Dietary Supplements: Can You Separate Fact from Fiction?
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Dr. John Swartzberg is an internist and specialist in infectious disease and is chair of the editorial board of the UC Berkeley Wellness Letter and berkeleywellness.com. He is also a clinical professor emeritus of medicine at the University of California, Berkeley School of Public Health and the University of California, San Francisco School of Medicine. He contributed this article to Live Science's Expert Voices: Op-Ed & Insights

Dietary supplements have captured the imaginations of many Americans. More than half of Americans take at least one dietary supplement, mostly multivitamins. In total, people in the United States spend about $28 billion on vitamins and other supplements each year. So, it's no surprise that people often ask me: Which ones work? Are they safe? Are they worth the money?

There are hundreds of different supplements, and no simple answers about the benefits of most of them because there is very little science to support manufacturers' claims. Much of what we think we know is myth, and is not supported by research. Here are some facts to help you make an informed decision about the supplements you put into your body. See if you can separate the myths from the facts.

1. Supplements are regulated like drugs, and those sold on drugstore shelves have been approved by the U.S. Food and Drug administration (FDA).

Myth. Supplements are not regulated or tested like drugs. Drugs must be tested for safety and efficacy before they are sold. The drug labels have to reveal potentially harmful side effects. In contrast, supplement manufacturers do not have to prove safety or efficacy, and there's little oversight of the manufacturing process. Canadian researchers tested popular supplements from 12 companies in 2013, and found that products from just two of the companies contained 100 percent of the supplement. The rest had been contaminated with other plants, had mislabeled ingredients, or contained mostly fillers like rice, soy or wheat. The New York Attorney General's office did similar DNA tests of herbal supplements in early 2015 and found that most didn't contain much — if any — of the actual herb on the label. 

2. Antioxidant supplements such as vitamins E, C and beta-carotene can help prevent heart disease and cancer. 

Myth. There's no evidence that antioxidants in pills prevent heart disease or cancer. Early lab studies suggested that increased levels of antioxidants might interfere with free-radical damage associated with the development of cancer. But most studies in people don't support that idea. In fact, there is evidence that the antioxidant beta-carotene increases the risk of lung cancer in smokers. 

3. Zinc can help you beat the common cold.

Maybe. A review of the research by the nonprofit Cochrane Collaboration found that zinc lozenges or syrup shortened the duration of colds by a day if the zinc was taken within 24 hours of the first cold symptom. However, zinc can also interfere with the absorption of copper and actually impair the immune system if regularly taken in high doses. Cochrane advises taking 75 mg/day of zinc on the first day of a cold "with caution." Stay away from zinc nasal sprays; they can cause permanent anosmia (loss of smell). And forget about Airborne and other formulas that contain a mishmash of vitamins and minerals that were once purported to cure colds. No evidence indicates these formulas work, and some contain relatively high levels of vitamin A, which can weaken bones. 

4. Probiotics can help prevent diarrhea when you take antibiotics.

Fact. Some evidence suggests that probiotics may prevent diarrhea caused by the use of antibiotics. But choose your product carefully. Many brands of yogurt do not contain the strains of Lactobacillus and Bifidobacterium that seem to help. (Yeasts, such as Saccharomyces, can also act as probiotics.) And even if the product does carry the Live & Active Culture seal from the National Yogurt Association, it only means that probiotics were present at the time of manufacture. There's no guarantee the probiotics are alive by the time you eat the yogurt. Although you don't need a prescription for probiotics, it's important to talk to your doctor first, and take the probiotic your doctor recommends. They are, after all, live microorganisms and may not be safe for people with compromised immune systems or those who are seriously ill.

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5. Calcium supplements can prevent bone fractures in older women. 

Probably a myth. It is true that calcium is necessary for our bodies to build bone, and calcium deficiency can lead to bone problems. And, research indicates that adequate calcium plays a small beneficial role in people age 50 and older. The best way to reap the benefits is to eat foods that naturally contain calcium, such as milk, yogurt, collard greens and canned salmon. But, many Americans fall short on getting enough through their diet — 1,200 mg for women over age 50 and 1,000 mg for other adults. If that’s the case, supplements are worthwhile.

6. Supplements don't offer the same health benefits as food.

Fact. Time and again, researchers have seen a health benefit in people who eat a particular food containing a nutrient of interest. They test the nutrient in the lab and see promise of a positive health effect. Then, the supplements industry isolates the nutrient and puts it into a pill to sell. Years later, clinical trials show little or no benefit to the nutrient in pill form. What's going on? Whole food contains a variety of essential nutrients that work together in complex ways to benefit our bodies. Individual nutrients in pills have, at most, a small effect on chronic diseases. At worst, they can harm you. For example, too much vitamin A has been linked to osteoporosis and an increased risk of hip fractures. Cancer patients are warned not to take antioxidant supplements such as beta-carotene and vitamins A, C and E, out of concern that they may interfere with treatment or cause the cancer to grown faster. The bottom line: Whole foods such as fruits, vegetables, whole grains, fish and milk offer a rich mix of micronutrients that give most of us all we need for optimal health. [The Truth About Herbal Supplements for Stress ]

There are often more questions about supplements than answers, and it's important (as with any questions you have about health) that you seek out trusted experts, question the claims you do hear, and remember that information is the best medicine. 

Read more from the UC Berkeley Wellness Letter: Supplement Claims: What's Allowed, 10 Ways to Spot Health Quackery, and Should You Listen to Dr. Oz?.

Follow all of the Expert Voices issues and debates — and become part of the discussion — on Facebook, Twitter and Google+. The views expressed are those of the author and do not necessarily reflect the views of the publisher. This version of the article was originally published on Live Science.