Intervention with 800 IU/day of vitamin D in patients with AD may ameliorate the cognitive function and reduce Aβ-associated biomarkers. The results of the intervention group showed significant amelioration of plasma Aβ42, APP, BACE1, APP mRNA, BACE1 mRNA (p < 0.001) levels and information, arithmetic, digit span, vocabulary, block design and picture arrange scores (p < 0.05) unlike the control group. The gene discussed is BACE1; the disease is Alzheimer disease.