Objective: We aimed to establish reference ranges of 25(OH) vitamin D levels in childhood and adults including age-sex-specific partition, also to evaluate the seasonal variations.

Material and Method: The study comprised one hundred eighty-one thousand six hundred sixteen venous blood samples from residual material of the Istanbul Public Health Laboratory workflow. The study group was stratified according to age groups; Group 1; 0-2, group 2; 3-10 years, group 3; 11-20 years, group 4; 21-50 years group 5; 51-70 years and group 6; over 70 years of age.

Results: 25(OH) vitamin D concentration of all study group was 21.7±13.3 ng/mL, being significantly lower in women compared with men (21.35±13.52 ng/mL vs 22.54±12.5 ng/mL, p=0.008). In entire group, the deficiency rate was 43.8%, and 44.0%, the insufficiency rate was 29.4% and 34.8%, and severe deficiency rate was 11.4% and 4.9% for women and men respectively. The severe deficiency, insufficiency and sufficiency rates were significantly different between females and males (p=0.000 for all). The lowest deficiency rate was in 0-2 age group, 25.2% and 14.6%, and the highest in 11-20 year age group (57.2% and 54.4%). The deficiency rates were significantly different except the subjects over 70 years. The vit-D levels of March was significantly lower than October (p=0.001).

Conclusion: Serum 25 (OH) vit-D levels contribute greatly to clinical practice throughout the lifetime. Serum vit-D determination should be measured periodically especially in childhood, adolescence and adulthood, and legally mandatory food supplementation may meet a great contribution for public health.

25(OH) vitamin D deficiency Age groups Seasonal variation