Tracking of size-adjusted bone mineral content and bone area in boys and girls from 10 to 17 years of age.

UNLABELLED: Positive correlations for bone mineral content (BMC) between 10 and 17 years of age were found for boys and girls after adjusting for body size, puberty, and diet. This tracking of BMC indicated that osteoporosis prevention should begin already in prepuberty. INTRODUCTION: Previous studies indicate that BMC is tracking during growth, but it remains unclear whether this would remain significant after adjusting for important confounders. We tested the hypothesis that BMC and bone area (BA) track from 10 to 17 years of age, independently of body size, pubertal stage, and dietary intake of energy, calcium and protein. METHODS: A longitudinal study where whole body (T) and lumbar spine (LS) BMC and BA (dual-energy X-ray absorptiometry) and dietary intake (7-day food records) were assessed at 10 and 17 years of age in boys and girls (n = 91). Tracking of bone variables from 10 to 17 years was estimated by Pearson's correlations adjusted for the selected confounders. RESULTS: The unadjusted correlations for T-BMC between 10 and 17 years, likewise for LS-BMC and T-BA, were positive for both sexes (0.51-0.81; P < 0.0001) and remained significant after correcting for the selected confounders. The unadjusted correlations for LS-BA between 10 and 17 years were significant only for girls (0.29; P < 0.05), but not after further corrections. CONCLUSIONS: Bone mass tracks from 10 to 17 years of age in boys and girls, especially after accounting for important confounders, indicating that osteoporosis prevention should begin in early stages of bone development.

High intake of milk, but not meat, decreases bone turnover in prepubertal boys after 7 days.

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 approximately 53 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 (P<0.0001) calcium intake; s-OC and s-CTX decreased (P< or =0.04) in the milk group (-30.9%; -18.7%, respectively) compared with the meat group (+6.4%; -1.0%, respectively) and s-BAP decreased (P=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.

Dietary protein intake and bone mineral content in adolescents-The Copenhagen Cohort Study.

UNLABELLED: Data indicate that various protein sources may exhibit a differential effect on bone metabolism. We investigated associations of milk and meat protein intake with bone mineral content (BMC) in adolescents. Milk, but not meat, protein intake was positively associated with size-adjusted BMC. Milk-derived protein may be beneficial for bone mineralization. INTRODUCTION: Milk and meat protein intake has been reported to exhibit a differential effect on serum insulin-like growth factor-I (IGF-I). IGF-I plays a key role in bone metabolism. Therefore, we investigated associations of different protein sources with BMC and bone area (BA) in adolescents. METHODS: This was a cross-sectional study of 17-year-old girls (n = 63) and boys (n = 46) participating in the second follow-up of The Copenhagen Cohort Study. We measured dietary intake (7-day food record), BMC and BA (dual-energy X-ray absorptiometry), serum markers for bone turnover and serum IGF-I (immunoassays). RESULTS: The mean total protein intake ( approximately 1.2 g/kg) was modestly higher than that recommended. Total and milk ( approximately 0.3 g/kg) protein intake, but not meat protein intake ( approximately 0.4 g/kg), was positively associated with size-adjusted BMC (P