No heart benefits for folic acid supplements

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Use of folic acid supplements appears to lower blood levels of the amino acid homocysteinetheorized to be a risk factor for heart and blood vessel diseasebut does not appear to be linked to reduced rates of cardiovascular events, cancer or death over a five-year period, as per a meta-analysis of previously published studies in the October 11 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

"Elevated plasma total homocysteine [an amino acid created by the body, commonly as a byproduct of eating meat] has been suggested as a potentially modifiable risk factor for coronary heart disease, stroke and other occlusive vascular conditions," the authors write as background information in the article. High rates of cardiovascular disease in children with homocystinuriaa rare genetic condition causing extreme elevations in homocysteine levelsled scientists to hypothesize that moderate increases in blood homocysteine levels may increase cardiovascular disease risk in the general population.

Supplementation with B vitamins, and in particular folic acid, lowers blood homocysteine levels and reduces cardiovascular disease risk among individuals with homocystinuria. Several large clinical trials conducted in patients without the condition have been inconclusive. "Consequently, a collaboration between their researchers was established in 2004 to conduct a meta-analysis based on individual participant data from all large randomized trials of folic acidbased B-vitamin supplementation intended to lower plasma homocysteine levels for the prevention of cardiovascular disease," the authors write.

Robert Clarke, F.R.C.P., University of Oxford, England, and his colleagues in the B-Vitamin Treatment Trialists' Collaboration report the results of the meta-analysis of all eight trials completed by the end of 2009. Of a total of 37,485 participants, 18,723 were assigned to take folic acid in doses ranging from 0.8 milligrams per day to 40 milligrams per day. The other 18,762 took placebo or an equivalently small dose of folic acid. Trials continued for a median (midpoint) of five years.

Among the 37,485 participants, 9,326 had a major vascular event during the therapy period, 3,010 developed cancer and 5,125 died. Overall, there was a 25 percent reduction in homocysteine levels linked to active folic acid supplementation. However, those who took folic acid were no less likely to have a major heart or blood vessel event than those who took placebo (4,670 or 24.9 percent of first events occurred in those taking folic acid, compared with 4,656 or 24.8 percent in the placebo group).

In addition, there was no significant difference between folic acid and placebo groups in the number of patients experiencing major coronary events (2,019 or 11.4 percent vs. 1,971 or 11.1 percent); stroke (747 or 4.2 percent vs. 781 or 4.4 percent); new cases of cancer (1,541 or 8.7 percent vs. 1,469 or 8.2 percent) or death (2,578 or 13.8 percent vs. 2.547 or 13.6 percent).

"The doses of folic acid used in all the trials included in this meta-analysis exceeded those mandatory for near-maximal reduction in homocysteine levels," the authors write. "The randomized trials in the present meta-analysis found no evidence of benefit with therapy continued for more than five years. Eventhough some benefit might emerge with even longer therapy and follow-up, the trial results give no reason to expect this (especially because cardiovascular benefits tend to emerge within just a few years with other cardioprotective therapys, such as antihypertensives or statins)."

"One-third of adults in the United States and one-quarter of those in the United Kingdom report taking daily multivitamin supplements containing folic acid," they conclude. All doses in the trials were greater than those mandatory in the United States, where foods are fortified with folic acid to prevent neural tube birth defects. "Eventhough the lack of any other benefits is disappointing (albeit fairly definitive), the lack of any significant adverse effects on vascular events, cancer incidence, cancer mortality and overall mortality provides reassurance about the safety of population-wide folic acid fortification".


Posted by: Daniel    Source