Dietary supplements are wildly popular. About half the adult population take at least one supplement. It's easy to understand why supplements are such big sellers. The public has a legitimate desire for good health, and the supplement industry has a strong desire for good sales.
Medications are regulated by the FDA. Before a prescription or over-the-counter drug can be sold in the United States, the manufacturer must submit data supporting its safety and efficacy, and after the medication is approved, the FDA continues to monitor adverse reactions. Even with all these safeguards, problems still occur, prompting the FDA to withdraw many medications and to require strong warning labels on others.
The Dietary Supplement Health and Education Act restricts the FDA's ability to regulate products marketed as "dietary supplements," even though most people buy them for health, not nutrition. Manufacturers can sell these products without submitting evidence of their purity, potency, safety, or efficacy.
For most claims made on product labels, the law does not require evidence that the claim is accurate or truthful. In fact, the FDA's first opportunity to weigh in comes only after a product is marketed, when it can take action against products that are adulterated, misbranded, or likely to produce injury or illness. Since nearly all supplements are used without medical supervision or monitoring, most of the estimated 50,000 adverse reactions that occur in the United States each year go unreported.
How do we really know?
If a supplement's label or ads won't give you reliable information, how can you find out if a supplement can help — or, for that matter, hurt? Although it's a slow process, careful, objective medical studies provide the guidance that counts.
In most cases, scientific investigations of supplements start with simple observational studies, in which researchers compare the health status of folks who take a particular supplement with the health of people who don't take the supplement. It's an important effort, but the results don't always hold up. So the next step is to conduct randomized clinical trials, in which volunteers are assigned by lot to take either the supplement or an identical-looking placebo ("dummy pill") while researchers track their health. In the best studies, neither the volunteers nor the researchers know who is getting the real thing until the code is broken at the end of the trial.
What do we know?
Everyone wants to know if supplements can help. It's a good question. Here's where we stand today — but you should keep an eye out for new results, since recommendations will change as scientific studies trickle in. Unfortunately, in most cases, the studies have failed to confirm our hopes, though there are exceptions.
Many people take supplements in the belief that they will preserve health or ward off illness; many others use supplements in an attempt to treat specific conditions that have already developed. We'll have a look at popular supplements in both categories, starting with preventive supplements used principally by healthy people.
Supplements for prevention
Vitamin D. To get vitamin D the old-fashioned way, by producing it in the skin, we need lots of sunshine. But as work has shifted from the farm to the office and as we've learned to use sunscreens to reduce the risk of skin cancer and wrinkles, many people lack sufficient amounts of the "sunshine vitamin." Older adults, patients with chronic illnesses, and people of color are at particular risk.
Vitamin D is needed to absorb calcium from the intestines; that's why vitamin D is so important for healthy bones. Current guidelines call for 600 IU (international units) a day below age 71 and 800 IU a day thereafter. But many experts recommend 800 to 1,000 IU a day for most adults; daily doses up to 4,000 IU are considered safe, but more can be toxic.
It's very hard to get the vitamin D you need from your diet; oily fish and fortified dairy products are the only important sources. So supplements do make good sense for most adults. The form known as vitamin D3 is usually recommended, but D2 is also effective; for best results, take your vitamin D along with a meal that has some fat. If you want to be sure you need this supplement, ask for a blood test; levels of at least 30 nanograms per milliliter are considered best.
Antioxidants. Vitamin E, vitamin A, beta carotene, and vitamin C were the favorites of the 1980s and early '90s. But many careful randomized clinical trials have not shown any benefit against heart disease, cancer, or other illnesses. And that's not the worst of it. In fact, even moderately high doses of vitamin A increase the risk of hip fractures, and high levels of vitamin A have been linked to an increased risk of prostate cancer; beta carotene increases lung cancer risk in smokers; and vitamin E increases the risk of prostate cancer and has been linked to an increase in respiratory infections, heart failure, and the overall death rate.
Do not take antioxidant supplements. One exception: people with moderate or advanced age-related macular degeneration (AMD) benefit from special antioxidant supplements that also contain zinc. Unfortunately, though, this preparation does nothing to prevent AMD in people who have healthy eyes.
The B vitamins
Vitamin B12 is found only in animal-based foods, so strict vegetarians may need supplements. In addition, many older people don't make enough of the stomach acid that's needed to liberate B12 from animal products so it can be absorbed. But B12 is also added to fortified grain products and other foods, and this synthetic B12 is easy to absorb even without stomach acid. That means a single bowl of cereal can provide your RDA of 2.4 micrograms (mcg) a day. Still, if your fortified grain consumption is erratic, a B12 supplement is reasonable.
