High doses of beta carotene and folic acid could be harmful.


By TARA PARKER-POPE

Ever since the Nobel Prize-winning biochemist Linus Pauling first promoted“megadoses”of essential nutrients 40 years ago, Americans have been devoted to their vitamins. Today about half of all adults use some form of dietary supplement, at a cost of $23 billion a year.

But are vitamins worth it? In the past few years, several high-quality studies have failed to show that extra vitamins, at least in pill form, help prevent chronic disease or prolong life.

The latest news came February 9 after researchers in the Women’s Health Initiative study tracked eight years of multivitamin use among more than 161,000 older women. Despite earlier findings suggesting that multivitamins might lower the risk for heart disease and certain cancers, the study, published in The Archives of Internal Medicine, found no such benefit.

Last year, a study that tracked almost 15,000 male physicians for a decade reported no differences in cancer or heart disease rates among those using vitamins E and C compared with those taking a placebo. And in October, a study of 35,000 men dashed hopes that high doses of vitamin E and selenium could lower the risk of prostate cancer.

Of course, consumers are regularly subjected to conflicting reports and claims about the benefits of vitamins, and they seem undeterred by the news - to the dismay of some experts.

“I’m puzzled why the public in general ignores the results of well-done trials,”said Dr.Eric Klein, national study coordinator for the prostate cancer trial and chairman of the Cleveland Clinic’s Glickman Urological and Kidney Institute.“The public’s belief in the benefits of vitamins and nutrients is not supported by the available scientific data.”

Everyone needs vitamins, which are essential nutrients that the body can’t produce on its own. Inadequate vitamin C leads to scurvy, for instance, and a lack of vitamin D can cause rickets.

But a balanced diet typically provides an adequate level of these nutrients, and today many popular foods are fortified with extra vitamins and minerals. As a result, diseases caused by nutrient deficiency are rare in the United States.

In any event, most major vitamin studies in recent years have focused not on deficiencies but on whether high doses of vitamins can prevent or treat a host of chronic illnesses. While people who eat lots of nutrient-rich fruits and vegetables have long been known to have lower rates of heart disease and cancer, it hasn’t been clear whether ingesting high doses of those same nutrients in pill form results in a similar benefit.

In January, an editorial in The Journal of the National Cancer Institute noted that most trials had shown no cancer benefits from vitamins- with a few exceptions.

But some vitamin studies have also shown unexpected harm, like higher lung cancer rates in two studies of beta carotene use. In 2007, The Journal of the American Medical Association reviewed mortality rates in randomized trials of antioxidant supplements. In 47 trials of 181,000 participants, the rate was 5 percent higher among the antioxidant users.

Scientists suspect that the benefits of a healthful diet come from eating the whole fruit or vegetable, not just the individual vitamins.“There may not be a single component of broccoli or green leafy vegetables that is responsible for the health benefits,”said Dr.Peter H.Gann, professor and director of research in the department of pathology at the University of Illinois in Chicago.“Why are we taking a reductionist approach and plucking out one or two chemicals given in isolation?”