Soaring sales of supplements have scientists asking questions

Washington -- The millions of Americans who take a multivitamin and mineral pill each day aren't basing that decision on scientific evidence because there isn't any, according to a panel of nutritionists, biostatisticians and epidemiologists who met at the National Institutes of Health in mid-May to review the data on the safety and efficacy of such supplements for generally healthy people.

Plus, multivitamin users even might be causing themselves harm by unknowingly exceeding the upper safe limits of some vitamins, said the independent panel that gathered evidence from experts and members of the public for two days before compiling their findings in a report released May 17.

When all is said and done, according to the panel, there is little to support or reject widely held convictions that multivitamin tablets are important for good health.

They recommended that researchers mount vigorous studies to fill that void and that Congress expand the Food and Drug Administration's authority to tighten control over manufacturers.

"Half of American adults are taking multivitamins and minerals, and the bottom line is that we don't know for sure that they're benefiting from them. In fact, we're concerned that some people may be getting too much of certain nutrients," said panel Chair J. Michael McGinnis, MD, senior scholar with the Institute of Medicine.

Annual sales of supplements total about $23 billion, a substantial portion of which is spent on vitamins and minerals. Their increasing popularity often leads to confusion in physicians' offices over the pros and cons of their use by patients.

Although panelists were unable to shed much light on the use of multivitamins, they did provide a few recommendations for particular groups of patients. They advised that postmenopausal women take supplements of calcium and vitamin D for bone health; that antioxidants and zinc be considered for use by nonsmokers with early-stage, age-related macular degeneration and that women of childbearing age take daily folate to prevent neural tube defects in infants.

One problem in assessing health benefits arises because people who take vitamins are generally healthier than average to begin with, group members said. Consumers of vitamins often have healthier lifestyles and diets and a generally lower body mass index than nonconsumers. Use is also higher among women, the children of women who use vitamins, the elderly and those who have more education and higher incomes.

Ironically, the panel said, people least likely to take multivitamins are those who are more likely to have nutritional inadequacies and who stand to benefit the most.

Vitamin users are also in danger of inadvertently exceeding safe upper limits. So many foods are now fortified with vitamins and minerals that it is difficult to calculate just how much of a particular nutrient an individual is consuming, the panel reported. An estimated 65% of Americans used fortified foods or beverages last year.

The panel also examined available data on a few specific vitamins and minerals. They found that for beta carotene, for example, two large trials uncovered an increase in lung cancer among smokers and asbestos workers who took the vitamin but no preventive effect for a number of other cancers. Clinical trials testing vitamin E's protective value for cardiovascular disease found no decrease in death, although there was a decreased risk in prostate cancer among male smokers.

These findings may be part of a complicated story, noted Meir Stampfer, MD, DrPH, professor of epidemiology and nutrition at Harvard's School of Public Health, in testimony before the panel. Certain subsets of people, for example male smokers, may benefit from certain supplements, such as vitamin E, while others may not, he said.

It is particularly difficult to determine whether vitamins have any effect on cancer, he told the panel, because of the long time it takes for the disease to develop.

Irwin Rosenberg, MD, senior scientist and professor at the Jean Mayer Human Nutrition Research Center at Tufts University in Boston, decried the lack of a definition for multivitamins which differ in content and dose. "Good research requires good nomenclature, and that doesn't exist in vitamins," he said. For purposes of their review, the panel defined multivitamins and minerals as any supplement containing three or more vitamins and minerals.

The dietary supplement industry's trade association, the Council for Responsible Nutrition, took issue with some of the panel's findings. While agreeing with the recommendation that adverse events should be reported to the FDA, the group also pointed to the benefits of a daily multivitamin in promoting good health.

"For millions of Americans who struggle with diet and nutrition, a daily multivitamin provides a safe, affordable and reliable means of filling nutrition gaps and promoting overall good health," said CRN President and CEO Steven M. Mister.