Vitamin D Levels and Prevalence of Vitamin D Deficiency in Turkish Women According to Regions and Age Groups

BACKGROUND This retrospective study explored the possible association of 25-hydroxy vitamin D serum levels with age and region in 44 592 women living in Istanbul, Ankara, Antalya, Kayseri, and Diyarbakır, Turkey between January 2011 and December 2017. MATERIAL AND METHODS A retrospective cohort study was conducted on 44 592 women living in Istanbul, Ankara, Antalya, Kayseri, and Diyarbakır between January 2011 and December 2017. Serum vitamin D levels, measured using chemiluminescent microparticle immunoassay (CMIA) method, were categorized as severe deficiency (<10 ng/mL), deficiency (<20 ng/mL), insufficiency (20-29 ng/mL), and normal (≥30 ng/mL). RESULTS Overall, 25.3% had severe deficiency, 57.7% had deficiency, 22.4% had insufficiency, and 19.9% had normal levels. From 2014 to 2017, the prevalence of vitamin D deficiency (VDD) decreased from 64.2% to 49.4%, while mean vitamin D levels increased from 17.7 ng/mL to 22.4 ng/mL (P<0.001). VDD was most prevalent in Diyarbakır (78.7%) and least in Istanbul (50.5%). Mean vitamin D levels were 14.28 ng/mL in Diyarbakır and 22.07 ng/mL in Istanbul (P<0.001). The 36-50 years age group had the lowest VDD prevalence (54.6%) and the highest mean vitamin D level (20.99±13.88 ng/mL), compared to the 51-65 years age group (20.17±15.28 ng/mL) and the age 18-35 years group (19.38±12.59 ng/mL) (P<0.001). CONCLUSIONS VDD remains highly prevalent among Turkish women. Regional and age-related differences indicate the need for targeted strategies to identify and address risk factors for VDD in this population.