Among the 37,485 participants, 9,326 had a major vascular event during the treatment period, 3,010 developed cancer and 5,125 died. Overall, there was a 25 percent reduction in homocysteine levels associated with 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 required for near-maximal reduction in homocysteine levels," the authors write. "The randomized trials in the present meta-analysis found no evidence of benefit with treatment continued for more than five years. Although some benefit might emerge with even longer treatment and follow-up, the trial results give no reason to expect this (particularly because cardiovascular benefits tend to emerge within just a few years with other cardioprotective treatments, 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 required in the United States, where foods are fortified with folic acid to prevent ne
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