The Truth About Folic Acid: It May Be Both Boon and Bane

For two months in 1961, hematologist Victor Herbert ate only boiled chicken and applesauce. He thought that a deficiency of a vitamin called folate caused anemia, and he was right. His health deteriorated until he was bedridden, and only improved when he resumed eating vegetables.

Thanks in part to Herbert's self-experiment, today's doctors know that folate, or vitamin B9, is essential for everyone, and especially vital for pregnant women. Folate is found in fruits, dried beans, peas, nuts and leaves of green vegetables such as spinach (the word "folate" comes from the same Latin root as "foliage," which means leafy).

Folic acid, a synthetic folate, is used to enrich multivitamins and fortified grain products because it has a longer shelf life than natural folates.

A sort of molecular multipurpose tool, folate is necessary to make red blood cells, and it works with other vitamins to help the body use dietary proteins. DNA can't reproduce without it, which makes folate crucial to fetal development. A lack of folate in a woman's body immediately preceding or during pregnancy can cause her baby to develop neural tube defects, a category of severe developmental problems that includes spina bifida and anencephaly.

To help prevent neural tube defects, the U.S. government started requiring the addition of folic acid to refined grain products in 1998. Folic acid can now be found in breakfast cereals, egg noodles, rice, bread and other products. Although the enrichment program was an unqualified success, leading to a 19 percent decline in neural tube defects, studies have since both reaffirmed and called into question the value of added dietary folate.

Research has suggested that supplemental folate may help fight conditions as far ranging as Alzheimer's, heart disease and cancer. However, extremely high levels of folate may promote cancer. And one group of researchers recently suggested that the body can't transform synthetic folic acid into biologically useful molecules as efficiently as previously thought.

One widely acknowledged concern is that the overconsumption of folate may mask a vitamin B12 deficiency. Normally, a lack of vitamin B12 leads first to anemia, which doctors can easily diagnose, and then neurological damage if the deficiency goes uncorrected. Excess folate in the diet can prevent anemia, making neurological symptoms the first indication of B12 deficiency, at which point permanent damage may already be done.

Older adults, people with gastrointestinal disorders or who have had gastrointestinal surgery, and vegetarians, especially those who are pregnant, are at highest risk for vitamin B12 deficiency.

Adults should consume 400 micrograms of folate daily, according to the 2010 U.S. Department of Agriculture dietary guidelines. A typical multivitamin contains 400 micrograms of folic acid, and a typical slice of enriched whole wheat bread contains 16 micrograms.

Women who might become pregnant should consume 400 micrograms of synthetic folic acid per day, in addition to the folate acquired in a varied diet, and pregnant women should consume a total of 600 micrograms of folate per day.

The National Institutes of Health recommends a maximum daily intake of 1,000 micrograms of folic acid from fortified foods and supplements.

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Source: National Institutes of Health Dietary Supplement Fact Sheet: Vitamin B9.