Optimal level of 25-(OH)D in children in Nanjing (32°N Lat) during winter

The optimal serum level of 25-hydroxyvitamin D (25-(OH)D) for bone health is still unclear, especially in children. Hypovitaminosis D is also re-emerging in developed and developing countries. The purpose of the present study was therefore to determine optimal serum 25-(OH)D level and preliminarily identify the vitamin D nutritional status in Nanjing children.

All subjects (76 healthy, 66 suffering from infectious diseases) aged 0-10 years were recruited during the period December 2007-March 2008. Venous blood samples were collected before breakfast and the levels of serum 25-(OH)D, parathyroid hormone (PTH), bone-specific alkaline phosphatase (BAP), calcium (Ca), phosphorus (P) were determined. The optimal level of serum 25-(OH)D was explored using the three response curves of 25-(OH)D versus PTH, 25-(OH)D versus BAP, and 25-(OH)D versus Ca×P product.

For 25-(OH)D ≤ 50 nmol/L, PTH and BAP were both inversely correlated with 25-(OH)D (PTH, r=-0.864, P < 0.01; BAP, r=-0.856, P < 0.01). For 25-(OH)D > 50-60 nmol/L, levels of PTH and BAP remained steady. With regard to the Ca×P product, for 25-(OH)D ≤ 50 nmol/L, Ca×P product increased as 25-(OH)D increased (r= 0.037, P > 0.05). For 25-(OH)D > 50-60 nmol/L, Ca×P product remained steady. The mean serum level of 25-(OH)D was 80.5 ± 29.3 nmol/L (mean ± SD) in the healthy children, and 65.7 ± 32.3 nmol/L in the sick children.

The optimal 25-(OH)D level may be 50-60 nmol/L for bone health in Nanjing children. The vitamin D nutritional status of Nanjing children is relatively good in winter.