Plasma 25-hydroxyvitamin D responses of younger and older men to three weeks of supplementation with 1800 IU/day of vitamin D

Objective: The objective of this study was to compare changes in plasma 25-hydroxyvitamin D (25(OH)D) levels of younger and older men after three weeks of oral vitamin D supplementation. Methods: Nine younger men (22 to 28 years) and nine older men (65 to 73 years) with self-reported vitamin D intakes below 200 IU/d were enrolled in February and randomized to 1800 IU/d of ergocalciferol (vitamin D-2, n=11) or to a control group (n=7) and followed for three weeks. Blood was collected at baseline, and after one, two and three weeks for measurement of plasma concentrations of total 25(OH)D, 25(OH)D-2 and 25(OH)D-3. Results: in both the younger and older supplemented men, 25(OH)D-2 and total 25(OH)D concentrations increased significantly during the study, whereas values of these metabolites did not change in younger or older control subjects. No group showed significant changes in 25-hydroxyvitamin D-3. There was a significant interaction between age group and supplement group, suggesting that the effect of vitamin D, supplementation on changes in 25(OH)D-2 changes with age. The mean increase in 25(OH)D-2 was greater in the younger supplemented men than in the older supplemented men (37+/-9 nmol/L vs. 19.5 nmol/L, p=0.027), and this accounted for their significantly greater increase in total 25(OH)D. Conclusion: These data are consistent with an age-related decline in the absorption, transport or liver hydroxylation of orally-consumed vitamin D.