Factors Associated With the Intake of Dietary Supplements - Statistical Data Included

Family Economics and Nutrition Review,  Wntr, 1999  by Rodolfo M. Jr. Nayga,  Debra B. Reed

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Research on the relationship between diet and disease has increased interest in nutrition and in determining the nutrients and their levels that are related to adequate health (7). The latest report on nutrition monitoring of the U.S. population classifies the dietary intake of iron and calcium as current public health issues (4). This classification signifies an inadequate intake across many age, gender, and ethnic groups, and there is associated biochemical, clinical, or anthropometric evidence of adverse health conditions. Regarding intake, other minerals (e.g., magnesium, potassium, zinc, and copper) and vitamins (e.g., A, C, E, [B.sub.6], and [B.sub.12]) are considered potential public health issues for which further study is required.

While no dietary supplement can replace a healthful diet, experts agree that providing the body with adequate nutrient intake is especially important in light of the increasing prevalence of degenerative diseases: for example, heart disease, cancer, and osteoporosis (21). Because of increasing awareness and knowledge about the link between nutrition and health, as well as the rising costs of healthcare, many Americans are embracing self-medication with dietary supplements aimed at preventing diseases (11). Evidence has been accumulating that a variety of dietary components may have a protective effect against cancer; therefore, many argue that supplements are necessary--because they extend beyond the prevention of deficiency diseases to the prevention of chronic diseases such as cancer (14). For example, the possible protective effects against certain diseases of several nutrients, especially vitamins C and E and beta carotene, have been well publicized (13).[1]

Consequently, public interest in dietary supplements has been intense. The Council for Responsible Nutrition reported a 19-percent increase in retail sales of supplements between 1987 and 1992 and estimated that about 40 to 50 percent of the U.S. population uses vitamin and mineral supplements (18). According to the American Dietetic Association 1997 Nutrition Trends Survey, 35 percent of Americans believe vitamin supplements are necessary to ensure proper health, an increase from prior surveys (28 percent in 1995 and 27 percent in 1993 and 1991) (2).

Despite the popularity and potential benefits of dietary supplements, few studies have examined the effect of sociodemographic, lifestyle, and attitudinal factors on the intake of dietary supplements. Using the 1992 National Health Interview Survey, researchers found that demographic and lifestyle characteristics and the diet of supplement users are typical factors associated with low risk of chronic disease (18). Analyzing the National Health and Nutrition Examination Survey (NHANES) II data collected between 1976 and 1980, other researchers found that supplement use was more common among women, Whites, older persons, and those with more years of education and higher income (10).

Stewart et al. (19) and Subar and Block (20) found that supplement use was most common in the western United States and among whites, women, older persons, those with higher incomes, those with higher education, and nonsmokers. Kolasa, Lackey, and Poehlman (9) found that special diet and attitudinal variables, such as an individual's willingness to make needed dietary changes, influence the intake of vitamin supplements. A review of research on the effects of exercise on vitamin status revealed that vitamin supplementation continues to be widely practiced by athletes in an effort to deal more readily with the rigors of training (3).

Most of these studies have also disclosed the positive correlation between vitamin supplement intake and more healthful diets. These studies, however, used older data sets when dietary supplements were not as popular. Thus the findings may no longer represent current conditions. The intense scientific and popular interest in recent years in dietary supplements has increased the need for more current information on factors affecting individual supplement use. The objective of our study is to better understand the relationships between sociodemographics, lifestyle characteristics, and a number of attitudinal factors and the intake of dietary supplements.

Methods

We hypothesized that the likelihood of taking dietary supplements is a function of income, race, gender, urbanization, whether the individual is a food stamp recipient, whether the individual is pregnant or lactating, age, employment status, household size, education, body mass index (BMI), the individual's perception of own health, special diet status, whether the individual smokes, degree of exercise, number of television hours, a nutritional knowledge factor, a diet-disease variable, and a belief about diet factor. Therefore, our empirical model is specified as follows:

Suppl = [f.sub.i] (income, Black, other, age,
        city, nonmetro, fstamp, preglact,
        male, unemployed, hhsize,
        grade, BMI, health, specdiet,
        smoke, know, disease, belief,
        exercise, tvhours).