Folic acid is essential for DNA synthesis, and, along with vitamins B-6 and B-12, converts homocysteine to methionine. High homocysteine levels have been associated with diseases of the heart, as well as stroke, dementia and Alzheimer's. While a high intake of folic acid reduces homcysteine levels, research on its role in the prevention of these medical conditions is inconclusive. Moreover, the U.S. National Library of Medicine states that folic acid intake of more than twice the RDA over extended periods may increase the risk of heart attack and some cancers. The Harvard Medical School recommends high intake of folic acid for people who are pregnant or deficient in folic acid.
Recommended Intake of Folic Acid
Best known as the vitamin that prevents birth defects such as spina bifida and anencephaly, doctors generally prescribe folic acid to women before and during pregnancy. Need for folic acid is high during periods of growth because it plays an important role in cell division and DNA synthesis. While the recommended dietary allowance for adults is 400 mcg of folate per day, needs increase to 600 mcg during pregnancy and 500 mcg during lactation. Because alcohol interferes with absorption and metabolism of folate, the recommended intake for people who drink regularly is 600 mcg.
Upper Limit for Folic Acid Intake
Folic acid and vitamin B-12 deficiency share the symptoms of megaloblastic anemia, characterized by enlarged, immature red blood cells. A high intake of folic acid cures the anemia but allows the deficiency of vitamin B-12 to go on unnoticed, by masking other symptoms of vitamin B-12 deficiency. Prolonged deficiency of vitamin B-12 may cause irreversible nerve damage. For this reason, the maximum amount of folic acid intake from fortified foods and supplements has been set at 1,000 mcg.
Mega-Dose of Folic Acid
According to the U.S. National Library of Medicine, high doses of folic acid may cause abdominal cramps, diarrhea, sleep disorders, irritability, confusion, nausea, upset stomach, skin reactions, seizures and gas. Intake of 800 to 1,200 mcg over extended periods may also increase risk of heart attack and of some cancers. In a 2010 study reported in the "The Journal of the American Medical Association," researchers found that diabetic patients on a high dose of folic acid, vitamin B-6 and vitamin B-12 had an increased incidence of heart attacks and stroke, and a decrease in kidney function.
Food Sources
Depending on the source, this water-soluble vitamin is present in the diet in one of the two forms. In natural foods, this B complex vitamin is available in the form of folate. Fortified foods and supplements contain folic acid, which is the synthetic and more stable form of the vitamin. Some of the best sources of folates and folic acid are vegetables, fruits, beans, whole grains, fortified breakfast cereal, breads and processed foods. Unless recommended by a doctor, you should avoid taking mega doses of folic acid. Sufficient amounts can be obtained by eating a well-balanced diet.
References
- Harvard School of Public Health: The Nutrition Source: Three of the B Vitamins: Folate, Vitamin B-6, and Vitamin B-12
- National Institutes of Health: U.S. National Library of Medicine: Folic Acid; June 2011
- Harvard Medical School: The Ups and Downs of Folic Acid Fortification; March 2008
- "The Journal of the American Medical Association"; Effect of B-Vitamin Therapy on Progression of Diabetic Nephropathy; Andrew A. House et al.; April 2010
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