Vitamin D Levels in Middle-Aged Patients with Obstructive Sleep Apnoea Syndrome

Background: Vitamin D (Vit D) insufficiency has been implicated in the pathophysiology of numerous diseases. Obstructive sleep apnoea syndrome (OSAS), a disorder associated with increased cardiovascular and cerebrovascular morbidity, has been associated with decreased Vit D levels, but reports are inconclusive. Aim: To evaluate the association between serum 25-hydroxyvitamin D [25(OH)D], a marker of Vit D status, with anthropometric and sleep characteristics of OSAS patients and to compare those levels between OSAS patients and non-apnoeic controls. Method: Consecutive subjects who had undergone polysomnography and pulmonary function testing were divided into controls (apnoea-hypopnea index, AHI <5/h) and OSAS group (AHI ≥5/h). Results: A total of 169 subjects (135 men) were included. OSAS patients (n=139) significantly differed from non-apnoeic controls in terms of age (53.9±12.8 vs. 44.9±12.8 years, p=0.002) and body mass index (BMI) (35.9±6.9 vs. 29.9±6.8 kg/m2, p<0.001). Serum 25(OH)D levels were lower in OSAS patients (17.8±7.8 vs. 23.9±12.4 ng/ml, p=0.019). In OSAS patients, levels of serum 25(OH)D were negatively correlated with sleep stage transitions (r=-0.205, p=0.028), AHI (r=-0.187, p=0.045), oxygen desaturation index (r=-0.234, p=0.011) and percentage of time with oxyhaemoglobin saturation <90% (r=-0.172, p=0.041). In contrast, they were positively correlated with average oxyhaemoglobin saturation during sleep (r=0.179, p=0.033), forced expiratory volume in 1 sec (r=0.207, p=0.037) and oxygen partial pressure (r=0.197, p=0.029). Conclusion: Vit D levels were lower in OSAS patients compared with non-apnoeic controls. Several indices of OSAS severity also correlated with Vit D levels.