BACKGROUND Increased plasma homocysteine is associated with coronary artery disease, peripheral vascular disease and venous thrombosis. Folic acid is the most effective therapy for reducing homocysteine levels. The lowest effective supplement of folic acid is not known, particularly for the elderly who have the highest prevalence of these conditions.    AIM To explore the effects of daily supplements of 0, 50, 100, 200, 400 and 600 microg folic acid on plasma homocysteine in an elderly population.   
 DESIGN Randomized double-blind placebo-controlled trial.   
 METHODS Participants (n=368) aged 65-75 years were randomly allocated to receive one of the treatments for 6 weeks. Plasma homocysteine was recorded after 3 weeks and 6 weeks of supplementation.   
 RESULTS Only the 400 microg and 600 microg groups had significantly lower homocysteine levels compared to placebo (p=0.038 and p<0.001, respectively). Using multiple linear regression and each individual's total folic acid intake (diet plus supplement), a total daily folic acid intake of 926 microg per day would be required to ensure that 95% of the elderly population would be without cardiovascular risk from folate deficiency.    DISCUSSION A daily folic acid intake of 926 microg is unlikely to be achieved by diet alone. Individual supplementation or fortification of food with folic acid will be required to reach this target.
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