during the winter months did not reduce the number of colds per subject or the days of symptoms per subject, but did significantly reduce the number of days they were confined to their houses (p < 0.001) when compared to a similar group of 411 control inhabitants who received a placebo. Thérien et al. (1949) showed that supplementation of monkeys with 325 mg of vitamin C per day or humans with 525 mg of vitamin C per day significantly blunted the fall in muscle, rectal, or skin temperatures following exposure to cold air, compared to comparable subjects supplemented with only 25 mg of vitamin C per day. Whereas the actual mean surface or tissue temperature differences were less than 1°C (34°F), this difference may be sufficient in some circumstances to mean the difference between life or death.

With the intake of vitamin C maintained at 91 mg/d, Boutwell et al. (1950) reported a decreased urinary excretion of ascorbic acid when subjects were repeatedly exposed to simulated altitudes of 5,450 m (17,869 ft). They attributed this decrease to an increased utilization of the vitamin because the excretion was also reduced during the intervening periods at low altitudes as well as during the simulated exposures to high altitude.

Mitchell and Edman (1951) reviewed much of the early literature on vitamin C and climatic stress. They reported a decrease in adrenal concentrations of vitamin C in guinea pigs that were exposed to simulated high altitudes.

Recently, Schwartz and Weiss (1994) reported a significant positive correlation between vitamin C intake and forced expiratory volume in 1 second, corrected for body size (FEV1). Dividing subjects into tertiles based on vitamin C intake from all sources (food plus supplements), persons who were consuming an average of 17 mg of vitamin C per day had an FEV1 of approximately 2,530 ml, those consuming an average of 66 mg of vitamin C per day had an FEV1 of approximately 2,550 ml, and those consuming an average of 178 mg of vitamin C per day had an FEV1 of approximately 2,570 ml (Schwartz and Weiss, 1994). Data were derived from the First National Health and Nutrition Examination Survey, with the total number of subjects being 2,384. Peters et al. (1993) reported that supplementation of ultramarathon runners with 600 mg of vitamin C per day for 3 weeks prior to a race resulted in a significantly lower number of upper respiratory tract infections

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

compared to those taking a placebo. This conclusion, however, has been challenged (Gershoff, 1994; Peters and Noakes 1994). Nevertheless, it is possible that supplemental vitamin C may have protective or beneficial effects on the pulmonary as well as the immunological systems for those engaged in strenuous physical exertion such as occurs when working at high altitudes or in the cold.

Author's Recommendation

Due to the relatively low toxicity of vitamin C, the role of vitamin C in the synthesis of adrenal hormones, its possible role in maintaining core and surface body temperature, its apparent beneficial effects in pulmonary function, and its possible role in maintaining immune function, it is suggested that the micronutrient intake goal be set at 250 mg/d for prolonged expeditions or maneuvers in cold or high-altitude environments (Table 13-1). This recommendation is considerably above the RDA and the MRDA of 60 mg/d. However, this suggested level of intake is commensurate with that already provided in the RCW as reportedly eaten (Table 13-1).

MINERALS

Calcium
Functions

Adequate calcium intake, along with that of vitamin D, is essential for maintenance of bone strength, nerve conduction, muscle contraction, and general inter- and intracellular communication (NRC, 1989).

Intake and Status

Rodahl and Issekutz (1965) reported that Alaskan Eskimos consumed only about one-half to two-thirds the RDA for calcium. Draper (1976) reported a higher than normal rate of bone mineral loss and an increased incidence of osteoporosis among northern Alaskan Eskimos. Mazess and Mather (1976a, b) also observed lower bone mineral content and earlier onset of bone loss among Alaskan and Canadian Eskimos compared to caucasians in the United States. The relatively high consumption of protein, and consequently phosphorus, by these populations may be partially responsible for these findings (NRC, 1989).

