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Endokrynol Pol. 2011;62(3):249-51.

Vitamin D deficiency prevalence in summer compared to winter in a city with high humidity and a sultry climate.

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Department of Internal Medicine, Mazandaran University of Medical Sciences, Sari, Iran.



Vitamin D deficiency is high in winter because of reduced exposure to sunlight. It seems that in places with high humidity and a sultry climate, exposure to sunlight in summer can be low too. This study was designed to determine the vitamin D deficiency prevalence in Sari, a city with a high humidity climate at the end of summer, and compare it to winter.


This cross-sectional study was carried out on men and women aged 10 to 70. Clustered blood samples were received from 351 subjects who participated in this study toward the end of summer, and in winter. The levels of serum vitamin D, calcium, phosphorus, alkaline phosphatase and PTH were measured. T test and X2 were used for data analysis.


351 subjects (66.4% women, 33.6% men) aged 11 to 69 (mean age ± SD 37.11 ± 12.6) participated in the study. The mean 25-(OH) D concentration in summer was 13.41 ± 13, and in winter it was 11.7 ± 11, and the difference was statistically significant (p < 0.02). The prevalence of 25-OHvitamin D deficiency was 87.5% (307) in winter and 78.6% (276) in summer (p < 0.05).


This study shows that although in this area with a high humidity climate, seasonal variation of vitamin D is statistically significant, the prevalence of Vitamin D insufficiency is as high in summer as in winter.

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