Others have studied who uses dietary supplements and why. Again using data from the National Health and Nutrititon Examination Survey of 2007-10 that included 11,956 adults, Regan L. Bailey of the National Institutes of Health Office of Dietary Supplements and co-authors reported in 2013 these reasons given by the survey participants: 45 percent said they took them to “improve” and 33 percent to “maintain” overall health. Thirty-six percent of women took calcium for bone health and 18 percent of men took supplements for heart health or to lower cholesterol. Only 23 percent used supplements because a health care provider suggested they do so.

Perhaps most enlightening were the data on the characteristics of supplement users. In all probability, they were among the healthiest members of the population. They were more likely than nonusers to report being in very good or excellent health, to use alcohol moderately, to refrain from cigarette smoking, to exercise frequently and to have health insurance. Other studies have shown that supplement use is also more frequent among those who are older, who weigh less and have higher levels of education and socioeconomic status.

This means that in trying to determine possible health benefits of a supplement, researchers must control for all such characteristics in order to isolate the contribution of the supplement. Just looking at a large group of people, even following them for decades and finding that supplement users were healthier or lived longer, proves nothing if other influences on health and longevity are not taken into account.

Faced with equivocal or negative findings of health benefits from supplements, in 2013 the United States Preventive Services Task Force, an independent group of physicians who base their advice on solid evidence, opted not to recommend the regular use of any multivitamins to prevent cardiovascular disease or cancer in people who were not nutrient deficient.

All of which makes one wonder why people, myself included, opt to take one or more dietary supplements. Those who take a daily multivitamin/mineral supplement typically cite “nutritional insurance” as their rationale. Knowing that they often eat erratically or fail to consume recommended amounts of nutrient-rich vegetables and fruits, a supplement containing a broad range of vitamins and minerals seems the easiest and cheapest way to fill in any gaps.

But nutrition specialists point out that no pill can supply all the nutrients found in wholesome foods. For example, a multivitamin/mineral supplement contains none of the fiber in fruits and vegetables, and to provide the amount of daily calcium recommended (1,000 milligrams for adults, rising to 1,200 for women over 50 and men over 70), the combination pill would be too big for most people to swallow.