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a Departments of Public Health Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina
b Departments of Family and Community Medicine, Wake Forest University School of Medicine, Winston-Salem, North Carolina
Sara A. Quandt, Department of Public Health Sciences, Medical Center Boulevard, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1063 E-mail: squandt{at}wfubmc.edu.
William B. Ershler, MD
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Abstract |
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Methods. Data are from a population-based sample of 130 community-dwelling adults aged 70 years and older in two rural North Carolina counties. The sample was 34% African American, 36% European American, and 30% Native American. Interviewer-administered semiquantitative food frequency questionnaires were used to obtain data on usual diet and supplement use. In-home interviews allowed verification of supplement composition. Intakes from diet and supplement products were examined for vitamins A, E, B6, C, folate, iron, zinc, and calcium.
Results. Of those who participated in the study, 47% reported using one or more supplement products. African Americans were significantly less likely to take supplements than Native Americans or European Americans. Based on dietary intakes, 65% of the participants were deficient (<2/3 recommended dietary allowance [RDA]) for at least one nutrient. The use of supplement products for the eight nutrients investigated was not related to dietary nutrient deficiency. For all nutrients investigated, except iron and calcium, a greater proportion of those without dietary deficiency took a supplement product than those with deficiency. Using logistic regression, ethnicity (European American and Native American), and gender (women) were significant predictors of supplement use.
Conclusions. These findings suggest that although both dietary deficiencies of vitamins and minerals and supplement use are relatively high in this population, there is no association between supplement use and deficient dietary intakes for the eight nutrients examined. Health care providers should be aware that nutritional counseling and guidance on appropriate supplement usage is needed in this population.
VITAMIN and mineral supplement products are widely consumed by older adults in the United States. Depending on the population studied, rates of usage range from 26% to 80% (1)(2). Most studies have reported that supplement use is more frequent among women, the well-educated, the typically healthy, and those who have higher incomes (3)(4). Because most studies have been small, there has been limited examination of ethnic variation in supplement use. When ethnicity has been studied, research has found elderly minority persons less likely to use vitamin and mineral supplements (5)(6)(7).
The dietary requirements of adults change as they grow older, placing older adults at nutritional risk because of a decreased need for energy, but a constant or even increased need for some vitamins and minerals (8). Vitamin and mineral supplements provide a means of ensuring adequate intakes of such nutrients, but few studies have examined their usage in terms of nutritional risk. That is, are supplement users consuming supplement products to correct inadequate intakes from food? Because most supplement users take supplements on individual initiative rather than physician advice (9), it is likely that supplement use is not based solely on nutritional risk.
Older rural adults have been recognized as a group at possible risk for health and nutritional problems. As a whole, rural adults have lower levels of education, lower incomes, and problems accessing health care because of issues of distance, transportation, and limited health care options. All of these reasons, plus limited grocery store options, more expensive groceries at those stores, and reduced ability to engage in home food production with advancing age, may place older rural adults at particular risk for nutrient deficiencies (10).
This study responds to some of these shortcomings in existing studies by focusing on supplement use in a multiethnic population in a rural area with a moderately high rate of poverty. The purpose of the study is as follows: (i) describe supplement product use by ethnicity, gender, and other selected demographics among older rural adults living in North Carolina; (ii) relate supplement usage to adequacy of nutrient intake from diet; and (iii) determine predictors of degree of supplement usage in this population.
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Methods |
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Data Collection
Data were obtained in face-to-face interviews conducted in participants' homes. In a few cases, participants chose to be interviewed at another location, usually a senior center. Demographic and personal data included gender, ethnicity, age, marital status, tobacco use (smokeless and smoked), weight, chronic conditions, and number of prescription medications. Weight was measured using a professional quality portable scale (Health O-Meter, Bridgeview, IL).
Dietary data collection was designed to measure usual dietary intake over the preceding year. Data were collected using the semiquantitative food frequency questionnaire (FFQ) component of the National Cancer Institute Health Habits and History Questionnaire (14). The version used had been modified to improve ethnic food choices and validated (15). The FFQ has been validated for use in an older population and was used to assess dietary intake for the Third National Health and Nutrition Examination Supplemental Nutrition Survey of Older Americans (16)(17).
Specific steps were taken to overcome known problems of underreporting on FFQs (17). Interviewers attended a training session devoted to FFQ dietary data collection and completed practice interviews. The FFQ was interviewer-administered with response categories printed in large font on cue cards to assist respondents. Interviewers used standard techniques that included extensive probing to obtain complete data (17). FFQ administration took 30 to 60 minutes. Interviewers were knowledgeable about local food preparation and consumption patterns, which increased their ability to interpret local food names and probe for appropriate condiments and preparation techniques. The data collected were analyzed using the DietSys software package (National Cancer Institute, Bethesda, MD) (17). Quality assurance procedures included double-entry of all data and edit checks for extreme values.
As part of the FFQ, participants were asked if they took any vitamin or mineral supplements during the past month. The assumption was made that the 1-month intake pattern was applicable for the whole year. Because interviews took place in the home, interviewers were able to document the type, brand, and composition of supplements taken. Data were collected on frequency of supplement usage (pills per day, week, or month) and dosage per pill. Eight vitamins and minerals were assessed in the analysis presented here: calcium, iron, zinc, folate, and vitamins A, C, E, and B6. Intake for these was calculated from all supplements reported, including combination supplements (e.g., multivitamins) and single nutrient supplements.
