supplements regularly or occasionallyup from 39% in 1977 (USDA, 1987b). Of the survey's low-income women 19 to 50 years of age, 45% took supplements during 1986 (USDA, 1987a).
The most comprehensive survey of dietary supplement use in the United States was conducted by the Food and Drug Administration (FDA) in 1980 through telephone interviews with 2,991 representative Americans over 15 years of age (Stewart et al., 1985). The FDA found that 35.9% of the men and 43.8% of the nonpregnant, nonlactating women consumed supplements daily. The supplement users were grouped into four categories: light users (who on average consumed the equivalent of 70% of the RDA for each nutrient), moderate users (168% of the RDA), heavy users (400% of the RDA), and very heavy users (777% of the RDA) (Levy and Schucker, 1987). The majority of the users took only one nutrient or combination product, although 10.9% of the sample consumed from 5 to 14 separate products (Stewart et al., 1985). Dietary supplement use was most prevalent in the western United States and among Caucasian people with relatively high incomes and at least a high school education.
The FDA investigators also noted that specialized vitamin and mineral preparations were most commonly taken by the heavy and very heavy users (28% and 14% of all users, respectively). The light and moderate users (42% and 16% of all users, respectively) favored the broad-spectrum, multinutrient products (Levy and Schucker, 1987). Compared to light and moderate users of dietary supplements, heavy and very heavy users were more likely to shop in health food stores, buy supplements through the mail, read specialized health literature, believe they had personal control over their health, engage in daily exercise, avoid involving their physicians in their decisions about supplements, and perceive specific rather than general health benefits from their supplements. The FDA investigators described the light and moderate users as people who consume supplements as insurance against dietary deficiencies. They described heavy and very heavy users as those who take supplements as part of an active effort to achieve better health.
Fairly high rates of dietary supplement use were also found in earlier national surveys conducted for the FDA. In 1969, 27% of the adults surveyed had taken a supplement on the day of the interview, and 57% of the sample said they had taken supplements at some time (National Analysts, Inc., 1972). Subjects most commonly took supplements to improve health, to obtain ''more pep and energy," to prevent colds, to reduce their risk of becoming ill, and to remain healthy while dieting. In 54% of the households contacted in 1973, at least one family member took supplements. The most frequent user was the homemaker (usually female), followed by the spouse and preteen child (FDA, 1974). In a similar study conducted in 1975, 47% of the households contained at least one member who took supplements. Again, the most frequent user was the female homemaker (FDA, 1976). The extent of dietary supplement use in the United States during the late 1970s was determined by Koplan et al. (1986), who evaluated data from the National Health and Nutrition Examination Survey (NHANES II). They found that 21.4% of adults in the United States took supplements daily and that another 13.5% took them at least once a week. Higher rates of supplement use were associated with women, whites, older age (ages 51 to 74 compared to ages 18 to 50), higher incomes, higher educational levels, and higher nutrient intakes from food.
Schutz et al. (1982) found that 67% of 2,451 randomly selected adults surveyed in seven western states took supplements over a 2-year period. Multiple vitamins with or without iron, vitamins C and E,. and the B complex vitamins were most commonly taken. The most frequently given reasons for taking supplements, selected from a list provided by the investigators, were "to prevent colds and other illnesses," "to give me energy," and "to make up for what is not in food." Factors found to be significantly associated with supplement use included age (higher use at younger ages), education (greater use at higher educational levels), sex (women were heavier users), and the perception that the nutritional quality of food had decreased over the past decade. When a subsample of 689 people was questioned further, 59% of the users reported that their supplements were of "some benefit" to their health, and another 34% found them to be of "great benefit" (Read et al., 1985). In a study of a subsample of 1,673 people, differences were found between those who took multivitamins/minerals and those who took individual supplements of either vitamins A, C, or E in the importance placed on the need for supplementation and where nutrition information was obtained (Read et al., 1987). Users of one of these nutrients were significantly more likely than users of multivitamins/minerals to have a lower opinion of today's food quality, to classify their diets as being either poor or very poor, to believe in the