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, ~53% girls; ~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 (~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~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.

The time of day and the interval since previous meal are associated with plasma zinc concentrations and affect estimated risk of zinc deficiency in young children in Peru and Ecuador.

BACKGROUND/OBJECTIVES: Plasma zinc concentration is the preferred biomarker of zinc status, but the time of day and time since previous meals can modify the results. Measuring fasting plasma zinc concentration is not feasible among young children, so adjustments need to be developed for interpreting results. Our objective is to develop correction factors to adjust for the effects of time of day and interval since the previous meal when measuring plasma zinc concentrations of young children. SUBJECTS/METHODS: We measured plasma zinc concentrations among young Peruvian (n =297) and Ecuadorian (n=466) children, and constructed regression models adjusting for time of day, interval since previous meal and infections. RESULTS: Plasma zinc concentrations were positively related to the number of hours since the previous meal in the Peru trial (r =0.22, P<0.0001) and negatively related to the time of day of blood sampling in both Peru (r = -0.24, P<0.0001) and Ecuador (r = -0.18, P<0.001). In multivariate models, plasma zinc concentrations were ~2 µg per 100 ml less for each hour later in the morning when blood samples were collected, in both populations, and concentrations were ~1.0 µg per 100 ml greater for every hour since previous meal consumption in Peru. The percentage of children with low plasma zinc concentrations varied according to both these factors. CONCLUSIONS: The time of day and the interval since the preceding meal should be recorded when measuring plasma zinc concentration and incorporated into the statistical analysis and interpretation when assessing population zinc status.