Age and seasonal variation of serum vitamin D levels in healthy school children and adolescents

Methods We included 706 school children and adolescents aged 7 to 18 years (434 girls and 272 boys) from March 2011 to February 2012. We excluded subjects with any acute or chronic diseases. None of subjects were taking calcium or vitamin D supplements. They were classified according age (elementary school, 7-12 years old, n=565; middle school, 13-15 years old, n=75; high school, 16-18 years old, n=36), sex (boys, n=272; girls, n=434) and season (spring, March to May, n=267; summer, June to August, n=106; fall, September to November, n=139; winter, December to February, n=194). We performed anthropometric measurement and laboratory tests including fasting lipid profile (cholesterol, triglyceride and LDL cholesterol), ALP, Ca, P and serum 25OHD3 level. Vitamin D deficiency were defined as a serum 25OHD3 level lesser than 20 ng/mL.