title: High-protein intake enhances the positive impact of physical activity on BMC in prepubertal boys.
abstract: In 232 healthy prepubertal boys, increased physical activity was associated with greater BMC at both axial and appendicular sites under high-protein intake.
  
  
  BACKGROUND
  Physical activity is an important lifestyle determinant of bone mineral mass acquisition. Its impact during childhood can be modulated by nutrition, particularly by protein and calcium intakes. We analyzed the relationship between physical activity levels and protein compared with calcium intake on BMC.
  
  
  METHODS
  In 232 healthy prepubertal boys (age: 7.4 +/- 0.4 [SD] yr; standing height: 125.7 +/- 5.9 cm; body weight: 25.3 +/- 4.6 kg), physical activity and protein and calcium intakes were recorded. BMC was measured by DXA at the radial metaphysis, radial diaphysis, total radius, femoral neck, total hip, femoral diaphysis, and L(2)-L(4) vertebrae.
  
  
  RESULTS
  In univariate analysis, the correlation coefficients r with BMC of the various skeletal sites were as follows: physical activity, from 0.26 (p = 0.0001) to 0.40 (p = 0.0001); protein intake, from 0.18 (p = 0.005) to 0.27 (p = 0.0001); calcium intake, from 0.09 (p = 0.181) to 0.17 (p = 0.007). By multiple regression analysis, the beta-adjusted values remained correlated with BMC, ranging as follows: physical activity, from 0.219 (p = 0.0007) to 0.340 (p < 0.0001); protein intake, from 0.120 (p = 0.146) to 0.217 (p = 0.009). In contrast, it was not correlated for calcium intake: from -0.069 (p = 0.410) to 0.001 (p = 0.986). With protein intake (mean = 2.0 g/kg body weight/d) above the median, increased physical activity from 168 to 321 kcal/d was associated with greater mean BMC Z-score (+0.6, p = 0.0005). In contrast with protein intake (mean = 1.5 g/kg body weight/d) below the median, increased physical activity from 167 to 312 kcal/d was not associated with a significantly greater mean BMC Z-score (+0.2, p = 0.371). The interaction between physical activity and protein intake was close to statistical significance for mean BMC Z-score (p = 0.055) and significant for femoral neck BMC (p = 0.012). In keeping with the results derived from multiple regression analysis, the increased physical activity on mean BMC Z-score was not influenced by difference in calcium intake above (mean = 945 mg/d) and below (mean = 555 mg/d) the median.
  
  
  CONCLUSIONS
  In healthy prepubertal boys, the impact in increased physical activity on BMC seems to be enhanced by protein intake within limits above the usual recommended allowance.
authors: Division of Bone Diseases [WHO Collaborating Centre for Osteoporosis Prevention], Department of Rehabilitation and Geriatrics, University Hospitals of Geneva, Geneva, Switzerland. thierry.chevalley@hcuge.ch
authors: Thierry
authors: T
authors: Chevalley
authors: Jean-Philippe
authors: JP
authors: Bonjour
authors: Serge
authors: S
authors: Ferrari
authors: René
authors: R
authors: Rizzoli
mesh_terms: D015519:Bone Density / Q000187:drug effects / Q000502:physiology*; D002136:Calcium, Dietary / Q000008:administration & dosage; D002648:Child; D004044:Dietary Proteins / Q000008:administration & dosage*; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D018673:Nutrition Policy; D011627:Puberty / Q000502:physiology*
chemical_list: D002136:Calcium, Dietary; D004044:Dietary Proteins