Multivitamins are poured from a bottle

Multivitamins are poured from a bottle Credit: AP

Supplements are big business; Americans buy more than $20 billion worth annually. But most of us have little evidence of whether they help, hurt or make no difference at all.

And what we don't know about supplements can hurt us. An American study to see whether vitamin E prevents prostate cancer discovered that, instead, it raises the risk of this disease. A Finnish study, meanwhile, has found that some supplements, particularly iron, are associated with an increased risk of death in older women.

If these new results make you think twice before taking supplements without a doctor's advice, that's just fine. As Jaakko Mursu, a co-author of the Finnish study, wrote in the Archives of Internal Medicine: "We see little justification for the general and widespread use of dietary supplements."

It would be nice to think that there's a magic pill, readily available in any shopping center, that will give us the gift of better health and longer life. And some supplements really are beneficial.

But for the most part, health and longevity are associated with eating right, exercising, shunning tobacco, drinking only a little, staying busy and connected to others, and getting adequate sleep. It helps to pick the right parents, of course, since genes matter a great deal as well.

As it turns out, "moderation in all things" is better advice than "take your vitamins," for the latter, we now know, are best consumed with a grain of salt.