Vitamins, minerals, and supplements, which are supposed to strengthen your bones, boost your memory, protect your heart, and help you stay healthy, are popular—more than 50 percent of U.S. adults take these widely sold over-the-counter products.
But evidence shows that excessive vitamin and supplement consumption is unnecessary, and many products could be a waste of money. What's more, some are potentially harmful:
- A 10-year study followed more than 14,000 men ages 50 and older who took 400 international units (IU) of vitamin E every other day and 500 mg of vitamin C daily. That’s much more than the recommended daily intake but less than the upper limit set by the Institute of Medicine of the National Academies. The vitamins didn’t reduce the risk of major cardiovascular events, and vitamin E was linked to an increased risk of hemorrhagic stroke, caused by a burst blood vessel.
- A study of more than 35,000 men, published last fall in the Journal of the American Medical Association, found that high-dose selenium had little effect on prostate-cancer risk, despite earlier research suggesting that selenium might help protect men. Worse still, the study found that supplemental vitamin E increased the risk of prostate cancer by 17 percent, though researchers couldn’t explain why.
- A large long-term study published last fall in the Archives of Internal Medicine tracked almost 39,000 postmenopausal women for as long as 22 years. It found that those who took multivitamins, vitamin B6, folic acid, iron, magnesium, zinc, or copper had a slightly higher risk of death than those who did not. The risk was especially pronounced for those who took iron.
Vitamin and supplement don'ts
The advice below will help you make smart decisions.
Don’t assume all supplements are safe
Surveys of consumers have shown that many think the U.S. Food and Drug Administration clears all supplements before they are sold. That’s not the case. The FDA doesn’t generally verify claims made by supplement manufacturers before products reach the market, and federal law doesn’t require dietary supplements to be tested for content, safety, or efficacy. One quality indicator is the USP-Verified mark, which means that products that carry it (including their raw ingredients) have met the U.S. Pharmacopeia’s high standards. Go to USP.org for a list of brands and products. (If you have kids, read our report on vitamins and supplements for children.)
A Consumer Reports investigation in 2010 found 12 supplements you should steer clear of: aconite, bitter orange, chaparral, colloidal silver, coltsfoot, comfrey, country mallow, germanium, greater celandine, kava, lobelia, and yohimbe. In addition, be aware that harmful ingredients have been found in many supplements, especially those that claim to boost weight loss, enhance your sex life, or increase muscle mass.
Don't rely on biased information from some retailers
Don’t substitute pills for vegetables
The marketing for Centrum’s new ProNutrients Fruit & Veggie pills says each one “harnesses the power equal to one serving of a blend of fruits and vegetables.” But it also states that the product “is not intended to replace your daily intake of fruit and vegetables.” No pill can replicate the benefits of produce. Researchers don’t know exactly why, but evidence shows that stripping nutrients from food reduces their effects. Bottom line: Rely on produce, not pills!
Don't assume you need a multi
Evidence shows they don’t boost the average person’s health, so if your doctor recommends taking one, ask why. A 2011 study of 182,000 people found that taking multivitamins didn’t cut the risk of death from cancer, cardiovascular disease, or other conditions; nor did they reduce the risk of getting cancer. To get the nutrients you need, eat them. Go for nutrient-packed legumes, nuts, low-fat dairy products, dark-green leafy vegetables, whole grains, citrus fruit, and berries.
Don’t take extra vitamin A
This vitamin is important for your vision and helps regulate cell division, build bone, and fight infections. But taking too much from supplements can weaken bones and lead to birth defects, liver damage, and disorders of the central nervous system. And there’s some evidence that it can impair vitamin D absorption, already a problem for many older adults. The Institute of Medicine recommends that healthy adults avoid vitamin A supplements. If you take a multi that contains vitamin A, make sure it doesn’t have more than 2,500 IU from preformed vitamin A, which is derived from animal sources (sometimes called vitamin A acetate or vitamin A palmitate on labels). In its plant-based precursor form, betacarotene, vitamin A is abundant in carrots, cantaloupes, sweet potatoes, and spinach. Deficiencies are rare in the U.S.
Don’t mix pills that can lead to bad reactions
Supplements can be dangerous when combined with prescription drugs. Vitamin C, for example, has been shown to reduce the potency of many chemotherapy drugs. The herb St. John’s wort can interfere with oral contraceptives, seizure medication, blood thinners, and antidepressants. And if you take the blood thinner warfarin (available under the brand name Coumadin and as a generic), you should avoid a long list of popular supplements, including ginkgo biloba, ginseng, saw palmetto, and St. John’s wort. So if you’re taking any medicine, talk with your doctor before you buy any supplements. And if you’re prescribed a medication, tell your doctor about any supplements you’re taking.
Taking megadoses of certain vitamins and supplements, unless under medical supervision, isn’t a very good idea. High doses of vitamin E taken over a long period have been linked to a small but increased risk of lung cancer. Very high levels of vitamin D can cause kidney and tissue damage, and too much calcium can lead to kidney stones. Fish oil may reduce the risk of stroke, particularly ischemic stroke, the most common kind, but too much may increase the risk of hemorrhagic stroke, the less common but more deadly kind. An overdose of iron can damage organ function, and if left untreated can lead to death.
One way to overdo it is to take a multi on top of individual vitamins and mineral pills and/or
nutrient-packed drinks. Our advice: Tally the amount of each nutrient you take and go over it with your doctor. You can look up nutrient amounts in products at the U.S. National Library of Medicine’s Dietary Supplement Label Database. Also, if your doctor says you need more of a specific nutrient, ask about the best way to get it. A single vitamin or mineral pill might be all you need.
Don't keep secrets from your doctor
Involve him or her in the decision-making process about which supplements you’re considering—or whether you should take them at all. Your doctor can diagnose deficiencies and help determine whether you need more of a certain nutrient.
Some doctors “prescribe” vitamin and mineral add-ons based on a patient’s age, diet, and individual health issues and risks. If your doctor isn’t well-versed about supplements, consider consulting a dietitian to work with him or her. (Find one at Eatright.org.) Another option: Consider consulting one of a growing number of integrative medicine physicians. To find one near you, use the practitioner finder created by the Arizona Center for Integrative Medicine.