The “Three B’s”
Just as the antioxidants were going from boom to bust, three more white knights burst onto the scene. The putative “heroes” were three B vitamins: B6 (pyridoxine), folate (also known as folic acid in its synthetic form), and B12 (cobalamin). The “villain” was homocysteine, an amino acid that’s present in everyone’s blood. Study after study linked high levels of homocysteine to a high risk of heart disease, and study after study showed that folic acid, alone or with B6 and B12, could reduce homocysteine levels.
Based on solid research, there was reason to hope that B vitamins, even in the amounts found in ordinary multivitamins, might reduce the risk of heart disease and stroke. But in the past few years, a series of randomized clinical trials has dashed these hopes. Except in people who have inherited a metabolic glitch that sends homocysteine levels sky-high, B vitamin supplements do not protect the heart or brain. It’s another major disappointment for supplements. Still, two of these B vitamins deserve an additional look.
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 pregnant women. It’s a rare success story for supplementary vitamins, but it may have an unintended negative consequence. Although normal amounts of folic acid appear to protect cells from malignant transformation, high amounts may fuel the growth of rapidly dividing tumor cells. And some recent studies suggest that even modest doses of supplementary folic acid, when added to the folic acid in fortified food and the natural folate in food, may increase the risk of colon cancer, prostate cancer, and breast cancer. Other studies find neither risk nor benefit; in any case, it’s not a worry for women who just take supplements that contain folic acid during pregnancy, and it’s no reason to shun healthful foods containing folate. But it does provide a cautionary note about the most popular of all supplements, the multivitamin.
Multivitamins. Despite their iconic status, there is no evidence that multivitamins enhance health and well-being or prevent illness. In fact, both the authoritative U.S. Preventive Services Task Force and a 2006 National Institutes of Health State-of-the-Science Conference concluded that multivitamins do not offer protection against heart disease or cancer.
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. In addition, multivitamins appeal to many scientists the way prayer appeals to many agnostics: “just in case.” But for multivitamins to have merit as a nutritional insurance policy, they must at least be safe. Are they?
We don’t know for sure. A 2007 study raised the possibility that men who take more than seven multivitamins a week face an increased risk of prostate cancer, particularly if they take other supplements as well. In addition, a 2011 study linked various supplements with an increased mortality rate in women. And the research about large amounts of folate adds to the concern.
A typical multivitamin provides just 400 mcg of folic acid, only 40% of the dose that has been shown to promote the growth of precancerous adenomas in the colon. But now that folic acid is added to so many fortified grains, it’s easy to see how a healthy diet high in whole grains and folate-rich vegetables and legumes could easily combine with a multivitamin to boost a person’s daily folate intake to 1,000 mcg (1 milligram) or even more.
Despite these worries, there is still no proof that a daily multivitamin is harmful. At the same time, though, there is no evidence that it is helpful. If it won’t help, even a slight chance of harm argues against taking a multivitamin. After all, one of the first principles of medicine is primum non nocere: first, do no harm.