When it comes to dietary supplements, in some ways we haven't come very far from the days of the traveling medicine shows.
The Food and Drug Administration does not analyze the content of these substances, which range from vitamin pills to exotic herbal elixirs, before they're allowed on the market. The agency leaves it up to the manufacturers to ensure their products are safe and do what they claim.
Once on the market, if a dietary supplement is found lacking or dangerous, the FDA can take action against manufacturers and distributors.
To add to the gamble, medical experts disagree on the benefits of many supplements. Recent medical research has not been kind to supplements, although a rigorous new study did find that taking B vitamins can prevent age-related macular degeneration in women.
"If you have a well-balanced diet with vegetables and fruit, you can get all these vitamins and meet the recommended daily allowance," says Dr. Kevin B. Sneed, assistant dean and clinical director of clinical pharmacy at the University of South Florida College of Medicine. But given that many of us don't have a well-balanced diet, he sees a multivitamin as a dietary insurance policy.
Whatever you take, you should first check with your doctor, according to the National Institutes of Health Office of Dietary Supplements. Some substances interfere with prescription medications, and some can be dangerous to certain individuals.
Multivitamins: Recent studies conclude that multis don't prevent cancer, as once was thought. But a good one is worth taking if you eat a typical American diet with lots of processed food and don't get the recommended daily allowance of vitamins and minerals, says USF's Sneed.
Calcium and vitamin D: Many researchers believe calcium citrate with vitamin D helps keep bones strong. Vitamin D is essential for the body to absorb calcium, but if you limit sun exposure to avoid cancer, you've blocked a key source of D. Do not take iron or zinc at the same time as calcium, which blocks absorption of those nutrients. Separate the doses by an hour or two, Sneed says.
The B vitamin complex, which includes B-1, B-6 and B-12, helps keep the nervous system and eyes healthy, build red blood cells, aid in digestion and appetite and helps people maintain energy, according to the National Institutes of Health. A new study published Monday in the Archives of Internal Medicine found the B vitamins help prevent age-related macular degeneration in older women.
Omega 3, a fatty acid found in fish oil and flaxseed, appears to have a beneficial effect on the cholesterol panel, especially on triglycerides, Sneed says. But be careful about the purity of fish oils. (Go to the Environmental Defense Fund Web site at www.edf.org and type "omega-3 brands'' in the search field. Click on the first listing for recommendations.)
Glucosamine, a substance said to reduce arthritis pain, does appear to work over time, Sneed says. He recommends a 1500 mg daily dose and says it takes two to three months before benefits are evident.
Many people take vitamin C to prevent colds, but most research finds little evidence that it does.
Several studies suggest there is no proof that echinacea prevents or treats colds, though there is some indication that it may slightly lessen the severity of upper respiratory infections.
Research is sketchy on whether vitamin E helps prevent heart attacks.
St. John's wort has been shown to be no more effective than a placebo in treating major depression, though some studies indicate it may be useful against mild depression.
Timed-release vitamins appear to be no more beneficial than standard multivitamins, according to a National Academy of Sciences study.
May do harm
Overdosing on vitamin E can cause bruising. The vitamin thins the blood, so people already taking blood-thinning medicines should check with their doctors before taking it.
In large amounts, garlic — a popular supplement — also thins the blood, as does ginkgo.
Iron is an important supplement for women of child-bearing age, but men who take too much have an increased risk of heart attack. Excessive iron also is a hazard for children.
Megadoses of vitamins can damage your health. Especially dangerous are high doses of the fat-soluble vitamins, such as A, D, E and K, because they accumulate in the body.
Sources: National Institutes of Health, MedicineNet.com, WebMD.com and USF's Dr. Kevin B. Sneed