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Nutritional Status of the U. S. Population: Iron, Vitamin C, and Zinc CATHERINE WOTEKI, CLIFFORD JOHNSON, Ad ROBERT MURPHY Conclusions can be drawn about the nutritional status of Americans by relating data on selected indicators of nutritional status to data on food consumption from two federal surveys: the second National Health and Nutrition Examination Survey (NHANES II), conducted by the Depart- ment of Health and Human Services (DHHS), and the Nationwide Food Consumption Survey (NFCS), conducted by the U.S. Department of Ag- riculture (USDA). In the first paper of this session, Dr. Welsh reviewed the sufficiency of nutrition-related data from the two most recent of these surveys. For some nutrients, a substantial quantity of data is available from both surveys. For other nutrients, data on dietary intake, on nutri- tional status, or on both may be of limited quantity or quality for a variety of reasons. To illustrate how conclusions about the nutritional status of Americans can be drawn from these surveys, three nutrients are discussed: · iron, for which sufficient data are available to assess both nutritional status and dietary intake; · vitamin C, for which there is only one indicator of nutritional status but sufficient dietary intake data; and · zinc, for which there is one indicator of nutritional status and no data on dietary intake. DATA SOURCES The NHANES II was conducted by the DHHS National Center for Health Statistics from 1976 through 1980 on a national probability sample 21
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22 EATING PA77ERNS, NUTRlTlON, AND BEALTH of Americans aged 6 months through 74 years who were representative of the civilian, noninstitutionalized population (McDowell et al., 19811. The results of this survey provide an opportunity to assess the U.S. pop- ulation's health and nutritional status and, by comparing the data with results of earlier surveys, to learn how this status has changed over time. The NHANES lI sample consisted of 27,801 persons from 64 geographical locations in the United States. Of these, 20,322 (73~o) were interviewed and given a standardized physical examination. A detailed description of the survey design and its operations has been published in the Vital and Health Statistics Series of He National Center for Heals Statistics (McDowell etal., 19811. The NFCS was conducted by the USDA Human Nutrition Information Service during 1977 and 1978 on a national probability sample of Amer- ican households that were representative of the 48 coterminous states. It provides information on household food use over 7 days and household members' food and nutrient intakes over 3 days. The NECS sample con- sisted of approximately 15,000 households and 36,Q00 persons residing in these households. Detailed descriptions of the household and individual surveys have been published (USDA, 1982, 19831. IRON Data from PLANES 11 A primary focus of NHANES II was the characterization of the prev- alence and possible cause of anemia in the U.S. population. To make this characterization, the survey team collected and analyzed blood specimens and reported values for hemoglobin, hematocrit, complete blood count, mean corpuscular volume, transfe~in saturation, erythrocyte protopor- phyrin, serum ferritin, serum vitamin By, serum folate, and erythrocyte folate. In 1983, at the request of the Food and Drug Administration, the Fed- eration of American Societies for Experimental Biology (FASEB) con- vened an expert Scientific Working Group (ESWG) to evaluate the appropriateness of the NHANES lI measures and methods used, recom- mend interpretative criteria, estimate the prevalence of impaired iron sta- tus, and identify groups at greatest risk. Its report (FASEB, 1984a) is the source of the following discussion. The ESWG developed two models based on four variables: serum fer- ritin, erythrocyte protoporphyrin, transferrin saturation, and mean cor- puscular volume (MCV). The ferritin model is used to estimate early stages of iron store depletion and is based on measures of serum ferritin, .
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NUTRITIONAL STATUS OF THE U.S. POPULATION 23 TABLE 1 Criteria Defining Abnormal Values of Four Measures of Iron Nutriture for Five Age Groupsa - Serum Transferrin E~ythrocyte Age Femtin Saturation Protoporphynn MCV (year) (ng/ml) (%) (,ug/dl RBCb) (fl) 1-2 NMC 80 <73 3-4 75 <75 5-10 70 <76 11-14 70 <78 15-74 70 <80 aData from FASEB, 1984a. bRBC, red blood cell. CNM, not measured. erythrocyte protoporphyr~n, and ~ansfernn saturation. The later stages of iron depletion are estimated with the MCV model, which is based on measures of mean corpuscular volume, ery~rocyte protoporphynn, and transfernn saturation. The criteria defining abnormal values for each var- iable are shown in Table 1. To be categorized as having impaired iron status, a person had to have at least two of three values in the abnormal range. The prevalence estimates derived from the two models are shown in Figures 1, 2, and 3. Children aged 1 Trough 2 years had the highest 20 - . 10 o 1 -2 I Confidence interval Ferritin model MCV Model - 9.4 3.9 _ 3-4 5-10 Age (Years) FIGURE 1 Prevalence of impaired iron status for American children aged 1 through 10 years, by model. Data from the second National Health and Nutrition Examination Survey (FASEB, 1984a).
