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Folic acid can overwhelm the human liver

August 24, 2009 | 12:00 pm

 A new study brings fresh evidence that it is indeed possible to have too much of a good thing.

Writing in today’s edition of the Proceedings of the National Academy of Sciences, researchers from the University of South Alabama find that most people who take folic acid supplements probably shouldn’t.

FolicFolic acid is a synthetic compound that is supposed to break down into folate, or vitamin B9, inside the body. Found naturally in foods like leafy green vegetables and legumes, folate is necessary to help the body produce new cells.

The U.S. Reference Daily Intake is 0.4 milligram for adults – slightly higher for women who are pregnant or nursing – and most everyone hits that target simply by eating fortified breads and cereals (and additional fortified foods are hitting the market all the time). Supplements are popular, but they often wind up boosting levels of unmetabolized folic acid in the bloodstream and in tissues. Recent studies have linked high levels of unmetabolized folic acid to decreased activity of natural killer cells in older women, and they may make it difficult to detect deficiencies in B12. Too much folic acid also appears to boost the progression of some types of cancer. (For more, see this L.A. Times story from May.)

The Alabama scientists figured out why it seems to be so easy for folic acid to build up in the body – human livers convert folic acid to folate 56 times slower than previously thought.

Earlier estimates were based on studies of rat livers, which were assumed to be very similar to their human counterparts. But when Steven Bailey and June Ayling got their hands on six fresh liver samples from surgical patients and organ donors, they found that assumption was way off base.

Their findings would seem to explain why clinical studies to test the ability of folic acid to reduce the risk of heart disease, stroke and Alzheimer’s disease have had disappointing results, the researchers wrote. The trials used doses as high as 5 milligrams per day, but most of that folic acid probably passed straight through the body.

-- Karen Kaplan

Photo: This plate contains way more folic acid than anyone should consume in one day. Credit: Carlos Chavez/Los Angeles Times