Folic acid is another one of the B vitamins, referred to sometimes as folate (its related anion form), or simply as vitamin B9. The most notable role folate and folic acid play in bone health is in the detoxification of homocysteine, an amino acid linked with inflammation and increased fractures.

Anywhere from 5–50% of any given population (varying by geographic region and ethnicity) may have genetic variants that impact their ability to optimally metabolize folate and, thus, their ability to prevent homocysteine build-up, detoxify adequately, and keep inflammation at bay.

Homocysteine is a compound produced as a by-product of the metabolism of the amino acid methionine. Normally, homocysteine gets recycled as another substance or eliminated, but excess blood levels can accumulate as a result of genetic or nutritional factors. Excess homocysteine promotes both osteoporosis and atherosclerosis. The proper processing of homocysteine requires folic acid. Researchers suggest that around the time of menopause, women experience a reduced capacity to process homocysteine appropriately. It is not known whether this is a universal trait or one found only in more developed countries. Supplementing with folic acid has been found to improve this homocysteine processing problem.

Deficiency of folic acid is an extremely common problem in many parts of the world where diets of refined foods predominate. The average US intake is only about half the RDA. Women taking oral contraceptives or estrogen replacement, as well as users of alcohol and long-term users of anticonvulsant medications, are at special risk for drug-induced folic acid deficiency.

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