ORIGINAL ARTICLE High intake of milk, but not meat, decreases bone turnover in prepubertal boys after 7 days AZ Budek, C Hoppe, KF Michaelsen and C Mølgaard Department of Human Nutrition, Faculty of Life Science, University of Copenhagen, Frederiksberg, Denmark Objective: To compare the short-term effect of a high milk and a high meat intake, identical in protein amount, on bone turnover during prepuberty. Setting: A University Department. Design and Subjects: From 28, randomly recruited, 8-year-old boys, first 14 were assigned to the milk group and next 14 to the meat group. In each group, 12 boys finished the dietary intervention. Intervention: Milk (1.5 l/day) and meat (250 g/d), both containing B53 g of protein, were given together with the habitual diet for 7 days. At baseline and day7, serum osteocalcin (s-OC), bone-specific alkaline phosphatase (s-BAP) and C-terminal telopeptides of type I collagen (s-CTX) were measured (immunoassay) and dietary intake was estimated (a 3-day weighted food record). Results: Baseline s-OC, s-BAP and s-CTX were not significantly different between the groups. After 7 days, the average protein intake increased in both groups by 47.5 g; the milk group had higher (Po0.0001) calcium intake; s-OC and s-CTX decreased (Pp0.04) in the milk group (30.9%; 18.7%, respectively) compared with the meat group ( þ 6.4%; 1.0%, respectively) and s-BAP decreased (P ¼ 0.06) both in the milk (3.9%) and the meat group (7.5%). Conclusions: At the equal protein intake, milk, but not meat, decreased bone turnover in prepubertal boys after 7 days. This effect was probably due to some milk-derived compounds, rather than to the total protein intake. Future studies should elucidate the mechanism(s) of milk-related decline of bone turnover and its relevance for peak bone mass during growth. Sponsorship: University PhD scholarships. European Journal of Clinical Nutrition (2007) 61, 957–962; doi:10.1038/sj.ejcn.1602605; published online 17 January 2007 Keywords: bone turnover; milk; meat; protein; prepuberty; boys Introduction The demographic shift towards an older society has in- creased the prevalence of age-related diseases, such as osteoporosis (Ferrari, 2005). The risk of osteoporosis later in life can be reduced by obtaining a high peak bone mass during growth (Baroncelli et al., 2005). Up to 20% of the variation in peak bone mass is affected by lifestyle, including nutrition (Ferrari, 2005). Therefore, it is important to identify nutritional factors that could be used for prevention of osteoporosis. Milk is a rich source of compounds, which appear to benefit bone development (e.g. bioactive peptides, calcium, growth factors). In the large, third National Health and Nutrition Examination Survey (NHANES III), high milk intake during childhood and adolescence correlated (Po0.05) with a greater bone mineral density (BMD) and a lower risk of bone fracture later in life (Kalkwarf et al., 2003). Similarly, present milk intake correlated positively (Po0.05) with bone-mineral acquisition in teenage girls (Du et al., 2002), and milk avoidance was associated (Po0.001) with an increased risk of prepubertal, low-trauma bone fracture in children aged 3–10 years (Goulding et al., 2004). Also, many intervention trials have reported a positive effect of milk on bone mass during growth (Cadogan et al., 1997; Du et al., Received 21 April 2006; revised 4 September 2006; accepted 10 November 2006; published online 17 January 2007 Correspondence: AZ Budek, Department of Human Nutrition, Faculty of Life Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg, Denmark. E-mail: alzb@kvl.dk Guarantor: AZ Budek. Contributors: AZB performed biochemical measurements of markers for bone turnover, conducted the statistical analyses and prepared the manuscript in collaboration with CH, KFM and CM. No author had a financial or personal conflict of interest related to this project. European Journal of Clinical Nutrition (2007) 61, 957–962 & 2007 Nature Publishing Group All rights reserved 0954-3007/07 $30.00 www.nature.com/ejcn