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Supplementing Your Diet: Vitamins, Minerals and Beyond

NIH | Nov 17, 2014, midnight

The world of dietary supplements is getting more and more complicated. People aren't just taking vitamins and minerals anymore. Now, things like glucosamine, saw palmetto, black cohosh and ginkgo biloba are crowding onto shelves beside old standbys like vitamin C, calcium and iron. How do you sort through it all?

Dietary supplements include a broad range of vitamins, minerals, herbs and other substances meant to improve upon your diet. They can come as pills, capsules, powders and liquids.

The U.S. Food and Drug Administration, which regulates dietary supplements, treats them more like foods than like drugs. Dr. Paul M. Coates, director of NIH's Office of Dietary Supplements (ODS), says, "Dietary supplements are generally regarded as safe based on a long history of human use, unless proven otherwise. By contrast, drugs are not assumed to be safe until extensive testing has been done to prove their safety."

Supplements can play an important role in your health. Some doctors advise patients to take a multivitamin-mineral supplement to make sure they're getting enough of all the nutrients they need. While this may provide some insurance, Carol Haggans, a consultant with ODS, cautions, "People shouldn't feel they can make up for an unhealthy diet by taking a multivitamin-mineral supplement." A combination of all the vitamins and minerals together in foods provide the greatest health benefit, she says. "In general, if you eat a healthy diet, you shouldn't need to supplement it with extra nutrients."

However, some people might need more of certain nutrients. Doctors often advise women of child-bearing age to take folic acid, for example. Many people don't get enough calcium. According to some surveys, 44% of boys and 58% of girls age 6-11 don't get enough-and the numbers get even higher as people age. It's probably best to eat 2-3 servings per day of calcium-rich foods like dairy products. But if you have trouble eating dairy products because they upset your stomach and you don't get enough calcium in other foods, a supplement might help.

Since some supplements may help you, it's easy to go a step farther and think that taking more would be even better. This can cost a lot and may not provide the benefit you expect. It can also be risky.

"Almost all of the nutrients have tolerable upper intake levels-the amount it's recommended you stay under each day," Haggans says. Amounts above these levels can be toxic. Too much vitamin A, for instance, can cause birth defects, liver problems, weak bones and nervous system disorders. Too much calcium can cause kidney problems and block your ability to use other minerals in your diet.

NIH has several studies under way to look at whether high doses of certain supplements can prevent disease. For example, NIH's National Cancer Institute is funding the Selenium and Vitamin E Cancer Prevention Trial (SELECT) to see if selenium and vitamin E can help prevent prostate cancer. But this isn't an area you should experiment in by yourself.

Dr. Coates explains that, for the most part, supplement "megadoses" haven't been tested. "Absence of evidence of harm isn't the same as evidence of absence of harm," he says. "In many cases we just don't know."

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