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A dose-finding trial of the effect of long-term folic acid intervention: implications for food fortification policy

Tighe, Paula, Ward, Mary, McNulty, Helene, Finnegan, Owen, Dunne, Adrian, Strain, JJ, Molloy, Anne M., Duffy, Maresa, Pentieva, Kristina, Scott, John M.
American journal of clinical nutrition 2011 v.93 no.1 pp. 11-18
folic acid, nutritional intervention, long term effects, dosage, dose response, food fortification, fortified foods, adverse effects, nutrient excess, homocysteine, blood chemistry, adults, temporal variation
BACKGROUND: The lowest dose of folic acid required to achieve effective reductions in homocysteine is controversial but important for food fortification policy given recent concerns about the potential adverse effects of overexposure to this vitamin. OBJECTIVE: We compared the effectiveness of 0.2 mg folic acid/d with that of 0.4 and 0.8 mg/d at lowering homocysteine concentrations over a 6-mo period. DESIGN: A randomized dose-finding trial with folic acid was conducted. Of 203 participants screened, 101 patients with ischemic heart disease and 71 healthy volunteers completed the study. Participants were randomly assigned to receive placebo or folic acid at doses of 0.2, 0.4, or 0.8 mg/d for 26 wk; subsamples of patients with ischemic heart disease were also examined at 6 or 12 wk. RESULTS: Participants with higher baseline homocysteine concentrations had the greatest reductions in homocysteine in response to folic acid doses of 0.2 mg (-20.6%), 0.4 mg (-20.7%), and 0.8 mg (-27.8%); in those with lower baseline homocysteine concentrations, the responses were -8.2%, -8.9%, and -8.3%, respectively. No significant differences in homocysteine responses to the different doses were observed. In the patient group sampled at intervals during the intervention, the maximal homocysteine response appeared to be achieved by 6 wk in the 0.8-mg/d group and by 12 wk in the 0.4-mg/d group. However, the homocysteine response was suboptimal in the 0.2-mg/d group at both 6 and 12 wk compared with that at 26 wk. CONCLUSIONS: A folic acid dose as low as 0.2 mg/d can, if administered for 6 mo, effectively lower homocysteine concentrations. Higher doses may not be necessary because they result in no further significant lowering, whereas doses even lower than 0.2 mg/d may be effective in the longer term. Previous trials probably overestimated the folic acid dose required because of a treatment duration that was too short. This trial was registered at as ISRCTN45296887.