Objective:To assess the effects of a 12-month vitamin D 3 intervention on cognitive function and blood inflammatory cytokines in subjects with Alzheimer's disease(AD). Methods:Two hundred and ten AD patients were randomly divided into the intervention and control groups, with 105 patients in each group.The intervention group received vitamin D 3 800 U/day and the control group received a placebo for 12 months.Repeated-measures analysis of variance was used to evaluate the effects of vitamin D and placebo on cognitive performance and blood inflammatory cytokines at baseline, month 6 and month 12. Results:During the follow-up, serum 25(OH)D 3( F=712.086, P<0.001)and 1, 25(OH) 2D 3( F=372.038, P<0.001)concentrations in the intervention group were significantly higher than those in the control group.Changes in FSIQ, VIQ and PIQ between the groups, between different time points and with interaction between the variables taken into account were statistically significant(all P<0.001). Compared with the control group, interleukin-6(IL-6)( F=341.344, P<0.001)and tumor necrosis factor-α(TNF-α)( F=9.580, P<0.001)levels in the intervention group were significantly decreased, and the ratio of Aβ40 to Aβ42 was increased( F=4.617, P=0.010). There were interaction effects between group and time.Except for intervention effects, the baseline concentration of 25(OH)D 3 was positively correlated with scores of FSIQ( β=0.016, P=0.031)and VIQ( β=0.017, P=0.031). Conclusions:Daily oral vitamin D 3 supplementation(800 U/day)for 12 months may improve cognitive function and change inflammatory cytokines in elderly patients with AD.