Consumption of calcium was increased during Operation Everest II (Rose et al., 1987) but reduced during the women's sojourn to 4,300 m (14,098 ft)

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

(Hannon et al., 1976). Pugh (1965) reported that two climbers who kept a cursory food journal while climbing from 6,400 to 7,600 m (20,984 to 24,918 ft) altitude on Mount Everest consumed 500 and 750 mg of calcium. Rupp et al. (1982) measured a variety of electrolyte changes in blood and urine of members of a Kanchenjunga expedition. They reported a slight, transient (8 percent) decrease in plasma calcium at higher altitudes, which returned to normal within a few days at altitude.

During the 9-wk On Top Everest '89 nutrition research expedition, the 15 members (10 males, 5 females) maintained full dietary records every day, regardless of their camp location. While some of the records were inadvertently lost, there were a total of 842 dietary records collected (out of a possible 945, for an 89 percent completion rate) and analyzed for intake of energy and various nutrients. The calculated intake of calcium was 910 ± 579 mg/d, with no changes or trends occurring as a result of increasing altitudes.

During this expedition, 24-h urine samples were collected at 28 separate times and analyzed for various compounds. Urinary excretion of calcium and of hydroxyproline, both markers for bone demineralization, were within normal ranges, which suggests that there was no loss of calcium. Also, single and dual photon absorptiometry performed immediately prior to departure from the United States, and at approximately 4 weeks following return to the United States, showed no indication of bone demineralization during exposures to these high altitudes.

Author's Recommendation

Because intakes of calcium have been reported to be near that suggested by the RDA and there have been no indications of an inadequate intake or adverse change in status of calcium during the 9-wk period at high and extreme altitude, there is no basis for recommending the micronutrient intake goal of calcium above the current RDA and MRDA levels of 800 to 1,200 mg/d (Table 13-1).

Phosphorus
Functions

Phosphorus is required for bone formation and integrity, with approximately 85 percent of the total phosphorus in the adult body localized in the bones (NRC, 1989). Phosphorus is involved also in energy metabolism in its role as an enzyme modulator and its essentiality for high-energy bonds in ATP and creatine phosphate.

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×
Intake and Status

Consumption of phosphorus generally parallels that of protein (NRC, 1989). Since elevated intakes of phosphorus increase calcium reabsorption (NRC, 1989) by the kidneys, this largely offsets the adverse effect of high protein intake on calcium reabsorption. Rodahl and Issekutz (1965) reported that Alaskan Eskimos consumed about 1.5- to 2-fold greater amounts of phosphorus than that suggested in the RDA (NRC, 1989). This high intake probably resulted from the relatively high protein intake of these people. Increased intakes were also reported during Operation Everest II (Rose et al., 1987) and during the military exercise in Bolivia (Edwards et al., 1991), but Hannon et al. (1976) reported a transient reduction in phosphorus consumption by women during a sojourn to 4,300 m (14,098 ft).

During the 9-wk On Top Everest '89 expedition, there was a reported intake of 1,249 ± 720 mg of phosphorus per day, with no changes in intake occurring as a function of increasing altitudes. Urinary excretion during this expedition was within normal values.

Jain et al. (1987) reported that phosphate supplementation of persons living at low altitudes resulted, by an unknown mechanism, in a more rapid acclimatization to moderate altitudes as evidenced by increased blood levels of 2,3-dephosphoglycerate, a rightward shift in the oxygen-hemoglobin dissociation curve, and improved performance on cognitive function tests.

Author's Recommendation

Because there has been no indication of abnormally low intake or excessive excretion of phosphorus in the cold or at high altitudes, there is no justification for recommending the micronutrient intake goal for phosphorus above the RDA and MRDA level of 800 to 1,200 mg/d (Table 13-1).

Magnesium
Functions

Magnesium is essential for the production of ATP and for numerous other enzymatic reactions. As stated in the RDA (NRC, 1989), "As the complex Mg-ATP2-, magnesium is essential for all biosynthetic processes, glycolysis, formation of cyclic-AMP, energy-dependent membrane transport, and transmission of the genetic code" (p. 188).

