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 52Ê30" N, 32 52Ê 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.