BACKGROUND:Anemia and vitamin D deficiency are two important public health issues that may accompany many acute and chronic diseases. Several studies conducted in recent years have suggested that vitamin D deficiency is associated with anemia in healthy and patient populations. The aim of the study is to investigate the relationship between vitamin D deficiency and anemia. METHODS:The data of 9,590 adults aged 18 - 64, who applied for periodic medical examination to family medicine polyclinics of a training hospital between 2016 and 2018, were evaluated retrospectively. Individuals were classified into three groups as iron deficiency, iron deficiency anemia, and anemia; and 25 hydroxy vitamin D (25(OH)D) levels were classified into three groups as deficiency, insufficiency, and sufficiency. The groups were compared with respect to study parameters. RESULTS:Of the participants, 2,395 were male (25.0%) (mean age = 43.75 ± 13.43) and 7,195 (75.0%) were female (mean age = 42.93 ± 12.85). The number of anemic patients was 1,470 (15.3%) while the number of patients having no symptoms of anemia was 8,120 (84.7%). Serum hemoglobin (Hgb), iron, and ferritin levels were found to be significantly lower in the group with 25(OH)D deficiency than in the group of those with no deficiency. The mean 25(OH)D levels were observed to be significantly lower in those having anemia (17.4 ng/mL) than in those who do not (20.2 ng/mL), in those having iron deficiency (18.2 ng/mL) than in those who do not (20.5 ng/mL), and in those having iron deficiency anemia (16.6 ng/mL) than in those who do not (20.1 ng/mL) (all p-values are < 0.001). CONCLUSIONS:The findings of this large study population, who live in a Mediterranean city which is sunny for 300 days of the year, indicate that 25(OH)D deficiency is significantly associated with iron deficiency and/or anemia.