Predictors of calcium retention in adolescent boys.

CONTEXT

The relationship between calcium (Ca) intake and Ca retention in adolescent boys was recently reported.

OBJECTIVE

This study evaluated the influence of Ca intake, serum hormone levels, biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness on Ca retention in the same sample.

DESIGN

This study was a randomized, cross-over design that consisted of two 3-wk metabolic balance periods.

SETTING

The study took place on a university campus as a summer camp.

PATIENTS OR OTHER PARTICIPANTS

A total of 31 American white boys (13-15 yr) participated in the study.

INTERVENTIONS

Each subject consumed a controlled diet with one of five high-low Ca intake pairs that ranged from 670-2003 mg/d, which was manipulated utilizing a fortified beverage.

MAIN OUTCOME MEASURES

Ca retention was determined by Ca intake minus urinary and fecal Ca excretion during each balance period.

RESULTS

Ca intake explained 21.7% of the variability in Ca retention, and serum IGF-I concentration explained an additional 11.5%. Other serum hormone levels did not significantly add to the model. Biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness were not significant predictors of Ca retention in adolescent boys.

CONCLUSIONS

IGF-I, a regulator of growth during puberty, is an important predictor of Ca retention in adolescent boys. However, dietary Ca intake is an even greater predictor of Ca retention during this period of growth.