CONTEXT: Peak bone mass (PBM) and strength are important determinants of fragility fracture risk in later life. During growth bone is responsive to changes in nutrition and physical activity (PA), particularly when occuring before pubertal maturation.
OBJECTIVE: In prepubertal healthy boys, protein intake (Prot-Int) enhances the impact of PA on weight-bearing bone. We hypothesized that the synergism between Prot-Int and PA on proximal femur as recorded at mean age of 7.4 years would track until PBM.
METHODS: 124 boys were followed from 7.4 to 15.2 and 22.6 years. At 7.4 years they were dichotomized according to the median of both PA and Prot-Int.
RESULTS: In boys with PA > Median (310 vs 169 kcal.d(-1)), higher vs low Prot-Int (57.7 vs 38.0 g.d(-1)) was associated with +9.8% greater femoral neck (FN) BMC (P=0.027) at 7.4 years. At 15.2 and 22.6 years, this difference was maintained: FN BMC: +12.7% (P=0.012) and +11.3% (P=0.016), respectively. With PA > Median, in Prot-Int > vs < Median, differences in FN BMC Z-scores were +0.60, +0.70 and +0.68 at 7.4, 15.2 and 22.6 years, respectively, and also associated with greater FN width. Micro-finite element analysis of the distal tibia at 15.2 and 22.6 years indicated that in the two groups with PA > Median, CSA, stiffness and failure load were greater in Prot-Int > vs < Median.
CONCLUSIONS: This study demonstrates the crucial influence of Prot-Int on the response to enhanced PA and the importance of prepubertal years for modifiying, by environmental factors, the bone growth trajectory and, thereby, for achieving higher PBM and greater strength in healthy male subjects.