Vitamin D, parathormone, and insulin resistance in children born large for gestational age

Background: Low vitamin D [25(OH)D] levels have been associated with type-2 diabetes mellitus. Children born large for gestational age (LGA) may exhibit increased indices of insulin resistance early in life. Objective: This study aims to prospectively examine serum 25(OH)D and parathormone (iPTH) levels in LGA and appropriate for gestational age (AGA) prepubertal children, in relation to the severity of macrosomia and insulin resistance. Methods: Children were examined at age 5-7.5 years, 38 born LGA and 39 AGA, matched for age, gender, body weight, height and body mass index (BMI). Twenty-one LGA had birth weights in the 90th-97th percentile and 17 >97th percentile. Fasting serum levels of glucose, insulin, 25(OH)D, and iPTH were measured. The homeostasis model assessment for insulin resistance (HOMA-IR) was estimated. Results: The insulin resistance indices were higher in the LGA >97th percentile subgroup than in the AGA group: HOMA-IR 1.53+/-0.66 vs. 1.04+/-0.53 and fasting insulin 6.92+/-3.1 vs. 4.78+/-2.2 mu IU/mL (but similar to the AGA group), and in the LGA 90th-97th percentile subgroup: HOMA-IR 1.17+/-0.61 and insulin 5.53+/-2.2. There was no difference in 25(OH)D among the three subgroups. The iPTH was higher in the LGA >97th percentile subgroup than in the AGA group (26.8+/-7.6 and 22.6+/-7.2 pg/mL, respectively, p<0.05), although it was not correlated with insulin resistance indices. Birth weight was correlated negatively with fasting insulin and HOMA-IR in the entire cohort, independent of age, sex, waist circumference, and BMI (beta=0.37, p<0.01 and beta=0.30, p<0.05, respectively), while waist circumference was positively correlated with HOMA-IR (R=0.40, p<0.001). Conclusion: Birth weight and current body composition appear to affect glucose homeostasis in LGA prepubertal children, while the serum levels of 25(OH)D and iPTH appear to be uninvolved.