How deficient are we? A retrospective analysis of vitamin D status in 85,892 Turkish adults

Vitamin D deficiency remains a major global public health concern. This study aimed to assess vitamin D levels measured in individuals aged 18 years and older between 2016 and 2025 in a tertiary care hospital and to examine the association of these levels with seasonal, annual, and demographic variables.

This retrospective observational study included patients who presented to Duzce University Hospital for any reason between 2016 and 2025 and had serum 25(OH)D levels measured. In total, data from 85,892 individuals were analyzed. Vitamin D status was categorized as sufficient (> 30 ng/mL), insufficient (20-30 ng/mL), or deficient (< 20 ng/mL).

Among the participants, 70.2% (n = 60,309) were women and 29.8% (n = 25,583) were men. The mean age was 47.16 ± 17.62 years. The overall mean serum 25(OH)D level was 17.90 ± 12.08 ng/mL. Vitamin D deficiency (< 20 ng/mL) was identified in 68.6% of women and 61.3% of men. Overall, 66.4% (n = 57,051) of participants had Vitamin D deficiency (< 20 ng/mL), 21.7% (n = 18,635) had Vitamin D insufficiency (20-30 ng/mL), and 11.9% (n = 10,206) had sufficient Vitamin D levels (> 30 ng/mL). The mean 25(OH)D level was 19.16 ± 10.74 ng/mL in men and 17.37 ± 12.56 ng/mL in women, with significantly higher levels observed in men (p < 0.001). Participants aged 65 years and older had significantly higher vitamin D levels compared with those under 65 years (p < 0.001). Seasonally, the highest mean vitamin D levels were recorded in summer, whereas the lowest levels were found in winter.

Vitamin D deficiency continues to pose a substantial public health challenge in Turkey. Addressing this issue should be considered a priority, and further comprehensive studies are urgently needed to support the development of effective strategies aimed at reducing deficiency rates.