Folate is more complex. The vitamin is essential for the production of red blood cells, and it has an important role in DNA production and in repairing defects in the genetic code. Although folate is present in a variety of leafy green vegetables, fruits, legumes, and meats, until the late 1990s, many Americans didn't get their RDA of 400 mcg from foods — and folate deficiencies during pregnancy sharply increase the risk of devastating birth defects. That's why the U.S. and Canadian governments issued regulations mandating folic acid fortification of all grain products (including cereal, bread, flour, pasta, and rice) from 1998 onward.
Folate fortification has eased the birth defect problem, but obstetricians still recommend supplements for women who are trying to conceive or who are already pregnant.
Multivitamins. Despite their iconic status, there is no evidence that multivitamins enhance health and well-being or prevent illness.
Without disputing these conclusions, many doctors have continued recommending (and taking) multivitamins. One rationale is that they are a convenient and inexpensive way to get vitamin D — but most preparations provide just 400 IU, much less than the 800 to 1,000 IU currently in favor.
Fish oil. For years, doctors have known that people who eat fish regularly enjoy some protection against heart disease and stroke. For people with cardiovascular disease who don’t eat fish regularly, taking a fish oil supplement is reasonable. But check with your doctor first. People who eat fish at least twice a week are not likely to benefit from extra fish oil.
If you decide to take fish oil, don't choose fish liver oil, which has too much vitamin A.
Fiber. Most people think of fiber supplements as a treatment for constipation. But a high intake of fiber has many potential benefits for several health conditions, ranging from heart disease and obesity to hernias, varicose veins, and diverticulitis. The National Academy of Medicine recommends 38 grams of fiber a day for men younger than 50, 30 grams a day for older men, 25 grams a day for women younger than 50, and 21 grams a day for women over 50. Whole grains, fruits, vegetables, nuts, and seeds are the best sources of fiber, but many people need supplements to meet these goals. If you need supplementary fiber, consider psyllium, which has the added benefit of lowering cholesterol levels.
Selenium. Few men had heard of this mineral until 1996, when American researchers reported that it appeared to reduce the risk of prostate cancer. Subsequent reports were mixed, raising doubts. Then in 2009, a 35,553-man multinational trial of selenium and vitamin E, alone or in combination, reported that neither selenium nor vitamin E had any benefit against prostate cancer. Selenium also appears to increase the risk of diabetes, and earlier studies dashed preliminary hopes that the supplement might protect against heart attacks. Selenium is not for you.
Supplements for prevention?
It's a disappointing scorecard. Most people stand to benefit from vitamin D, many from fiber, and some from fish oil. And sorry to say, popular supplements used to treat medical problems fare no better.
It's often hard to balance sober scientific judgments against simple, forceful claims for health in a pill. If you are considering taking a supplement, here are a few cautions:
- Beware of extravagant claims; if it sounds too good to be true, it is usually not true.
- Beware of testimonials and endorsements, especially from celebrities. Even the most sincere, well-meaning success stories offered by friends and relatives without financial incentives can't establish a product's safety or efficacy.
- Beware of the idea that if a little is good, more is better. Although vitamin A is essential for health, for example, doses that exceed the RDA (3,000 IU a day for men, 2,330 IU for women) increase the risk of fractures. And as noted above, a high intake of folic acid may increase the risk of certain tumors.
- Beware of meaningless terms. The list includes all-natural, antioxidant-rich, clinically proven, anti-aging, and other vague but seductive claims that a product will promote heart health, prostate health, sexual prowess, energy, weight loss, fat loss, muscle power, and the like.
- Beware of interactions between supplements and medications. A survey of over 3,000 people ages 57 through 85 found that 49% used at least one supplement, 81% used at least one prescription medication, and 37% of men over 74 used five or more prescription drugs. Always tell your doctors and pharmacists about any supplements you take and ask specifically about potential interactions with your prescription and over-the-counter medications.
- Beware of adulterated products. The FDA has withdrawn over 140 products that were laced with undisclosed pharmaceutical ingredients. Products touted for sexual performance, weight loss, and athletic performance are the most likely to be contaminated with medications.
- Beware of products that contain less — or more — than they claim. Since you won't have the protection of FDA oversight, it's hard for you to know what you're actually getting. In general, products that are voluntarily submitted for approval by private organizations like the United States Pharmacopeia (USP) or NSF International are your best bet.
Supplements, not substitutes
Until (or unless) better oversight is available, supplements are likely to remain the Wild West of American health. At present, only a few are likely to help, some may do more harm than good, and most will be little more than expensive disappointments. But false hopes can be toxic in their own right if they keep you from taking good care of yourself or getting the medical care you need. So even if you take supplements, be sure to eat well, exercise regularly, and work with your doctor to keep your cholesterol, blood pressure, and blood sugar in good control. And while you're seeing your doctor for check-ups, screening tests, and treatments, be sure to tell him about all your supplements. Many people are reluctant to tell physicians that they use alternative or complementary therapies, but full disclosure is important for health, particularly since supplements can have adverse interactions with medications.
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