Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride (1997) / Chapter Skim
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7 Vitamin D
7 Vitamin D
Pages 250-287
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From page 250... ...
. Vitamin D's major biologic function in humans is to maintain serum calcium and phosphorus concentrations within the normal range by enhancing the efficiency of the small intestine to absorb these minerals from the diet (DeLuca, 1988; Reichel et al., 1989)
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VITAMIN D Acetate 24 11/,,' · . HO\`,, - ~ A7~se ,,,t: Cholesterol HO" 7-Dehydrocholestero' UVB,l~ ,...
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From page 252... ...
promotes the synthesis of 1,25 (0H) 2D3, which, in turn, stimulates intestinal calcium transport and bone calcium mobilization, and regulates the synthesis of PTH by negative feedback.
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From page 253... ...
2D in the brain, heart, pancreas, mononuclear cells, activated lymphocytes, and skin remains unknown, its major biologic function has been iclentifieci as a potent antiproliferative and proclifferentiation hormone (Abe et al., 1981; Colston et al., 1981; Eisman et al., 1981; Smith et al., 1987)
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From page 254... ...
D results in approximately two to five times more activity than giving vitamin D itself in curing rickets and in inducing intestinal calcium absorption and mobilization of calcium from bones in rats. However, at physiologic concentrations, it is biologically inert in affecting these functions (DeLuca, 1984~.
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From page 255... ...
In adults over age 65 years, there is a fourfold decrease in the capacity to produce vitamin D3 when compared with younger adults aged 20 to 30 years (Holick et al., 1989; Neeci et al., 1993~. Although one study suggested that there may be a defect in intestinal calcium absorption of tracer quantities of vitamin D3 in the elderly (Barragry et al., 1978)
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From page 256... ...
An increase in skin melanin pigmentation or the topical application of a sunscreen will absorb solar ultraviolet B photons and thereby significantly recluce the production of vitamin D3 in the skin (Clemens et al., 1982; Matsuoka et al., 1987~. Latitude, time of clay, and season of the year have a dramatic influence on the cutaneous production of vitamin D3.
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From page 257... ...
. All proprietary infant formulas must also contain vitamin D in the amount of 10 fig (400 IU)
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From page 258... ...
PTH stimulates the mobilization of calcium from the skeleton, conserves renal loss of calcium, and causes increased renal excretion of phosphorus leaciing to a normal fasting serum calcium with a low or low-normal serum phosphorus (Holick, 1995~. Thus, vitamin D deficiency is characterized biochemically by either a normal or low-normal serum calcium with a low-normal or low-fasting serum phosphorus and an elevated serum PTH.
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From page 259... ...
Two pathologic indicators, racliologic evidence of rickets (Demay, 1995) and biochemical abnormalities associated with metabolic bone disease, inclucling elevations in alkaline phosphatase and PTH concentrations in the circulation (Demay, 1995)
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From page 260... ...
The few studies conclucteci in African Americans and Mexican Americans suggest that these population groups have lower circulating concentrations of 25~0H) D and higher serum concentrations of PTH and 1,25~0H)
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From page 261... ...
Furthermore, the amount of vitamin D found naturally in foocis, such as fish liver oils, fatty fish, and egg yolks, is very clepenclent on the time of the year these foods are harvested. Studies that report the clietary intake of vitamin D baseci on the expected amount of vitamin D fortification of milk, margarine, cereals, and breacis are highly suspect because the analysis of the vitamin D con
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From page 262... ...
Infants age ci O to 6 months who are born in the late fall in far northern and southern latitudes can only obtain vitamin D from their own stores, which have resulted from transplacental transfer in utero, or from that provicleci by the cliet, including mother's breast milk, infant formula, or supplements. Because human milk has very little vitamin D, breast-feci infants who are not exposed to sunlight are unlikely to obtain adequate amounts of vitamin D from mother's milk to satisfy their needs beyond early infancy (Nakao, 1988; Specker et al., 1985b)
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From page 263... ...
D concentrations, clue to the overwhelming effect of sunlight exposure on the infant's vitamin D status (Ala-Houhala, 1985; Ala-Houhala et al., 1986; Feliciano et al., 1994; Hillman, 1990; Markestaci and Elzouki, 1991~. Serum 25~0HJD, Linear Growth, and Bone Mass.
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From page 264... ...
D concentrations in human milk-fed infants not receiving vitamin D supplements decreased in winter due to less sunlight exposure. However, this decrease did not occur in infants receiving a vitamin D supplement of 10 fig (400 IU)
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From page 265... ...
They found that an average intake of vitamin D as low as 4 fig (160 IU) /ciay in the experimental formula maintained normal and stable vitamin D status, physical growth, biochemical and hormonal inclices of bone mineral metabolism, and skeletal radiographs.
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From page 266... ...
