Studies Fail To Confirm Benefits Of Vitamin Supplements

Lowly vitamins were some of the most promising medicines of the 1990s, wonder pills that appeared to fight cancer, heart disease, strokes and other ailments.

Laboratory tests and initial studies in people suggested they could play a crucial role in preventing some of the most intractable illnesses. The National Institutes of Health invested hundreds of millions of dollars in elaborate clinical trials designed to quantify their disease-fighting abilities.

As the results of those trials roll in, however, nearly all fail to show any benefits of taking vitamins and minerals. Two long-term trials of more than 50,000 participants offered fresh evidence that vitamin C, vitamin E and selenium supplements don't reduce the risk of prostate, colorectal, lung, bladder or pancreatic cancer. Other recent studies have found that over-the-counter vitamins and minerals offered no help in fighting strokes, other cancers or cardiovascular disease.

Research has even suggested that, in some circumstances, vitamin and mineral supplements can be unsafe. Some physicians now advise their patients to rely instead on a healthy diet to provide needed vitamins and minerals.

"These things are ineffective, and in high doses they can cause harm," says Dr. Edgar R. Miller, a medical professor at Johns Hopkins University School of Medicine. "People are unhappy with their diets, they're stressed out, and they think it will help. It's just wishful thinking."

Faith in vitamins runs deep. The Council for Responsible Nutrition, a Washington, D.C.-based trade group, estimates that 64 percent of American adults take vitamin and mineral supplements. Despite the steady drumbeat of reports questioning their efficacy, sales have risen from $5 billion in 1995 to $10 billion this year, says the Nutrition Business Journal.

Scientists remain certain that vitamins are essential to health. They have puzzled, however, over how their obvious benefits could be so elusive in randomized controlled trials, the gold standard of medical research.

Unlike observational studies, which look backward at groups of people to identify factors that are associated with a particular disease, a forward-looking randomized controlled trial has the power to show that a particular factor can prevent the disease.

The studies rely on thousands of participants who are randomly assigned to receive a medicine or an identical-looking dummy pill. Researchers carefully track the participants so they can account for other factors that might affect health outcomes, such as age, diet and amount of physical activity. After several years, the researchers compare the number of people in each group that developed a particular disease and use statistical tools to see whether the medicine made a difference.

Los Angeles Times