Background

The associations of vitamin D with regional fat distribution, a key determinant of adiposity phenotypes, remains uncertain. To examine the associations between regional fat distribution and plasma 25-hydroxyvitamin D (25[OH]D) levels in Chinese school-aged children and to explore the possible mediating role of insulin resistance (IR).

Methods

A population-based, nationwide and multicenter cross-sectional study involving 6,589 pediatric participants (49.9% boys) aged 6-18 years. Body regional fat mass assessed by dual-energy x-ray absorptiometry, and plasma 25(OH)D concentrations were measured. Sufficient vitamin D defined as 25(OH)D ≥ 50 nmol/L. IR as determined by the homeostasis model (HOMA-IR).

Results

Among boys, after adjustment for multiple variables including other regional fat mass index variables, higher trunk fat mass index and android fat mass index were associated with greater odds of vitamin D insufficiency (OR=2.14 and 1.87, respectively), while extremity fat mass index and gynoid fat mass index were associated with protective ORs for vitamin D insufficiency (OR=0.63 and 0.71, respectively, all P <0.05). Mediation analyses indicated that these associations were mediated by HOMA-IR, the proportions via the mediation were 1.65% ~ 10.14%. Consistently, increased central fat distribution (e.g., trunk fat to total fat ratio, android fat to total fat ratio) and decreased peripheral fat distribution (e.g., extremity fat to total fat ratio, gynoid fat to total fat ratio) were associated with greater odds of vitamin D insufficiency. Among girls, however, the associations of regional body fat with vitamin D and the mediations by IR were weaker than in boys, and most of these analyses did not reach statistical significance.

Conclusions

Regional body fat deposits were associated with vitamin D nutritional status in Chinese children. The associations with vitamin D appear to be more pronounced among boys, and could be explained, at least partially, by IR.