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24 EATING PATTERNS, NUTRITION, AND lIEALTl1 20 10 o I Confidence interval O Ferritin model MCV model B1_~ 11-14 15-19 20-44 45-64 Auto (Years) 65-74 FIGURE 2 Prevalence of impaled iron status for American males aged 11 through 74 years, by model. Data from the second National Health and Nutrition Examination survey (FASEB, 1984a). 20 4- e, cad 10 o 9.6 3.4 . I Confidence interval LJ Ferritin model ~ MCV model lt-14 15-19 20-44 45-64 65 74 Age IYearsJ FIGURE 3 Prevalence of impaired iron status for American females aged 11 through 74 years, by model. Data from the second National Health and Nutrition Examination Survey (FASEB, 1984a).
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NUTRITIONAL STATUS OF THE U.S. POPULATION 25 prevalence of impaired iron status (9%) by the MCV model. Because serum ferritin was not measured in children in that age group, prevalence estimates using Me fe~ritin model cannot be presented for those children. As expected, the ferritin model produced slightly higher prevalence es- timates than did the MCV model for all sex and age groups. The groups with the highest prevalences were children aged 1 through 2 years, males aged 11 through 14 years, and females aged 15 through 44 years. Data from NFCS Dietary data from the NFCS (Welsh, 1984) indicate that the groups with the highest prevalences of impaired iron status had the lowest intakes of Me Recommended Dietary Allowances (RDA) for iron (NRC, 19801. Children aged 1 through ~ years, males aged 9 through 18 years, and females aged 9 through 64 years had mean intakes below the RDA (Figure 4~. About 37% of children aged 1 through ~ years and males aged 9 through 18 years of age consumed diets providing at least 100% of the RDA for iron over 3 days. The comparable figure for females aged 9 Trough 64 years was less Man 20%. These data indicate that the highest prevalence of impaired iron status =~ ~ a\) ~ ~ Males Females 74 l ! ~3 ~8 1 < 1 1-8 9-18 Age (Years) 19-64 >65 FIGURE 4 Individual intakes of iron: mean percentages of 1980 Recommended Dietary Allowances (RDAs), by sex and age (3-day average). Adapted from Welsh, 1984.
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26 EATING PATTERNS, NUTRITION, AND HEALTH in the United States occurs in those groups with the lowest dietary intake of iron, expressed as a percentage of He RDA. However, the magnitude of the numbers is quite different. Although a substantial proportion of the U.S. population does not report diets containing the full RDA for iron, the overall prevalence of impaired iron status is low. VITAMIN C Assessments of vitamin C have been included in national surveys to determine the prevalence of scurvy and the proportion of the population at risk of deficiency. In recent years, interest in the vitamin C status of Americans has increased as evidence has accumulated for the role of the vitamin in inhibiting the formation of some carcinogens and for the as- sociation of the consumption of vitamin C-conta~ning foods with a lower risk of stomach and esophageal cancer. Data from NHANES 11 By using data from NHANES it, one can identify and characterize subgroups of the population with low serum vitamin C. Diet, smoking habits, and other lifestyle factors that affect serum vitamin C levels can be examined. As part of He nutritional biochemist assessments, serum vitamin C was to be analyzed for all persons aged 3 Trough 74 years as an indicator of vitamin C status. Of the 18,549 persons aged 3 Trough 74 years in the sample, however, the serum vitamin C values were recorded for only 15,796 (85%~. The determinations were performed at ttie Centers for Disease Control using a modified calorimetric ascorbic acid method (Gunter et al., 1985~. Mean serum vitamin C levels differed by age and sex (Figure 51. For children, mean levels generadly decreased with age from a high of about 1.5 mg/dl for He 3- through 5-year-old group to 1.1 mg/~! for He 15- through 17-year-old group. For adults, mean values remained fairly stable, although there was some increase in values for the older age group. Males had lower mean levels of serum vitamin C than did females for all the adult age categories. The findings are reflected in the prevalence of low serum vitamin C levels in the surveyed population (Figure 6), where low was defined as less than 0.25 mg/dl. Very few children had low serum vitamin C levels. The prevalence of low values generally increased for teenagers, and adult males had a higher proportion of low values (5.6%) than did females (2.7%~.
