After stratified randomization by mini mental state examination scores, supplement group subjects take 1 mg of methylcobalamin and 5 mg of folic acid daily, while placebo group subjects take placebo capsules. The primary outcome is Mattis dementia rating scale. The secondary outcomes are mini mental state examination, neuropsychiatric inventory, and Cornell scale for depression in dementia. These measurements will be performed at baseline and every six months for 24 months. Fasting plasma homocysteine concentrations are measured at baseline and 18-month follow-up.