Abstract

The main role of Vitamin D is to regulate calcium metabolism, whose main source is vitamin D3 obtained mostly from the action of ultraviolet (UV) light on the skin. Objective: To evaluate the seasonal differences in the concentrations of 25-hydroxy-vitamin D3 (25OHVitD3), parathyroid hormone (PTH), alkaline phosphatase (ALP), and calcium in school-age children. Subjects and Method: The concentrations of 25OHVitD3, PTH, ALP, and calcium were measured in children from Santiago, Chile (latitude -33.4372), aged 5 to 8 years, without Vitamin D supplementation, in different seasons of the year. VitD status was defined as sufficient with concentrations of 25OHVitD3 >20 ng/mL (50 nmol/L), insufficient 12-20 ng/mL (30-50 nmol/L) and deficient 12 ng/mL (30 nmol/L) based on the recommendations of the expert group of the "Global Consensus for the Prevention and Management of Nutritional Rickets". Results: 133 children participated (89 preterms under or equal to 32 weeks), 41 during summer, 28 in fall, 35 in winter, and 29 in spring. The difference of means between summer and winter was 9.6 ng/mL for 25OHVitD3 (p 0.0001), -11.1 pg/mL for PTH (p 0.0001), and -47.5 IU/mL for ALP (p= 0.01). There were no differences in calcium concentrations. In summer, 97.6% of the subjects were classified with sufficiency status (> 20 ng/mL), which decreased significantly in winter to 54.3% (p 0.0001). Conclusions: In winter, 25OHVitD3 concentrations decreased in approximately half of the children, which was associated with an increase in PTH and ALP, and normal calcium concentrations. According to our results, children may need VitD supplementation during fall and winter.