Effects of Folic Acid Supplementation on Arsenic Lowering

Inclusion Criteria: * Men or women more than 18 years of age and chronically exposed to arsenic (arsenic concentration of the drinking water \>10ug/L); * Population who had no folic acid supplementation in the 2 weeks before the study; * Women of childbearing age agreed to use a reliable contraception method during the study; * Everyone volunteered to participate and signed informed consent. Exclusion Criteria: * Pregnant or breast-feeding women; * Allergic to folic acid; * Having clearly defined allergic history; * Reported long-term use of folic acid and other vitamins B; * Having obvious signs or laboratory abnormalities which could affect the efficacy of folic acid; * Unsuitable to participate in the study based on the judgment of the investigators; * Not agree to cancel the medications which may affect serum folate concentration during the study period; * Subjects who plan to become pregnant during the study or move out of the area within the study period;