Are there any seasonal variations in 25-hydroxyvitamin D and parathyroid hormone serum levels in children and adolescents with severe obesity?

The objective of this study was to analyze the prevalence of hypovitaminosis D in children with severe obesity. We hypothesized that severe obesity could modify the seasonal variations in 25(OH)D and PTH serum levels throughout the year. A cross-sectional clinical and blood testing (calcium, phosphorus, 25(OH)D, and PTH) was carried out in 282 patients with severe obesity, aged 7.2-15.2 years. A control group was recruited (348 healthy children, aged 7.1-14.9 years). The criteria of the US Endocrine Society were used for the definition of hypovitaminosis D. Vitamin D deficiency and hyperparathyroidism were more frequent (p < 0.05) in the obesity group (44.5 vs. 11.5% and 22.4 vs. 3.9%, respectively). There were seasonal variations in 25(OH)D levels in the obesity group, but they were lower (p < 0.05) with respect to the control group. In contrast, PTH levels were higher (p < 0.05) in the obesity group with respect to the control group, but there were no significant seasonal variations in PTH levels. Conclusion: Suboptimal vitamin D status and high levels of PTH are a common feature in pediatric population with severe obesity. In these patients, the seasonal variations in 25(OH)D were not modified, and PTH levels remained increased throughout the year, but without any seasonal variations.