Global DNA methylation changes in response to chronic consumption and withdrawal of low, moderate, and high folic acid doses

The effect of chronic folic acid supplementation (100, 400, 4000 μg/d) and withdrawal on global DNA methylation in reproductive age Chinese women (n=135; 45/treatment group) not currently exposed to folic acid was evaluated. DNA methylation was expressed as a percent of methylated cytosines (as measured by a novel LC‐MS/MS assay) at 0, 1, 3, 6 month of supplementation, and after a 3 month washout period. Mean (±SD) DNA methylation decreased by 13% (p < 0.001) between baseline (4.44 ± 0.18) and 1 mo (3.83 ± 0.42), but did not change further (p = 0.4) during intervention (3.84 ± 0.41 at 3 mo, 3.91 ± 0.74 at 6 mo). During the 3 month washout period, DNA methylation decreased a further 23% relative to baseline (to 3.44 ± 1.18; p < 0.0001), with ~18% of subjects exhibiting a >50% drop in methylation (maximum decrease = 94%). The response was dose independent. In conclusion, a moderate reduction in global DNA methylation was observed in response to folic acid supplementation relative to a larger drop in response to folic acid withdrawal. These data suggest that some subjects might be acutely sensitive to folic acid withdrawal. Supported by a collaborative CDC agreement and the GCRC Grant # MO1‐RR00082.