The purpose of this study is to determine whether folic acid supplementation are effective on arsenic lowering in a chronic, low-level arsenic exposed population.

Outcome measure:

Changes of arsenic metabolites at baseline and week 8

Methods High-performance liquid chromatography (HPLC)

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;