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NUTRITIONAL STATUS OF THE U.S. POPULATION 1.61 1.4 Cry `,' 0.8 0.6 \ \ \ \ \ 27 Female - Male 1 1 1 1 1 1 1 1 0 10 20 30 40 50 60 70 Age (Years) FIGURE 5 Mean serum vitamin C levels of Americans, by age and sex, 1976-1980. Unpublished data from the second National Health and Nutrition Examination Survey. 10 8t 61 4 - 0 C' con 4 2f o l ~ 0.1 0; T 0.1 ~0.0 ~/ M F M ~ 3 5 years 6-11 years 1 loll F l ~ M F M F 12-19 years Age and Sex Groups 20-44 years 45-74 years FIGURE 6 Percentage of Americans with low serum vitamin C levels, by age and sex, 1976-1980. Low serum vitamin C is defined as less than 0.25 mg/dl. Unpublished data from the second National Health and Nutrition Examination Survey. -
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28 EATING PATTERNS, NUTRITION, AND HEALTH Following is a list of the major variables generally believed to be associated with serum vitamin C status: age, sex, race poverty status ~ vitamin-mineral supplement use (regular users as opposed to irregular or nonusers) ~ cigarette smoking (current cigarette smokers; not pipe smokers, cigar smokers, or nonsmokers) · oral contraceptive use · dietary intake of vitamin C · frequency of consuming foods rich in vitamin C · fasting or nonfasting examination status · morning or afternoon examination · pregnancy status Many of these characteristics were found to be significantly related to serum vitamin C. Because of the relatively high percentage of low serum vitamin C levels in adults and because of differences between males and females, we characterized the population aged 20 through 74 years by cigarette-smok- ing status, dietary supplement use, and poverty Status. Preliminary analysis of our data (Johnson et al., 1984) had shown these factors to be associated with serum vitamin C levels. The percentage of adults aged 20 through 44 years and 45 through 74 years in each of the cigarette-smoking and supplement use categories in the population are presented in Figure 7. The proportion of current cigarette smokers was higher in the younger adults. However, regular supplement use was highest in the 45- through 74-year-old age group. The percentage of the population in each of the cate~ones was sufficient for more detailed analysis of the data. Mean serum vitamin C levels were significantly higher for regular supplement users (1.3-1.5 mg/dl) than for irregular or nonusers (0.7-1.1 mg/dl) for both males and females in each cigarette-smoking category (Figure 8~. With one exception, persons in the other smokers/nonsmokers group had higher mean serum vitamin C levels than did current cigarette smokers for each sex and supplement-use category. These differences in smoking and supplement use categories for virgin C status were even more pronounced when Me prevalence of low serum vitamin C values (Figure 9) was considered. Males who used supplements regularly had prevalences less Man 1%, regardless of Weir cigarette-smoking status. Irregular or nonusers of supplements had higher levels; 45- through
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NUTR~ION~ STATUS OF THE U.S. POPULATION 70 _ 60 50 40 30 20 10 41 ~ Regular 59 ~ supplement user chinarregularlnonuser of /~ supplements 31 Current cigarette smokers Ages 20~44 Other smokers! nonsmokers 29 69 ,. Current Other cigarette smokers! smokers nonsmokers Ages 45~64 FIGURE 7 Current cigarette-smoking status and dietary supplement usage of Amer- icans, by age group, measured as a percentage of the population, 1976-1980. Un- published data from the second National Health and Nutrition Examination Survey. 2.0 - - ~ 1.0 ._ E In o.o T T - _ . , . M F __ . M F Regular Incubi or supplement user nonuser Current c~garene smokers - ; ~ . lo: _ ~ lo_ 191 F Regular supplement user 1 M f Irregular or or nonuser Other smokersinonsmokers FIGURE 8 Mean serum vitamin C levels of Americans aged 21 through 74 ~rears, by sex (pregnant women excluded), current cigarette-smoking status, and dietary supplement usage, 197~1980. Unpublished data from the second National Health and Nutrition Examination Survey.