/day of vitamin D maintained 25~0H) D levels in the normal range, but below circulating concentrations attained by infants in the summer.
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From page 267... ...
In a longitudinal study in Norway, where sun exposure is presumed to vary over the year, an intake of vitamin D of about 2.5 fig (100 IU) /ciay from fortified margarine maintained normal vitamin D status in children age ci 8 to 18 years (Aksnes and Aarskog, 1982~.
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From page 268... ...
The increaseci blood concentrations of 1,25~0H) 2D enhance intestinal calcium absorption to provide adequate calcium for the rapidly growing skeleton.
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From page 269... ...
There is little scientific information that relates vitamin D intake, bone health, and vitamin D status as cletermineci by serum 25~0H) D and PTH concentrations in young adult and adult age groups.
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From page 270... ...
Taken together, these studies suggest that adults younger than 50 years of age in the United States depend on sunlight for most of their vitamin D requirement. Physiological reliance on dietary vitamin D probably only occurs in the winter months in a small proportion who are not exposed to sunlight during the summer.
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From page 271... ...
. Serum PTH concentrations were significantly higher in the vegetarians (57 ng/liter)
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From page 272... ...
, serum PTH concentrations were elevated in winter (between March and May) in women consuming less than 5.5 fig (220 IU)
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From page 273... ...
There is strong evidence for a decrease in circulating concentrations of 25~0H) D and increased risk of skeletal fractures with aging, and it is most apparent after the age of 70 years (Chevalley et al., 1994; Dawson-Hughes et al., 1991; Horclon and Peacock, 1987; Lamberg-Allarcit et al., 1989; Lips et al., 1988; McGrath et al., 1993; Ng et al., 1994; Ooms et al., 1995; Villareal et al., 1991; Webb et al., 1990)
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From page 274... ...
. for vitamin D deficiency, which causes secondary hyperparathyroidism and osteomalacia and exacerbates osteoporosis, resulting in increased risk of skeletal fractures (Chapuy et al., 1992; Egsmose et al., 1987; Honkanen et al., 1990; McKenna, 1992; Pietschmann et al., 1990~.
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From page 275... ...
One of the mechanisms by which glucocorticoicis induce osteopenia is by inhibiting vitamin D-clepenclent intestinal calcium absorption (Lukert and Raisz, 1990~. Therefore, patients on glucocorticoici therapy may require aciclitional vitamin D in order to maintain their serum 25~0H)
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From page 276... ...
/ciay of vitamin D It was conclucleci that vitamin D supplementation increased circulating concentrations of 25~0H)
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From page 277... ...
D concentration in the normal range cluring lactation, and there is no evidence that lactation increases a mother's AI for vitamin D Therefore, it is reasonable to extrapolate from observations in nonlactating women that when sunlight exposure is inadequate, an AI of 5.0 fig (200 IU)
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From page 278... ...
Resorption of bone (hyperosteolysis) has been shown to be a major contributor to the hypercalcemia associated with hypervitaminosis D in studies that demonstrated rapid decreases in blood calcium levels following the
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From page 280... ...
The plasma (or serum) calcium levels reported range from 2.82 to 4.00 mmol/liter (normal levels are 2.15 to 2.62 mmol/liter)
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From page 281... ...
(1984) stuclieci serum calcium levels in humans, with and without tuberculosis, where cliet was supplemented with tinily vitamin D doses of 10, 20, 30, 60, and 95 fig (400, 800, 1,200, 2,400, and 3,800 IU)
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From page 282... ...
. For example, the mean serum calcium level in normal controls following administration of 60 fig (2,400 IU)
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From page 283... ...
found retarcleci linear growth in 35 infants up to 1 year of age who received 45 to 112.5 fig ~ 1,800 to 4,500 IU) /day of vitamin D as supplements (without regard to sunlight exposure, which was potentially considerable cluring the summer months)
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From page 284... ...
This is because of the inaccuracies of survey ciata, but also and more importantly, because sunlight exposure was not reported, and the level of fortification of fooci was probably not accurately cletermineci, and was most likely unclerest~mateci. Uncertainty and Uncertainty Factors.
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From page 285... ...
/day Pregnancy and Lactation The available ciata were jucigeci inadequate to derive a UL for pregnant and lactating women that is different from other adults. Given the minor impact on either circulating vitamin D levels or serum calcium levels in utero or in infants seen with vitamin D supplements of 25 and 50 fig (1,000 and 2,000 IU)
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From page 286... ...
D to 1,25~0H) 2D and the efficiency of intestinal calcium absorption, thereby satisfying the increased calcium requirement by the rapidly growing skeleton.
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From page 287... ...
Therefore, more studies are neecleci to evaluate other parameters of calcium metabolism as they relate to vitamin D status including circulating concentrations of PTH. · The development of methodologies to assess changes in body stores of vitamin D is neecleci to accurately assess requirements in the absence of exposure to sunlight.
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