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×
Intake and Status

A decreased intake of magnesium was reported by soldiers working in Bolivia (Edwards et al., 1991). Rupp et al. (1982) reported no changes in plasma concentrations of magnesium when climbers were on Kanchenjunga, but daily urinary output of magnesium decreased approximately 50 percent with no comparable decrease in urinary volume. This output returned to normal following a return to lower altitudes and rest. In general, plasma magnesium concentrations are remarkably constant and are not indicative of magnesium status except under conditions of extreme magnesium deficiency (NRC, 1989).

During the 9-wk On Top Everest '89 expedition, magnesium consumption averaged 236 ± 145 mg/d in the 842 daily diet records, with no significant changes or trends in intake related to increasing altitudes possible. Possible magnesium content of snow-melt used for drinking water was not taken into account in determining total intake.

Author's Recommendation

Due to the essentiality of magnesium in energy production, its low toxicity, and the observed low intake during the On Top Everest '89 expedition, the suggested micronutrient intake goal for magnesium is set at 400 mg/d, which is at the upper range set by the MRDA (Table 13-1).

Iron
Functions

Iron is an essential constituent of hemoglobin and myoglobin as well as several enzymes. As much as 30 percent of the body iron is located in storage forms such as ferritin and hemosiderin (NRC, 1989).

Intake and Status

Numerous studies have documented an increase in erythrocytes (polycythemia) during exposure to altitude, wherein hematocrit values reach upwards of 0.65 to 0.70 (Ward et al., 1989a). At these higher hematocrits, the viscosity of blood becomes an issue of concern, especially in the peripheral tissues, which may have become vasoconstricted due to cold exposure. The causes of this polycythemia are beyond the scope of this chapter (for discussion, see Frisancho, 1981). However, due to the essentiality of iron in hemoglobin for

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

the binding and transport of oxygen by erythrocytes, attention must be given to iron status, especially for those working at high altitudes.

Increased consumption of iron occurred during Operation Everest II (Rose et al., 1987) and by soldiers working in Bolivia (Edwards et al., 1991). Worme et al. (1992) reported consumption of an average 30.8 ± 1.06 mg of iron by a group of men and women working at moderate altitudes (2,400 to 4,300 m or 7,875 to 14,110 ft), with a corresponding increase in serum transferrin during the 31-d expedition. There were no changes in transferrin saturation or serum ferritin, with none of the subjects having a serum ferritin concentration of less than 12 g/liter (although plasma volume was not measured). The lack of decline in serum ferritin indicates that there was an adequate intake of iron and of iron stores to prevent onset of iron deficiency brought on by the altitude-induced polycythemia.

Consumption of iron averaged 15.8 ± 12.4 mg/d during the On Top Everest '89 expedition, with a gradual reduction in intake as altitudes increased. Intakes averaged 16.0, 17.1, 15.8, 7.5, and 11.3 mg/d at base camp and at camps 1, 2, 3, and 4, respectively. All members experienced polycythemia for the duration of the expedition.

Reynafarje and Ramos (1961) reported an increase in intestinal iron absorption during the first several days following exposure to 4,500 m (14,754 ft), reaching a maximum after 1 week and gradually declining over the following month. Conversely, iron absorption decreased in natives from high altitudes when they were brought down to sea level, reaching a minimum at 3 weeks and increasing back to their normal high-altitude absorption by 16 months. Following this adaptation to different altitudes, intestinal absorption of iron was similar for natives living in their own localities at either low or high altitudes.

Beard et al. (1990) reported that nonmalnourished women with diagnosed iron-deficiency anemia were more susceptible to exposure to cold water, resulting in a lower rectal temperature, lower plasma thyroxine and triiodothyronine, and a lower rate of oxygen consumption when compared to women who had an equivalent percentage body fat and were at the same stage of their menstrual cycle, but who were not anemic. Beard et al. (1988) also reported that iron-deficient individuals living in La Paz, Bolivia, at altitudes of 3,600 to 4,100 m (11,803 to 13,443 ft) had a lower maximal workload and a lower voluntary maximal oxygen uptake when compared to controls who had an adequate iron status.

