Background – There is little information about whether the effects of milk supplementation on bone turnover markers still persist, 3 years after supplements cease.
Objectives – To assay biochemical markers of bone turnover and also calcitropic hormones in blood, 3 years after the completion of a milk supplementation trial.
Design – A follow-up study of a two-year school milk intervention trial, in which 757 Beijing girls aged 10 years at baseline were assigned into Ca-fortified milk (Ca milk), Ca plus vitamin D-fortified milk (CaD milk) and control groups. Three years after the completion of intervention, fasting blood and urine samples were collected at the end of winter (March to April) from 504 girls. Using standard assay kits, the blood concentrations of osteocalcin (OC), bone alkaline phosphatase (BAP) and the urine deoxypyridinoline /creatinine (Dpd/Cr) ratio were used as bone biomarkers. Plasma calcium (PCa), parathyroid hormone (PTH) and insulin-like growth factor-I (IGF-I) were also measured.
Outcomes – Three years after milk supplement withdrawal, there were no significant differences in BAP, Dpd/Cr, PCa, PTH and IGF-I between groups after adjusting for baseline values, baseline pubertal stage and clustering by schools. However, the Ca milk group subjects had a significantly greater percentage increase in plasma OC concentration than controls over the 5 years from the pre-supplement baseline (21.5 ± 10.1%; P=0.04).
Conclusions – The effects of milk supplementation on biochemical markers of bone turnover and on calcitropic hormones were no longer present 3 years after the cessation of milk supplementation.
Funding – Danone-China, Nestle Foundation.