Higher daily physical activity is associated with higher osteocalcin levels in adolescents

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. PURPOSE 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.