To investigate the frequency of vitamin D deficiency in relation to demographics, clinical diagnosis, season of measurement and laboratory parameters in adult out-patients.

Descriptive, retrospective study concerning evaluation of the initial 25-hydroxyvitamin D (25(OH)D) levels determined at admission in relation to demographics, clinical diagnosis, season of measurement and laboratory parameters. 25(OH)D levels <20 ng/ml were classified as deficiency, 20–30 ng/ml as insufficiency and >30 ng/ml as sufficiency.

Out-patient clinics at a tertiary care centre.

A total of 2488 adult patients (mean age: 53·3 (sd 15·2) years; 85·2 % were females) admitted to out-patient clinics at Baskent University Istanbul Hospital were included.

Mean level of 25(OH)D in the overall population was 17·4 (sd 11·5) ng/ml while insufficiency and deficiency were evident in 24 % and 66 % of patients, respectively. Mean 25(OH)D levels in males >45 years old were higher than in their female counterparts (19·4 (sd 11·3) ng/ml v. 17·8 (sd 12·2) ng/ml; P < 0·05). Mean 25(OH)D levels obtained in summer (18·6 (sd 11·1) ng/ml) and autumn (23·3 (sd 13·6) ng/ml) were significantly higher than levels in spring (16·1 (sd 10·3) ng/ml) and winter (14·6 (sd 10·2) ng/ml; P < 0·01). Mean 25(OH)D levels were determined to be significantly lower in obese patients compared with non-obese patients (15·6 (sd 10·4) ng/ml v. 17·6 (sd 11·6) ng/ml; P < 0·05). Levels of 25(OH)D were significantly negatively correlated with serum parathyroid hormone levels (r = −0·194; P < 0·001) while significantly positively correlated with phosphorus (r = 0·059; P < 0·01) and HDL cholesterol (r = 0·070; P < 0·01) levels.

Our findings indicate that vitamin D deficiency is very common among out-patients in Turkey, regardless of gender and age, especially among obese people and during winter and spring.