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30 20 15 10 5 EATING PATTERNS, NUTRITION, AND HEALTH [~3 Regular supplement 5: ~ user . . ~ ·, Irregular or nonuser of supplements 00 ~ 0\ 09?~ ~ Current cigarette Other smokers! Current cigarette Other smokers/ smokers nonsmokers smokers nonsmokers Ages 20-44 Ages 45-74 FIGURE 9 Percentage of-American males aged 20 through 74 years with low serum vitamin C levels, by age group, current cigarette-smoking status, and dietary supple- ment usage, 1976-1980. Low serum vitamin C is defined as less than 0.25 mg/dl. Unpublished data from the second National Health and Nutrition Examination Survey. 20 0 `,, 10 5 o ~ _ _ — o.s- _ ~ _ ~ ;~ ... Regular supplement ....... user ~ Irregular or nonuser of .. ~ supplements 1~ 2~ Current cigarette Other smokers! smokers nonsmokers Ages 20-44 Current cigarette Other smokers/ smokers nonsmokers Ages 45-74 FIGURE 10 Percentage of American females (pregnant women excluded) aged 20 through 74 years with low serum vitamin C levels, by age group, current cigarette- smoking status. and dietary supplement usage, 1976-1980. Low serum vitamin C is defined as less than 0.25 mg/dl. Unpublished data from the second National Health and Nutrition Examination Survey.
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NUTRITIONAL STATUS OF THE U.S. POPULATION 31 74-year-old males who were current cigarette smokers had the highest prev- alence (16.4%), followed by 20- through 44-year-old males (9%~. With one exception, we observed the same pattern for females as for males (Figure 10~. The percentage of women with low serum vitamin C was low for all subpopulations that used supplements regularly. Only current cigarette smolders who did not use supplements regularly had a prevalence greater than 5%. Because serum vitamin C reflects dietary intake, we used this measure to determine the vitamin C content of the diets of males and females classified by cigarette smoking and supplement use. Figure 11 shows Cat for median vitamin C intake based on a single 24-hour recall among males, regular supplement users had higher dietary levels~than did Regular or nonusers within each age and smoking status category. Intakes by current cigarette smokers were lower than Rose for the other smoker/nonsmoker groups for all age and supplement use categories. Two groups had median vitamin C intakes below We 1980 RDA of 60 ma: We current cigarette smokers who were uregular or nonusers of supplements in bow age groups. Figure 12 shows a pattern for females similar to that observed in males. Within cigareKe-smoking groups, the females aged 45 through 74 years had higher median intakes than did the younger adult women. The younger cigarette smokers and other smokers/nonsmokers not taking supplements had median intakes below the RDA of 60 ma. The vitamin C density of the diets of male supplement users was higher than the median intakes of irregular or nonusers of supplements (Figure 131. We observed a similar pattern for females (Figure 141. We also compared the frequency with which fruits and vegetables high in vitamin C were consumed and found patterns similar to the median intake and intake per 1,000 kcal (Figures 13 and 141. Although the overall percentage of 3- through 74-year-old persons with low serum vitamin C levels was not large (about 3%), this was not true for selected populations. There was a much higher percentage of low serum vitamin C values among cigarette-smoking adults who seldom or never used vitamin-mineral supplements than would be expected by their representation in the population. For males, 34% were current cigarette smokers who did not regularly use vitamin-mineral supplements. In this group, 71 No of the men had low serum vitamin C. The comparable figures for women were 25% and 61~o. In contrast, regular supplement users constituted approximately 20% of the male population, but less than 2% of the low serum vitamin C group. For women, regular supplement users constituted about 28% of the population and less than 8% of the low serum vitamin C group. Because a smaller proportion of the low-income population reported regular
