Introduction
Vitamin D deficiency is a major public health problem worldwide in all age groups. Low serum vitamin D levels have been associated with adverse clinical outcomes; identifying and treating deficiency may improve outcomes. The estimated prevalence of vitamin D levels below 20 ng/mL was previously reported as 37% in world overview [1], 72% in China [2], 26% in US [3], 40% in Europe [4], 37% in Canada [5], and 24% in US [6, 7]. In a meta-analysis from Turkey vitamin D, deficiency/insufficiency rates were 63.5% among adults [8]. Vitamin D deficiency was found to be higher in specific groups, such as subjects from nursing homes [9], long-term indoor healthcare workers [10], and patients with obesity and diabetes [11, 12].
Vitamin D deficiency is related to chronic diseases, the tendency of some infections, and worsening of infections [13]. Treating vitamin D deficiency is cheap, and treating deficiency may improve some clinical outcomes of chronic diseases and infections. Diagnosis and treatment of vitamin D deficiency and toxicity depend on laboratory measurements of 25(OH) D levels [14]. Vitamin D deficiency is relatively more common in hospital admitted patients, and an inverse relationship between the frequency of vitamin D deficiency and hospital admission had been reported [15]. In Rai et al. study [16] and Amrein, et al. study [17], vitamin D deficiency was detected in 73.6% and 60.2% of tertiary care center admitted patients, it was 71.23% among 6957 patients from secondary care hospital laboratory [8], and it was found as 65.4% in a general hospital from India [18].
Vitamin D levels vary seasonally, usually increase from spring to summer and decrease afterward. Aging, female gender, increased skin pigmentation, higher latitude, winter season, less sunlight exposure, topical application of sunscreen, dietary habits, obesity are found to be associated with lower 25(OH) D levels [14, 19, 20]. Also, the hospital admitted patients affected from seasons, in Sezgin et al. study vitamin D levels were higher in summer compared to winter [21]. In line with previous reports, in Amrein et al study [17] vitamin D deficiency was higher in winter compared to summer and autumn.
We hypothesize that the frequency of vitamin D deficiency in subjects who are admitted to hospitals is higher than the general population, and vitamin D intoxication is also higher than reported. This study aimed to evaluate the nationwide prevalence of vitamin D status in tertiary care hospitals in Turkey. We determined age and gender-related rates of vitamin D insufficiency, deficiency, and hypervitaminosis D in adult subjects admitted to tertiary care hospitals.