title: Higher daily physical activity is associated with higher osteocalcin levels in adolescents.
abstract: BACKGROUND
  Exercise stimulates bone remodeling and improves insulin sensitivity (Si), even without associated weight loss. Osteocalcin (OCN), a bone-derived protein, is associated with improved Si.
  
  
  OBJECTIVE
  We examined how daily physical activity is associated with OCN and Si.
  
  
  METHODS
  Physical activity was measured through questionnaires completed in Minneapolis from 2010-2012. A physical activity score (PAQsum) was calculated to quantify physical activity (range 1-5). OCN and bone specific alkaline phosphatase (BAP) were measured by ELISA. Si was measured by the insulin modified frequently sampled IV glucose tolerance test.
  
  
  RESULTS
  The mean PAQsum value was 2.4±0.8 in 47 participants (12-17.9 years old). PAQsum was positively associated with OCN (p= 0.006). Participants with PAQsum<2 had significantly lower OCN levels compared to participants with PAQsum>2 (p<0.02). Obesity did not modify the association between PAQsum and OCN. There was no statistically significant association between PAQsum and Si or between OCN and Si, even after adjustment for percent body fat.
  
  
  CONCLUSIONS
  OCN is higher in more physically active individuals. More research is needed to clarify the relationship between OCN, physical activity and Si.
authors.affiliation: University of Minnesota, Department of Pediatrics, Division of Endocrinology, 2450 Riverside Dr, East Bldg., MB 677, Minneapolis, MN USA 55454.
authors.forename: Saydi E
authors.initials: SE
authors.lastname: Chahla
authors.affiliation: Barbara Davis Center for Childhood Diabetes, University of Colorado, 1775 Aurora Court, Rm 1306, Aurora, CO, USA, 80045.
authors.forename: Brigitte I
authors.initials: BI
authors.lastname: Frohnert
authors.affiliation: University of Minnesota, Division of Biostatistics, School of Public Health, Biostatistics, MMC 303, 420 Delaware Street S.E. Minneapolis MN USA 55455.
authors.forename: William
authors.initials: W
authors.lastname: Thomas
authors.affiliation: University of Minnesota, Department of Pediatrics, Division of Epidemiology and Clinical Research and Division of Diabetes, Endocrinology and Metabolism, and Department of Medicine, MMC 715, 420 Delaware St SE, Minneapolis, MN USA 55455.
authors.forename: Aaron S
authors.initials: AS
authors.lastname: Kelly
authors.affiliation: University of Minnesota, Department of Pediatrics, Division of Endocrinology, 2450 Riverside Dr, East Bldg., MB 677, Minneapolis, MN USA 55454.
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Nathan
authors.affiliation: Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Department of Pediatrics, Division of Endocrinology, Torrance, CA USA.
authors.forename: Lynda E
authors.initials: LE
authors.lastname: Polgreen
keywords: adolescents; obesity; osteocalcin; physical activity