Measures
Three measures of daily intake were created for each participant for each of the eight nutrients of interest. Dietary intake of each vitamin or mineral was calculated from the food items of the FFQ, supplement intake was calculated from the vitamin and mineral supplement items of the FFQ, and total intake was obtained by summing the dietary and supplement intakes. Participants were considered deficient for a particular nutrient if their dietary intake for that nutrient was less than 2/3 of the recommended dietary allowance (RDA) for persons aged 51 years and older. Participants were coded as supplement users if they reported any vitamin or mineral supplement usage, and supplement nonusers if they reported no supplement usage. To assess the degree of supplementation, the number (0 to 8) of nutrients obtained through supplements was calculated for each participant.
Data Analysis
Chi-square tests were used to assess the association of deficiency and supplement use with the participant's demographic characteristics. Logistic regression was used to assess which characteristics were jointly predictive of deficiency and supplement use. Age, weight, gender, ethnicity, marital status, number of chronic conditions, and number of prescription medications were included in the model. A backward-stepping algorithm was used to remove nonsignificant factors from the model. Regression techniques were then used to assess which factors were predictive of the degree of supplementation. The significance level used was p < .05.
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Results |
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Nutrient intake, dietary deficiency, and supplement product use are shown in Table 2 . There was considerable variation by nutrient in the number of participants with deficient dietary intakes, ranging from 0% for folate to 60% for zinc. Eighty-four participants (65%) were deficient in at least one of the eight nutrients; 23 (18%) were deficient in one, 33 (25%) in two, 13 (10%) in three, 9 (7%) in four, 2 (2%) in five, and 4 (3%) in six nutrients.
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Table 3 shows supplementation of each nutrient by dietary deficiency status of participants. Supplement use was not related to dietary deficiency. Indeed, for six of the eight nutrients (vitamin A, vitamin E, folate, vitamin B6, vitamin C, iron, and zinc), a greater percentage of participants who were not deficient supplemented that nutrient than those who were deficient. For example, 38% of participants consuming an adequate amount of zinc in their diets supplemented zinc compared with only 21% of those whose dietary levels were deficient.
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Conclusions |
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Ethnicity was strongly associated with supplement use, with African Americans significantly less likely to use supplements than any other group. Further study is necessary to understand why this is the case and why European Americans and Native Americans are similar in usage. It is possible that there is greater emphasis on preventive health behaviors among these groups. Previous studies in the general adult population have shown that supplement use is associated with such behaviors as active lifestyle, not smoking, and cancer screening (4)(18).
This study goes beyond previous studies of older adults to examine vitamin and mineral supplement usage in the context of dietary intakes. These results indicate that there is little association between dietary deficiency and supplementation for the eight nutrients examined. Those persons taking supplements are more likely to have adequate diets for these nutrients than those who do not. This leads to the speculation that both diet and supplementation behaviors reflect similar knowledge and beliefs about health promotion, rather than attempts to compensate for dietary deficiencies. In other studies of the general adult population, supplement users have been found to consume more fruits, vegetables, and dairy products (4)(18).
Only a subset of nutrients essential for health and functioning was examined in this study. Yet even with this small group of nutrients, 65% of all participants had diets that were deficient in one or more nutrients, highlighting the difficulty these older adults have in planning, obtaining, or consuming a nutrient-dense diet. Although recommending vitamin and mineral supplements remains a controversial topic (17)(18), vitamin-mineral supplementation may be the best way for this group to get the nutrients they need if they are unable to consume a well-balanced diet (19)(20).
This study used the most recent recommended dietary allowances (RDAs) as a reference standard for evaluating dietary intakes (21). These will eventually be replaced by the dietary reference intakes (DRIs), which are currently under development. The DRIs will provide estimates of nutrient needs based on more current research and expand the focus of recommendations from deficiency diseases to long-term health, including chronic disease (22)(23). They were not used in the present study because they are not yet available for all nutrients and some are only available in prepublication form. Examining the DRIs proposed for some nutrients, however, shows that the present study presents a very conservative estimate of vitamin and mineral deficiency in this rural population. For example, the DRIs will recommend an increase for folate to 400 µg of dietary folate equivalents in the daily reference standard for adults within the age range of our study participants. Had this figure been used in these analyses, 34% of the elderly persons studied would have been considered deficient in folate, compared with 0% using the current RDAs. Similarly, the DRIs will recommend an increase in the daily reference standard for older adults for calcium to 1200 mg. Had this figure been used, 61% rather than 24% of the elderly persons studied would have been considered deficient in calcium. Thus, the use of the DRIs in future research will likely classify even more older adults as deficient for those nutrients most closely associated with chronic disease and disease prevention.
The present study collected cross-sectional supplement use data. More accurate assessment of supplement use can be obtained in longitudinal designs (24), and these should be the focus of future research. The use of biomarkers of nutritional status would further strengthen future studies by providing a means to verify nutrient excesses and deficiencies. Regardless of the limitations of the present study, its findings indicate that vitamin and mineral supplement products are frequently used by rural adults, but intake is related to gender and ethnicity, not dietary deficiency. Health care providers should be alert to this and counsel their patients accordingly.
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Acknowledgments |
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Received June 23, 1999
Accepted January 24, 2000
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