11 avril 2012 3 11 /04 /avril /2012 07:32
Does folic acid -B9- improve immunity? About half of all Americans routinely take dietary supplements, the most common being multivitamin and multimineral supplements. Q. What do you know about taking extra folic acid to boost the immune system? A. Folic acid is the synthetic form of folate, a B vitamin that occurs naturally in some foods, including vegetables, fruits, and dried beans and peas—and is essential for health. Folate is vital for the production and maintenance of our bodies’ cells, especially during rapid periods of growth, such as pregnancy and infancy. It’s needed to make DNA and RNA, the genetic material that dictates cell functions, and it helps prevent changes to DNA that may lead to cancer. Since folate helps make and repair DNA, it makes theoretical sense that a deficiency of the vitamin could hamper immunity. In some animal experiments, severe folate deficiency has been found to impair immunity, but this hasn’t yet been shown in human studies, and even in animals, the health impact remains unclear. With regard to taking higher-than-recommended doses of folate or folic acid to prevent disease or improve overall health, the evidence from clinical trials is conflicting. For most healthy adults, the Recommended Dietary Allowance (RDA) of folate from both natural and synthetic sources (fortified foods and vitamin supplements) is 400 micrograms (mcg) a day. Pregnant women should take more—600 mcg a day—to reduce the risk of neural tube defects such as spina bifida in their babies. Others who may need more than the RDA include people with intestinal disorders that interfere with absorption of nutrients; people who take certain medications; and alcoholics, because alcohol reduces the absorption of folate and promotes its excretion through the kidneys. The Tolerable Upper Intake Level for folic acid from supplements or fortified foods is 1,000 mcg a day. Folic acid is water-soluble and any excess is excreted in the urine, so the risk of toxicity is small even if you exceed that limit. However, experts are uncertain about the long-term health effects of excess folic acid supplementation. Naturally occurring folate from foods is not associated with any health risk, so get as much of your daily requirement as you can from a healthy diet. If that’s not possible, take a multivitamin that contains 400 mcg of folic acid. — Celeste Robb-Nicholson, M.D.