Vitamin D status and seasonal changes in plasma concentrations of 25-hydroxyvitamin D in office workers in Ankara, Turkey.

Background: Lack of sun exposure is one of the primary causes of epidemic vitamin D deficiency worldwide. The aim of this study was to investigate vitamin D status and seasonal changes in summer and winter in office workers.

Methods: This study was conducted in Ankara located at 39° 52' 30" N, 32° 52' E. The study consisted of 118 premenopausal women and men aged between 21 and 52 years-old. Seasonal changes were evaluated in August and February. Fasting serum was obtained for intact parathyroid hormone (iPTH) and 25-hydroxyvitamin D (25OHD). Additional data were collected by a questionnaire that enquired about age, weight, height, wearing style, dietary calcium intake and sunlight exposure. Serum 25OHD concentration was measured using a precise HPLC assay. Low vitamin D status was defined as a 25OHD concentration less than 30 ng/mL.

Results: Mean serum 25OHD concentration in summer was 28.4±10.4 ng/mL and 13.8±6.6 ng/mL in winter (p<0.001). 35.6% of the subjects were vitamin D insufficient in summer and 12.7% in winter (p<0.001) while 31.5% were vitamin D deficient in summer and 83.9% in winter (p<0.001). A significant increase in iPTH levels (33.1±15.9 pg/mL vs 49.6±24.3 pg/mL, p<0.001) was observed throughout the seasonal change. No significant association was found between 25OHD levels and iPTH, body mass index, age and sun exposure index (p>0.05 for all) in both seasons.

Conclusion: Vitamin D deficiency is very prevalent in office workers even in summer time and this should be accepted as a public health problem.