Seasonal variation of serum 25 hydroxy D3 in residents of Tehran

Background and aim: vitamin D is essential for bone health. It has been shown that in many communities serum levels of vitamin D can be subject to seasonal variations but so far no study has been conducted on this variable in natives of Tehran. Subjects and Methods: 1172 natives of Tehran, 682 women and 490 men, aged 3–69 yr entered the study. Sampling was performed monthly except during Ramadhan, the holy month of Islamic fasting. Serum 25-hydroxyvitamin D (25-OHD) was measured using protein binding assay and levels below 20 ng/ml were determined as vitamin D deficient. Results: serum 25-OHD concentrations showed monthly variations in both sexes but the magnitude of variations was more pronounced in men. The nadir of serum levels in both sexes were seen in December and February, 12±13 and 14±14 ng/ml in women, and 28±16 and 24±18 mg/ml in men, respectively with the highest values being seen in October; 29±29 ng/ml in women and 55±27 ng/ml in men. During the whole period of study the maximum values for women were either equal or less than the minimum values for men. The values for men during summer and winter (31±17 and 28±22 ng/ml, respectively) were significantly lower than the values for spring and fall (38±27 and 43±29 ng/ml respectively). In women there was no significant difference in the values of the first three seasons and only the values pertaining to winter were significantly different from the values of fall.