Author's Recommendation

With the increasing number of women of child-bearing age being included in expeditions and military maneuvers, special consideration needs to be given to maintaining the adequacy of iron status. Due to the consistently observed

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

increase in hematocrit as a function of exposure to altitude and to the importance of adequate iron in maintaining core body temperature, it is suggested that the micronutrient intake goal iron be set at 15 mg/d for men and at 20 mg/d for women (Table 13-1) (in comparison, the RCW contains 19 mg of iron). These amounts are low enough to prevent the onset of constipation, which is reported by some persons taking higher amounts of supplemental iron. Due to the high suggested dose of vitamin C, which enhances absorption of nonheme iron, the suggested micronutrient intake goal level of iron should be sufficient to prevent onset of an iron deficiency.

Zinc and Copper
Functions

Both zinc and copper are required as enzyme cofactors, with substantial amounts of zinc stored in bone and muscle tissue (NRC, 1989). Trauma and stresses of various types have been shown to increase the rate of urinary zinc excretion (Moser et al., 1985).

Intake and Status

There was an increased consumption of zinc during Operation Everest II (Rose et al., 1987) but a decreased intake during the military exercise in Bolivia (Edwards et al., 1991). Rupp et al. (1982) reported a 2.3-fold increase in plasma zinc and a significant (12-fold) increase in urinary excretion of zinc during exposure to 8,453 m (27,715 ft) on Kanchenjunga. Both levels remained elevated for the duration of the expedition. It has been shown that muscle breakdown will produce elevated plasma and urine zinc concentrations (Moser et al., 1985). Rupp et al. (1982) were apparently not aware of this phenomenon, however, as they were unable to provide a reasonable explanation for the observed changes in plasma and urine zinc.

In an expedition conducted at moderate altitudes (2,400 to 4,300 m [7,869 to 14,098 ft]), Deuster et al. (1992) reported dietary intakes of zinc and copper of 10.6 mg and 1.0 mg/d, respectively, prior to beginning the expedition. These intakes rose to 16.9 mg and 3.5 mg/d, respectively, during the 31-d expedition, and intakes were 15.5 mg and 1.9 mg/d, respectively, following return to sea level. There were no significant changes in concentrations of plasma or urine zinc, or plasma copper at any of these times.

Consumption of zinc during the On Top Everest '89 expedition averaged 8.4 ± 8.7 mg/d, with no variation in intake related to increasing altitudes. Urinary excretion of zinc averaged between 0.5 and 0.9 mg/d, with the maximum excretion being 3.2 mg (Rose et al., 1987). The highest excretion

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

generally occurred during periods of maximum physical exertion, which suggests that the abnormally elevated excretion was the result of muscle tissue breakdown. Neither intake nor status was determined for copper during this expedition.

Author's Recommendation

Because various stresses increase urinary excretion of zinc, the exertion of living and working in the cold or at high altitudes may be sufficient to warrant intake of zinc above the current RDA and MRDA of 15 mg/d. Thus, the suggested micronutrient intake goal for zinc is set at 20 mg/d (Table 13-1). Due to consistently low intakes and periodic high excretions of zinc during the On Top Everest '89 expedition, it is suggested that the micronutrient intake goal of zinc be provided in the foods actually consumed by soldiers or others working in the cold or at high altitudes. This increased amount of zinc is not high enough to adversely affect copper status (NRC, 1989).

There is no indication that recommended intake of copper needs to be set at levels different than the current ESADDI of 1.5 to 3 mg/d. The high micronutrient intake goal for vitamin C (Table 13-1) is probably not high enough to adversely affect copper status.

Other Trace Minerals
Author's Recommendation

There are no known data on the intake of trace minerals by those working in the cold or at high altitude. Until such data exist, there is no basis to recommend intakes of any of the trace minerals at other than RDA or ESADDI levels.

