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Most supplements are useless. There’s one big exception when it comes to women.

The US Preventive Services Task Force is advising all women of childbearing age to take folic acid.

Supplements that aren't prescribed by a doctor are mostly useless and sometimes dangerous. Not folic acid.
ZenShui/Frederic Cirou/Getty

There’s one really, really helpful supplement that women of childbearing age should consider taking: folic acid. Unfortunately, less than half of us bother to use it despite years of public information campaigns.

In numerous systematic reviews, researchers have found dramatic reductions in terrible birth defects when women take folic acid, a type of B vitamin, just before and during the first few months of pregnancy.

That’s why the US Preventive Services Task Force, an independent panel of experts who make evidence-based health recommendations, today reaffirmed its position that all women who are planning on becoming pregnant, or who are capable of pregnancy, should take a daily supplement that includes 0.4 to 0.8 milligrams of folic acid.

Their advice may sound like it overreaches, particularly for women who aren’t trying to get pregnant. But it’s actually pretty reasonable: About half of pregnancies in the US are unplanned, and the stakes of folate deficiency among babies are very high. That makes folic acid one of the (rare) exceptions where there’s really, really strong evidence that a supplement is a good idea. (As we’ve reported, supplements that aren't prescribed by a doctor are mostly useless and sometimes dangerous.)

The potential effects of folate deficiency in pregnancy are terrible

In 1991, researchers discovered that folic acid supplementation can prevent neural tube defects, which are problems with the development of the brain, skull, and spine. These issues arise when the neural tube — a key embryonic structure — does not close properly. The two most common neural tube defects are anencephaly, where the baby is born without parts of the brain and skull, and spina bifida, in which the spinal cord and backbone don’t develop properly. Babies born with anencephaly usually die soon after birth, and spina bifida can lead to lifelong disabilities.

Since this discovery, public health officials around the world have waged information campaigns encouraging women to use the supplement, yet uptake in the United States remains low. Still, only 25 percent and 40 percent use the supplement (estimates vary). Among the most common reasons women cite for not taking folic acid before giving birth are that they didn’t plan their pregnancy, or they weren’t aware they should take it.

The neural tube defects folate prevents are still among the most common birth abnormalities, according to the Centers for Disease Control and Prevention. Anencephaly and spina bifida happened in 6.5 of every 10,000 live births between 2009 to 2011.

The good news is that there’s a simple way to reduce the chances of these awful effects: more folate supplementation.

The task force grades the quality of evidence for its various health recommendations, and in this case, it gave folic acid before and during early pregnancy the top score (an A), suggesting that there’s a great deal of certainty about its benefits.

It also looked at new evidence on the potential harms of folate supplementation, released since its last review in 2009. Some newer studies have associated folate supplementation with respiratory illness in children, and with having twins — but the task force concluded that these risks were “no greater than small” while the benefits were overwhelming.

The best time to start taking the supplement is before pregnancy

The best time to start taking the supplement is at least one month before conception through to the first two or three months of pregnancy, according to the task force. For women who aren’t planning a pregnancy but could become pregnant, the group suggests using the supplement anyway, since there are no major side effects or proven harms but a great deal of potential benefit.

Women (and men) can get folic acid from their diets — mainly in leafy green vegetables, citrus fruits, and beans. And since 1996, the government has been fortifying cereal grains with folate so that it makes its way into our breads, pastas, and cereals. Some research has suggested that food fortification may have reduced the benefit women get from folic acid supplements, but in its review of the evidence, the task force found those studies were mostly flawed and too small to deliver strong conclusions.

James Mills, a National Institutes of Health researcher focused on pregnancy and birth defects, also warned that even with food fortification, many women still don’t get enough folate. “For example, a women who does not eat enriched cereal grain early in pregnancy or who is on a diet that eliminates those products may still be at risk [of a pregnancy with neural tube defects],” he told Vox. In a JAMA editorial that accompanied the new task force advice, Mills noted that women on low-carb and gluten-free diets may be particularly susceptible to folic acid deficiency.

Since there are no symptoms that you’re not getting enough folate, a supplement — in this particular case — is a very good idea.

For more on how to buy safe supplements, read our guide.

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