Vitamin D supplementation suppresses age-induced bone turnover in older women who are vitamin D deficient

There is a lack of evidence that improving vitamin D status, without changing calcium intake, has a positive effect on bone turnover as indicated by bone marker changes. The objective was to measure the effect of vitamin D supplementation, in vitamin D deficient women (25(OH)D concentration <50 nmol/L), on osteocalcin (OC) and C-telopeptide (CTX). The study design was a randomised controlled intervention administering 4000 IU vitamin D3 or placebo daily for 6 months to South Asian women, aged >20 years. Subjects were stratified by age and menopausal status. Median (25th, 75th percentile) serum 25(OH)D increased significantly from 21 (11, 40) to 75 (55, 84) nmol/L with supplementation. In women >49 years or postmenopausal (n = 26), who were not supplemented (n = 13), CTX and OC levels increased (P = 0.001, P = 0.004 respectively), indicating an increased rate of bone turnover. With supplementation CTX decreased (P = 0.012) and there was no significant change in OC. In women who were under 49 years and premenopausal (n = 55; 29 supplemented), there was no significant response to supplementation in either CTX or OC. We conclude that correcting vitamin D deficiency in older women suppresses the age-induced increase in bone turnover and reduces bone resorption which would normally be exacerbated in conditions of low serum 25(OH)D.