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32 110 100 - CJ) 9o E - 0 80 _ ~ 70 _ ._ (,) 60 _ ._ ~ 50 _ :. 40 _ , ~ 10 _ EATING PATTERNS, NUTRITION AND HEALTH 110 _ ~ supplement user i: ::: :~: Irregular or .: - ~ nonuser of :::::. supplements . . . c::::: ~ ~ ~.~3j~' o ~. ~n ~. ~. Current cigarette Other smokers! smokers nonsmokers Ages 2044 53 it' Current cigarette Other smokers/ smokers nonsmokers Ages 45-74 FIGURE 1 ] Median vitamin C intake of American males aged 20 through 74 years, by age group, current cigarette-smoking status, and dietary supplement usage, 1976- 1980. Unpublished data from the second National Health and Nutrition Examination Survey, 110 100 - ~ 90 - ~ 80 ye C 70 ._ Cal 60 ._ I: 50 40 44 £= ~ To- Current cigarette smokers Ages 20-44 -r ;;.;~ Regular t: A: ~ supplement user ~ ~ Irregular or nonuser of supplements 86 ...... ::::: :~:-:~:~:~- ,.~:,:, ~:i? , Other smokers! Current cigarette Other smokers/ nonsmokers smokers nonsmokers 86 :::~::. a::-::-:-: .2.: :.:. ::~: ::e ....... · .::::. :~:~:~:~:~: :::::: A::::: ~ l 106 __ ...... ;~:-:~:~:~:- :~:~:~:~:~: ·:~:~:~:~:. ...... a::::: :::.:: .......... 78 :-:-::-:: _ ·~ _ ...... _ ·:~:-:-:-:. _ :::::: ~ a::::: _ :::::: _ :::-::: _ ::::: _ :~:~:~:~:~: _ a::::: ::::: . -.- _ Ages 45-74 FIGURE 12 Mean vitamin C intake of American females (pregnant women excluded) aged 20 through 74 years, by age group, current cigarette-smoking status, and dietary supplement usage, 1976-1980. Unpublished data from the second National Health and Nutrition Examination Survey,
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NUTRITIONAL STATUS OF THE U.S. POPULATION 80 = y lo ~7 E - y 40 ._ ~ 20 ._ · - o _ 29 1 2 _s Current cigarette 31 smoicers nonsmokers Ages 20-44 67/A Regular supplement user 43 Other smokers! Current cigarette Other smokers/ - smokers nonsmokers Ages 45~74 Irregular or nonuser of supplements ~2 25 50 is/// A//. is// 40 33 FIGURE 13 Median vitamin C intake per 1,000 kcal of American males aged 20 through 74 years, by age group, current cigarette-smoking status, and dietary sup- plement usage, 1976-1980. Unpublished data from the second National Health and Nutrition Examination Survey. 80 y lo o 60 lo - E 0 40 y ._ ~ 20 ._ ._ o - 27 Regular supplement 25 Irregular or nonuser of supplements ~5 39 60 __ 41 , ~ ~ _ _ ~ ~ _ Other smokers/ Current cigarette smokers 77 _ ~ Other smokers/ nonsmokers 61 Current cigarette smokers nonsmokers Ages 20-44 Ages 45-74 FIGURE 14 Median vitamin C intake per 1,QOO kcal of American females aged 20 through 74 years (pregnant women excluded), by age group, current cigareue-smoking status, and dietary supplement usage, 1976-1980. Unpublished data from the second National Health and Nutrition Examination Survey.
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34 EATING PA7TERNS, NUTRITION, AND HEALTH use of vitamin-mineral supplements than did the general population, we determined the prevalence of low serum vitamin C by poverty status and supplement usage (Figure 151. The percentage of regular supplement users win low serum vitamin C levels was 1% or less, regardless of age, sex, or income. However, among irregular or nonsupplement users, those below poverty had higher prevalences of low serum vitamin C. Males aged 45 Trough 74 years had He highest prevalence of low values (24.2%~. A low serum vitamin C level indicates a low or inadequate intake of vitamin C, probably with low tissue reserves present. On He basis of this indicator, we have identified the following subpopulations win lifestyles that place Rem at high risk for poor vitamin C nutritional status: · consumers of diets Hat are low in vitamin C because of infrequent consumption of vitamin C-rich foods and low vitamin C density of these diets, · cigarette smokers, · irregular or noncons~uners of vitamin or mineral supplements, and · He poor. 0 5 _ C' ct n no Regular supplement user 1.0 0.9 Male Female 20-44 years Male Female 45-74 years Irregular or nonuser of supplements 24.2 25 , _ 20 _ - , ~ PIR < 1 I,, 15 - V77~ PIR >1 ¢, 10 7.1 5 _ ~ 5.0 ~ 3.2 20-44 years 7.9 7.8 45-74 years FIGURE 15 Prevalence of low serum vitamin C in the United States, by age, dietary supplement usage, and poverty income ratio (PIR), 1976-1980. Unpublished data from the second National Health and Nutrition Examination Survey.
