Serum 25(OH)D concentrations (ng/ml) were significantly ( P < 0.001, treatment, time interaction) modified following supplementation. Although there were no significant differences in the placebo or 200 IU groups, serum 25(OH)D concentrations increased after 7-d (1 P < 0.001 vs. Pre) and continued to increase thereafter (2P < 0.001 vs. Pre and 7-d; 3P < 0.001 vs. Pre, 7-d, 14-d and 21-d) in the 4000 IU group. Serum 25(OH)D concentration differences between groups at Pre were not significant. However, serum 25(OH)D concentrations were significantly (*P < 0.05 vs. placebo) increased in the 200 and 4000 IU groups compared to those in the placebo group after supplementation. By 28-d, serum 25(OH)D concentrations were significantly (#P < 0.05 vs. 200 IU) increased in the 4000 IU compared to those in the 200 IU group. Data presented as mean (SD).