Milk intake and bone mineral acquisition in adolescent girls: randomised, controlled intervention trial

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Abstract
Objectives: To investigate the effect of milk supplementation on total body bone mineral acquisition in adolescent girls. Design: 18 month, open randomised intervention trial. Subjects: 82 white girls aged 12.2 (SD 0.3) years, recruited from four secondary schools in Sheffield. Intervention: 568 ml (one pint) of whole or reduced fat milk per day for 18 months. Main outcome measures: Total body bone mineral content and bone mineral density measured by dual energy x ray absorptiometry. Outcome measures to evaluate mechanism included biochemical markers of bone turnover (osteocalcin, bone alkaline phosphatase, deoxypyridinoline, N-telopeptide of type I collagen), and hormones important to skeletal growth (parathyroid hormone, oestradiol, insulin-like growth factor I). Results: 80 subjects completed the trial. Daily milk intake at baseline averaged 150 ml in both groups. The intervention group consumed, on average, an additional 300 ml a day throughout the trial. Compared with the control group, the intervention group had greater increases of bone mineral density (9.6% v 8.5 %, P=0.017; repeated measures analysis of variance) and bone mineral content (27.0% v 24.1 %, P=0.009). No significant differences in increments in height, weight, lean body mass, and fat mass were observed between the groups. Bone turnover was not affected by milk supplementation. Serum concentrations of insulin-like growth factor I increased in the milk group compared with the control group (35% v 25 %, P=0.02). Conclusion: Increased milk consumption significantly enhances bone mineral acquisition in adolescent girls and could favourably modify attainment of peak bone mass. Osteoporosis is a major public health problem; 40% of women will sustain an osteoporotic fracture Maximising peak bone mass at skeletal maturity may be one of the most important protective measures against fracture in later life Adolescence is a critical time for bone mineral acquisition An increase in milk consumption among adolescent girls resulted in significant gains in bone mineral over an 18 month period This simple intervention indicates that increased milk consumption may be associated with higher peak bone mass