Context:

Childhood obesity disproportionately affects Hispanic youth. The skeletal system appears to be a target organ of the adverse effects of obesity. Yet, the relationship between adiposity and bone health in youth and the modulating factors are not well understood.

Objective:

To examine the relationship between adiposity, insulin resistance, cardiorespiratory fitness (CRF) and bone mass in Hispanic youth.

Design:

Cross-sectional design from the Viva La Familia Study.

Setting:

Children’s Nutrition Research Center.

Participants:

A total of 951 Hispanic youth (50% male), 4 to 19 years of age.

Main outcomes and measures:

Bone mineral content (BMC) and density (BMD), lean mass, total body fat mass (FM), truncal FM were obtained using DXA. Fasting glucose and insulin were obtained and the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. CRF was measured using a treadmill ramp protocol. We applied linear regression models and mediation analyses.

Results:

Adiposity measures were negatively related to BMC and BMD after accounting for lean mass and sex. Insulin resistance negatively contributed whereas CRF positively contributed to the variance in BMC and BMD, more notably in the pubertal age group. In mediation analysis, HOMA-IR partially mediated the negative relationship of adiposity to BMC [standardized indirect effect (IE) = -.0382; 95% CI = (-.0515, -.0264)] whereas the sequential indirect effect of HOMA-IR and CRF partially attenuated [IE= -.0026; 95% CI = (-.0053, -.0005)] this relationship. Similar findings were seen with BMD as the primary outcome.

Conclusions:

Insulin resistance mediates the negative relationship between adiposity and bone mass whereas CRF may partially attenuate it.