Discussion
Our study confirms previous reports that vitamin D insufficiency and deficiency are common in the tertiary care hospital admitted subjects, which affected 57.8% of our cohort. Severe vitamin D deficiency was observed in 25% and toxic levels in 0.8% of the cohort. While the highest vitamin D levels were detected in subjects aged between 60 and 79 years, the frequency of vitamin D deficiency was similar between the age groups. Median 25(OH)levels and vitamin D deficiency frequencies were similar between women and men in the whole group. Median 25(OH)D levels in summer and autumn were higher than spring and winter in the whole cohort. To date, this is the largest study of vitamin D status among hospital admitted patients in Turkey.
The levels of vitamin D below 30 ng/mL have been reported in a wide range of distribution; ranged between 26.4% to 77.7 % in the literature [14, 25-28]. While in Korea National Health and Nutrition Examination Survey (KNHANES) 65.7% of males and 76.7% of females had deficient vitamin D levels [29], it was detected in 55.4% and 59.2% of males and females, respectively, in our study. Delos Reyes et al. study which included 15708 subjects admitted to tertiary care hospitals reported that the vitamin D deficiency rate was 11.2%, insufficiency was 32.4% and sufficiency was 56.4% [28]. Vitamin D deficiency was detected in 73.6% and 60.2% of tertiary care center hospitalized patients [16, 17]. While severe deficiency was reported as 26.9% [30], 20.8% [31], 11.2% [28] in previous reports, it was 25 % in our study. In our study sufficient vitamin D levels were detected in 20.3% of patients, while it was ranged between 2.7 to 56.4% in the literature [28, 31].
Similar to previous reports [28, 29, 31], in our study, 25(OH)D levels were higher in older subjects compared to subjects aged below 30 years. Vitamin D deficiency in the young adult group is related to decreased outdoor activities and aggressive sun protection [14]. We attribute the higher levels of 25(OH)D in the elderly population to the representation of the elderly population in this cohort is low, and to the supplementation of vitamin D in this group.
In Forrest et al. study, which evaluated data from 2005 to 2006 of NHANES, the subjects aged between 55 to 59 and 60 to 64 had the highest prevalence rate of vitamin D deficiency [19]. On the other side, in Basile et al. study, subjects aged ≤45years or 46-64 years had higher vitamin D levels compared to those older than 65 years [26].
There controversial results about the effect of gender on vitamin D deficiency. Similar to Forrest et al. study [19], we found that vitamin D levels were similar both in men and women. In Yu et al. [31] and Muscogiuri et al. [12] studies, women had lower vitamin D levels than men. In Hilger et al. study, 25(OH)D levels in women tended to be lower, especially in the Asia/Pacific and Middle East/Africa regions [1]. Contrary to this, in Basile [26] and Delos Reyes [28] et al. studies, vitamin D levels were significantly higher in women than in men [26, 28].
In line with previous reports the median 25(OH)D levels varied significantly according to the seasons, deficiency was found to be most prevalent in spring and winter compared to other seasons [5, 14, 30-33].