AUTHOR'S CONCLUSIONS AND RECOMMENDATIONS

Although it is generally agreed that a vitamin deficiency will impair physical performance, Williams (1989) stated that "in general, vitamin supplementation to an athlete on a well-balanced diet has not been shown to improve performance" (p. 163). While this may be true for athletes performing at moderate temperatures and at low altitudes, increased intake of several of the micronutrients may be useful to enhance various aspects of health related to survival for those working for prolonged periods in the cold or at high altitudes.

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

Persons who live or who engage in prolonged physical exertion for extended periods of time in the cold or at high altitudes appear to have special nutritional needs. Thus, they are justified in consuming levels of specific vitamins and minerals in amounts greater than that set in either the RDA or the MRDA. The micronutrient intake goals (Table 13-1) are recommended to meet these special needs and should be safe for all the nutrients. Performance may not be enhanced by consumption of vitamins and minerals at the micronutrient intake goal level, but various critical bodily functions may be spared stress and chances of survival may be enhanced under these harsh environmental conditions.

The predominantly Western foods now being consumed by expeditions in the cold and at high altitudes as well as the RCW that is consumed during military operations provide the majority of the essential nutrients in adequate amounts (according to the RDA and MRDA). Supplementation with additional vitamins E, C, and pantothenic acid, however, would ensure that these critical nutrients would be provided in amounts that cannot be obtained from the consumption of food alone. Including other vitamins and minerals at or near the RDA and MRDA levels should ensure adequate nutrient status for all metabolic functions. Amounts of each of the nutrients suggested in the micronutrient intake goal in Table 13-1 are recommended as a prudent and safe guide. The recommended amounts are subject to revision as more data are generated.

As with most areas of scientific investigation, substantially more research is needed to establish the effects of cold and altitude on vitamin and mineral requirements. Due to the critical role of vitamins and minerals in energy production, a well-designed human study should be conducted in a location such as the South Pole or Fort Greely, Alaska. During such a study, intake, excretion, and numerous status indices for each of the vitamins and minerals can be measured accurately and correlated with energy intake, expenditure, changes in body composition, and environmental conditions. Duration of this study must be sufficient to allow for changes in nutrient status if any, to occur; that is, a range of 3 to 4 months.

Whereas simulated high altitudes, such as those produced by the excellent studies conducted during Operation Everest II, can be used to investigate the effects of low oxygen pressure on nutrient intakes and changes in status, such hypobaric chamber experiments cannot duplicate the massive expenditures of energy, the prolonged exposure to cold, and the psychological concerns regarding danger and isolation that occur during actual expeditions to high altitudes. For this reason, hypobaric chamber experiments should be viewed as providing supplemental rather than primary information on the effects of high altitudes on vitamin and mineral requirements. There is still a need for well-designed experiments to be conducted at high altitudes to provide the data necessary to determine vitamin and mineral requirements. Even though such research expeditions are logistic nightmares compared to strict mountain

Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
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climbing expeditions, research expeditions such as the American Medical Research Expedition on Everest (West, 1984) and On Top Everest '89 demonstrate unequivocally that they can be done.

Good nutritional status is mandatory for those facing prolonged periods in the cold or at high altitudes. Survival in such environments depends, in large part, on adequate mental, physical, and nutritional preparation prior to and during exposures to extreme cold or high altitude.

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Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
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Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

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Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
×

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Suggested Citation:"13 Effects of Cold and altitude on Vitamin and Mineral Requirements." Institute of Medicine. 1996. Nutritional Needs in Cold and High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press. doi: 10.17226/5197.
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This book reviews the research pertaining to nutrient requirements for working in cold or in high-altitude environments and states recommendations regarding the application of this information to military operational rations. It addresses whether, aside from increased energy demands, cold or high-altitude environments elicit an increased demand or requirement for specific nutrients, and whether performance in cold or high-altitude environments can be enhanced by the provision of increased amounts of specific nutrients.

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