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NUTRITIONAL STATUS OF THE U.S. POPULATION Data from NFCS 35 Data on vitamin C from the NFCS indicate Rat mean intakes over 3 days exceeded Me RDA for all sex and age groups (Table 2) and that mean intakes for men were higher than Rose for women aged 9 Trough 64 years. Those win a poverty income ratio (PIR) of 1 or more had higher mean intakes Can those win a PIR of less Can 1. TABLE 2 Individual Intakes of Vitamin C, Measured as Mean Percentage of 1980 RDAs, by Selected Characteristics (3-Day Average), 1977-1978a , Percentage of RDA Category All persons: Males and females: 1 year 1-8 years Males 9-18 years 19-64 years —65 years Females: 9-18 years 19-64 years 265 years Poverty status and race: Above poverty, white Above poverty, black Below poverty, white Below poverty, black Region: Northeast North central South West Urbanization: Central city Suburban Nonmetropolitan Season: Spring Sununer Fall Winter 147 226 166 174 145 153 152 128 150 149 152 125 138 160 147 131 159 152 153 136 151 152 140 146 aUnpublished data from the Nationwide Food Consumption Survey.
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36 EATING PANE - S. NUTRITION, ED HE^TH Lifestyle variables, such as smoking habits and use of supplements, influence serum vitamin C, which is one measure of nutritional status. National dietary surveys have not provided the necessary information for survey analysts to calculate He nutrient contribution of supplements to daily intakes, and this information may not be available in the future because of the difficulty of maintaining a vit~nin-mineral supplement composition data bank. Because 40% of the adult population is presently taking supplements (Gallup Organization, Inc., 1982), dietary intake alone is an inadequate predictor of serum vitamin C. What remains to be de- terrnined is whether a better measure of long-term vitamin C status will be developed and how it will relate to dietary survey results. ZINC Data from NHANES II In NHANES Il. serum zinc was measured by flame atomic absorption spectroscopy of serum samples obtained from 14,770 persons aged 3 through 74 years. Although at the time of the survey serum zinc was recognized as an inadequate measure for the definitive assessment of zinc nutritional status, the Centers for Disease Control wanted to test whether conditions could be maintained for trace element determinations in a large field survey. The ESWG, in which evaluations of iron nutriture were based on data from NHANES II, also made observations on zinc nutriture (FASEB, 1984b). Because serum zinc values differ, depending on the time of blood collection and fasting, the ESWG recommended that different cutoff points be used to define low values for samples obtained in the morning for fasting and nonfasting persons and for afternoon aIld evening samples. These values are shown ire Table 3. ~ A TABI-E 3 Cutoff Points Used to Define Low Serum Zinc Values for Samples Obtained at Different Times of Day and Fasting Conditionsa Serum Zinc Time of Day Fasting Status (,ug/dl) Morning Fasting 70 Morning Nonfasting 65 Afternoon and Presumed fasting 60 evening . . . . _ Data from FASEB, 1984b.
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NUTRITIONAL STATUS OF THE U.S. POPULATION 10 8 6 0 Q 4 2 rid 37 [ ~ Male Female T d~ Al lore I ~ 1 :-:: ::::: :::::::::: . ..~, . _ ~ v 3-8 9-19 20-44 45-64 65-74 Age (years) FIGURE 16 Percentage of Americans with 1QW serum zinc levels, by sex and age. Data from the second National Health and Nutrition Examination Survey (FASEB, 1984). Figure 16 shows that the prevalence of 1DW serum zinc values in the NHANES II sample ranged from 1% in males to 4% in females. The prevalence of low values was slightly higher in young children and the elderly than in adolescents and young adults. These observations provide some indication of groups that should be evaluated in greater depth; how- ever, serum zinc levels are only suggestive of poor zinc nutriture for reasons discussed below. Data on Dietary Intake No conclusions can be drawn about the adequacy of zinc levels in the American diet because neither NHANES II nor NFCS estimated zinc intakes. At the time those surveys were conducted, the data on He zinc content of foods were not complete enough to make reliable estimates. The only national-level data on zinc are the per capita availability of zinc in the food supply (Welsh and Marston, 1983~. Between 1909 and 1981, the zinc level of the food supply fluctuated between 11 and 13 mg per capita per day—a level considerably below the RDA of 15 mg for adults or the RDA of 14.2 mg for the population, which was derived by taking into account the distribution of sex-age groups within the United States in 1981.
