Assessment of vitamin D status in healthy children and adolescents living in Tehran and its relation to iPTH, gender, weight and height

This study was conducted to determine the frequency of vitamin D deficiency and its correlation with different factors. Three hundred and thirteen healthy children and adolescents (192 females and 121 males aged 8-18 years, mean +/- SD, 12.7 +/- 2.3 years) were enrolled, and measurements of serum 25-hydroxyvitamin D [25(OH) D] (using EIA) and intact parathyroid hormone (iPTH) (using immunoradiometric assay (IRMA)) were conducted. The grades of vitamin D status were defined according to blood level of 25(OH) D as follows: severely deficient < 12.5; deficient, >= 12.5 and < 25; insufficient, >= 25 and < 50; normal >= 50 and < 250 nmol/L. Severe deficiency was detected in 25% of subjects (males 8%; females 92%), deficiency in 27% (males 34%; females 66%) and insufficiency in 26% (males 58%; females 42%). The mean 25(OH) D level in males was significantly greater than that in females (p < 0.001), and this level was significantly higher in prepubertal compared to pubertal subjects (p < 0.001). 25(OH) D had a negative correlationwith iPTH(p < 0.001). The curve of iPTH began to rise when 25(OH) Dreached 75 nmol/L. The level of 25(OH) D had a negative correlation with BMI-SDS and height-SDS in females (p-value, 0.01 and 0.039, respectively). The subjects did not have any signs or symptoms of rickets. Frequency of vitamin D deficiency did not have any significant seasonal variation. Furthermore, vitamin D deficiency was not found to be related to the type or location of the subjects' homes. In this study, subclinical vitamin D deficiency was significantly more prevalent in females, particularly those undergoing puberty. Children who were obese and taller than average, had lower levels of 25(OH) D, and level of 25(OH) D should be maintained > 75 nmol/L in order to prevent PTH rising.