Prepubertal Impact of Protein Intake and Physical Activity on Weight-Bearing Peak Bone Mass and Strength in Males

Context Peak bone mass (PBM) and strength are important determinants of fracture risk in later life. During growth, bone is responsive to changes in nutrition and physical activity (PA), particularly 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 7.4 years would track until PBM. Methods A total of 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 greater than the 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) bone mineral content (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 greater than the median, in Prot-Int greater than vs less than the 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. Microfinite element analysis of distal tibia at 15.2 and 22.6 years indicated that in the 2 groups with PA greater than the median, cross-sectional area, stiffness, and failure load were greater in Prot-Int greater than vs less than the median. Conclusions This study demonstrates the crucial influence of Prot-Int on the response to enhanced PA and the importance of prepubertal years for modifying the bone growth trajectory and, thereby, for achieving higher PBM and greater strength in healthy male participants.