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38 EATING PATTERNS, NUTRITION, AND HEALTH Until better methods for measuring nutritional status and more extensive food composition data are available, national surveys will be unable to assess zinc nutritional status. CONCLUSIONS For such nutrients as iron, vitamin C, and zinc there are various kinds of survey data, and conclusions about dietary sufficiency can be made with differing levels of confidence. Dietary surveys (e.g., NFCS) indicate groups with low intakes; however, because most persons' nutrient re- quirements are less than the full RDA, these groups may not, in fact, be malnourished. Thus, dietary surveys only suggest groups at risk for poor nutritional status. In nutritional status surveys (e.g., NHANES II) bio- chemical tests are used to determine He prevalence of low or impaired nutritional status among groups. Those prevalences are usually much lower than those estimated for at-nsk populations in dietary surveys using the RDAs as a basis for low intake. When both kinds of survey data coincide, identifying a group with high prevalence of a biochemical marker of abnormal nutritional status and with low dietary intake, we have strong evidence that a diet-related problem exists. However, we must consider the possibility that some other life-style factor or illness has contributed to the group's low nutritional status. REFERENCES FASEB (Federation of American Societies for Experimental Biology). 1984a. Assessment of the Iron Nutntional Status of the U.S. Population Based on Data Collected in the Second National Health and Nutrition Examination Survey, 1976-1980. Life Sciences Research Office. FASEB Special Publications Office, Bethesda, Md. FASEB (Federation of American Societies for Experimental Biology). 1984b. Assessment of Zinc Nutritional Status of the U.S. Population Based on Data Collected in the Second National Health and Nutrition Examination Survey, 1976-1980. Life Sciences Research Office. FASEB Special Publications Office, Bethesda, Md. Gallup Organization, Inc. 1982. Gallup Study of Vitamin Use in the U.S. Survey VI, volume 1. Gallup Organization, Inc., Princeton, N.J. Gunter, E. W., W. E. Turner, J. W. Neese, and D. D. Bayse. 1985. Laboratory Procedures Used by the Clinical Chemistry Division, Centers for Disease Control, for the Second Health and Nutrition Examination Survey (HANES II) 1976-1980. Public Health Service, Centers for Disease Control, Atlanta, Ga. Johnson, C., C. Woteki, and R. Murphy. 1984. Smoking, vitamin supplement use, and other factors affecting serum vitamin C. Fed. Proc. 43(3):666. McDowell, A., A. Engel, J. T. Massey, and K. Maurer. 1981. Plan and Operation of the Second National Health and Nutrition Examination Survey, 1976-80. Series 1, No. 15. DHHS Pub.
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NUTRITIONAL STATUS OF THE U.S. POPULATION 39 No. (PHS) 81-1317. Vital and Health Statistics. Public Health Service. U.S. Government Printing Office, Washington, D.C. NRC (National Research Council). 1980. Recommended Dietary Allowances, 9th ed. A report of the Food and Nutrition Board, Assembly of Life Sciences. National Academy of Sciences, Washington, D.C. USDA (U.S. Department of Agriculture). 1982. Food Consumption: Households in the United States, Spring 1977. Human Nutrition Infonnation Service, Consumer Nutrition Center, Report No. H-1. U.S. Government Printing Office, Washington, D.C. USDA (U.S. Department of Agriculture). 1983. Food Intakes: Individuals in 48 States, Year 1977-78. Human Nutrition Information Service, Consumer Nutrition Center, Report No. I-1. U.S. Government Printing Office, Washington, D.C. Welsh, S. O. 1984. Iron in U.S. diets. Speech to Washington, D.C., Nutrition Group, Wash- ington, D.C., September 26. Welsh, S. O., and R. M. Marston. 1983. Trends in levels of zinc in the U.S. food supply, 1909^ 1981. Pp. 15-30 in G. E. Inglett, ed. Nutritional Bioavailability of Zinc. American Chemical Society, Washington, D.C.
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Representative terms from entire chapter: