Serum 25-Hydroxyvitamin D associated with indicators of body fat and insulin resistance in prepubertal chilean children

BACKGROUND: Consistent data on the relation between vitamin D, body fat and insulin resistance (IR) in children are lacking. OBJECTIVES: (1) To evaluate the association between serum 25-Hydroxyvitamin D [25(OH) D] and key indicators of: adiposity (total and central), IR, and (2) to estimate serum 25(OH) D cut-offs that best reflect IR and total and central adiposity in children. SUBJECTS/METHODS: Prepubertal children (n = 435, similar to 53% girls; similar to age 7 years) from the Growth and Obesity Chilean Cohort Study were evaluated for potential associations between serum 25(OH) D and indicators of: (1) total adiposity (body mass index by age (BAZ), body fat (including three-component model)), central adiposity (waist circumference and trunk fatness); (2) IR (homeostasis model assessment of IR) and insulin sensitive (quantitative insulin sensitivity check index) using standardized multiple regression models with standardized coefficients and receiver operating characteristic curves. RESULTS: Overall, mean serum 25(OH)D was 32.1 +/- 9.2 ng ml(-1), while 19.4% of children were obese (BAZ >= 2 s.d.). Serum 25(OH)D was inversely associated with indicators of total and central adiposity and with IR indicators. Effect sizes were moderate in girls (similar to 0.3 for adiposity and IR indicators), while, weaker values were found in boys. Serum 25(OH)D estimated cut-offs that best predicted total, central adiposity and IR were similar to 30 ng ml(-1). Children with suboptimal serum 25(OH)D (<30 ng ml(-1)) had a higher risk (two to three times) of being obese (high BAZ, body fat percent and/or central adiposity); and three to four times greater risk for IR. CONCLUSIONS: Serum 25(OH) D was inversely associated with adiposity (total and central) and IR indicators in prepubertal Chilean children. The conventional cut-off of vitamin D sufficiency (>= 30 ng ml(-1)) was adequate to assess obesity and IR risk in this age group.