We’re Very Supplemented

Most U.S. adults don’t depend solely on food for their nutrition, a new government study finds. Increasingly, men and women reach for pills—vitamins, minerals, and other commercial supplements—to insure against the possibility they’re not eating a healthy diet.

Researchers collected data on supplement taking during 1999 and 2000 from participants in the National Health and Nutrition Examination Survey. This is one of a long-running series of federal surveys of diet and health patterns in a cross-section of the U.S. population. To ensure that it characterizes even traditionally underrepresented segments of society, the survey oversamples some groups—lower-income people, Mexican Americans, and elderly people, for example. Analysts then recalculate results from these groups to account for their share of the population, based on census data.

Whereas 3 decades ago only 23 percent of adults augmented their diets with vitamins and other encapsulated nutrients, that total has climbed to 52 percent now. However, Kathy Radimer and her colleagues at the National Center for Health Statistics, a division of the Centers for Disease Control and Prevention, find that wide demographic variability exists in supplementation patterns.

For instance, people with at least some college education are more than twice as likely as high-school dropouts to take supplements. They’re even 70 percent more likely than high-school graduates to take multivitamins and vitamin E, nearly twice as likely to take vitamin C or B-complex vitamins, and about 50 percent more likely to take calcium.

The researchers also uncovered trends in people taking a host of less traditional supplements, from single nutrients, such as folate, to herbal products, such as ginkgo and echinacea. Most such herbs have no nutrient value, but they’re consumed because of their putative health-promoting properties.

“There’s no official definition for supplements,” Radimer explains, so categorizing them as either a supplement or food has become “tricky.” Moreover, she notes, with the growing trend toward foods with medicinal or healthful properties (see The Rise of Nutraceuticals), “the line between dietary supplements and foods or drinks is becoming very unclear.”

For instance, when tallying supplements, her group ignored herbal teas, even though they sometimes contain the same ingredients as in powdered or encapsulated herbal preparations that did qualify as supplements in the survey. “We also discounted [as supplements] most of the sports drinks,” Radimer notes, “even though they do contain a lot of vitamins and minerals.”

Her team details its findings in the Aug. 15, 2004, American Journal of Epidemiology.

Vitamin popping

The good news, Radimer’s team says, is that a large share of adults now gets at least “adequate” amounts of many important vitamins and minerals. In fact, the data show, supplements may actually be pushing some people toward unhealthy excesses of certain nutrients, especially if they routinely down multivitamins in addition to high-dose single-nutrient pills or antacids.

Some antacids, in fact, contain quantities of magnesium approaching the National Institute of Medicine’s recommended upper limit. Exceeding that limit can lead to diarrhea and other problems. More typically, however, antacids contain large quantities of calcium. Although that should be good for bones, Radimer notes that “there have been some studies linking calcium supplements with prostate cancer.”

Studies attempting to correlate diet and health have typically done a poor job at quantifying the contribution of supplements, says Radimer. That’s understandable, she adds, because of the blurred line between supplements, foods, and drugs.

Indeed, some of the people in the new study weren’t aware of the extent of their supplementation, reporting some supplements, such as iron tablets and vitamins taken during pregnancy, as prescription medicines. Such misidentifications “could contribute to underreporting in studies of supplement use,” Radimer’s group notes.

When supplements act up

Another issue addressed by the study is the potential for interactions between prescribed drugs and unreported or underreported supplements. Although rare, these interactions occasionally prove serious, says Bill J. Gurley of the University of Arkansas for Medical Sciences in Little Rock.

For instance, many people take garlic supplements because preliminary studies have suggested that they might protect the heart or fight cancer (see Garlic’s Benefits: It’s All in the Preparation). However, the pharmaceutical scientist observes that, by chemically interacting with a drug, certain enzymes in garlic can effectively strengthen the drug beyond its prescribed dose. On the other hand, in at least one study, garlic supplements substantially undercut the effectiveness of an HIV drug (SN: 1/5/02, p. 8).

St. John’s wort, an herb used chiefly to treat depression (SN: 4/21/01, p. 244), not only impaired sperm in test-tube studies (SN: 3/27/99, p. 207), but has also diminished the efficacy of at least one cancer drug (SN: 4/20/02, p. 254). Compounds in the plant and supplements made from it can affect the activity of enzymes responsible for metabolizing some 50 to 70 percent of all conventional medications, observes Gurley. So when people take St. John’s wort, he says, “there’s a tremendous likelihood for a drug interaction.”

The hidden significance of those interactions was driven home to him a few years back when several transplant patients taking St. John’s wort rejected their organs. Gurley observed that “concentrations of the immunosuppressive drug cyclosporine were just plummeting” in patients taking the herbal supplement, even as doctors increased doses of the drug.

“This was before we really knew all that much about St. John’s wort,” or at least its chemistry, Gurley explains. When it became clear that what the problematic transplant patients had in common was their use of a common herbal supplement, “we immediately told them to stop taking it.”

Some other supplements can contain toxic metals, such as the lead in some calcium pills (SN: 3/31/01, p. 205). But lead isn’t the only risk. Gurley’s analyses of the now-banned ephedra supplements used as weight-loss aids until this year, found that many carried mercury, cadmium, arsenic, and even uranium.

And in some cases, dietary supplements may themselves prove toxic. Indeed, Amy Christine Brown of the University of Hawaii has been archiving reports of adverse health events linked to herbal products. She maintains her findings on her Web site in a Harmful Herb List (http://www2.hawaii.edu/~amybrown/).

The bottom line, Radimer and her colleagues conclude, is that supplement taking is getting common enough in the United States that researchers can no longer afford to ignore people’s regular ingestion of pills, powders, and other nonfood sources of nutrients. Researchers who do so risk skewing their interpretations of the influence of diet on health.

The hard part of understanding the effects of supplements, she says, will be quantifying the contributions of so many of them now in use. Moreover, her group found, intake patterns vary substantially by age, gender, income, education, and even race. Overall, however, the new data indicate that people taking multivitamin supplements have been doing so daily for years.