Background: Decreased serum 25-hydroxyvitamin D (25-OHD) level has frequently been reported in obesity, a condition which is associated with insulin resistance. Insulin resistance was negatively associated with serum 25-OHD. Puberty is the period with altered insulin sensitivity. Previous studies showed conflicting results of the variation of serum 25-OHD levels across pubertal stages. However, data on serum 25-OHD levels across pubertal stages in obese children are limited.
Objective: To determine serum 25-OHD levels and insulin sensitivity across pubertal stages in obese children
Methods: There were 230 obese children, aged 11.4 (2.5) years, enrolled. All children underwent an OGTT and had serum 25-OHD, Ca, P and intact parathyroid hormone (iPTH) levels measured. All children were classified into 3 groups of puberty; Tanner I (N = 62), Tanner II & III (N = 88) and Tanner IV & V (N = 80). Insulin sensitivity indices [whole body insulin sensitivity index (WBISI) and homeostatic model assessment of insulin resistance (HOMA-IR)] and β-cell function indices [HOMA-β and insulinogenic index (IGI)] were calculated from serum glucose and insulin levels derived during the OGTT.
Results: Mean (SD) 25-OHD level was 26 (7) ng/mL. Despite being less obese with advanced stages of puberty [BMI Z-scores for Tanner I, II & III and IV & V: 2.9 (2.4, 3.7), 2.4 (2.1, 3.0) and 2.2 (1.8, 2.5), respectively, p <0.001], serum 25-OHD were progressively decreased [30 (6), 26 (7) and 23 (6) ng/mL, p <0.001]. Differences in calciotropic parameters were also observed among the 3 groups [iPTH: 31 (25, 38), 35 (29, 46) and 40 (32, 53) pg/mL, p <0.001; Ca: 9.6 (9.4, 9.8), 9.6 (9.2, 9.8) and 9.3 (9.0, 9.6) mg/dL, p = 0.002]. Changes of insulin sensitivity did not follow the same pattern as that of serum 25-OHD with maximum insulin resistance observed during Tanner stages II & III [WBISI: 3.0 (1.9, 4.8), 2.1 (1.6, 3.3) and 3.3 (2.0, 4.3), p <0.001; HOMA-IR: 2.5 (1.5, 3.9), 3.1 (2.1, 4.5) and 2.6 (1.8, 3.8), p = 0.021]. After adjustment for age, sex and BMI Z-score, puberty was negatively associated with serum 25-OHD. However, insulin sensitivity and β-cell function indices were not associated with serum 25-OHD.
Conclusion: Progressive decrease in serum 25-OHD level was observed with more advanced stage of puberty in obese children and did not follow the same pattern as that of insulin sensitivity. Therefore, the changes of serum 25-OHD were unlikely related to insulin sensitivity.
19 - 21 Sep 2019
European Society for Paediatric Endocrinology