Abstract
STUDY OBJECTIVES: A recent study reported an association between obstructive sleep apnea (OSA) and low vitamin D levels. In this study, we measured vitamin D levels in patients referred for evaluation of suspected OSA and sought to identify associated risk factors for vitamin D deficiency. Our objective was to determine whether evaluations of patients with suspected OSA should include routine screening for vitamin D deficiency. METHODS: Using a cross-sectional study design, we measured vitamin D levels in consecutively enrolled patients referred for an OSA evaluation to Dr. Lutfi Kirdar Kartal Training and Research Hospital in Istanbul, Turkey. We conducted full-night polysomnography and compared vitamin D levels both between patients with OSA and patients without OSA and across the various severity levels of OSA. We evaluated the association between vitamin D levels and various clinical and demographic characteristics, including the apnea-hypopnea index and body mass index. RESULTS: From April 2014 to June 2015, 195 patients were referred for OSA evaluation. Of these, 181 patients (93%) consented to participate and underwent full polysomnography and measurement of vitamin D levels. The mean ± standard deviation age was 49 ± 12 years and body mass index of 31 ± 6 kg/m(2). Polysomnography led to the diagnosis of OSA in 162 of the patients (89.5%): 52 (32%) were categorized as having mild OSA, 38 (23.5%) as having moderate OSA, and 72 (44.5%) as having severe OSA. Vitamin D level was 15.5 ± 11.6 ng/mL (95% confidence interval; 13-17 ng/mL) and 134 patients (74%) met the criterion for vitamin D deficiency (< 20 ng/mL). Sex, vitamin D levels, and percentage of patients with vitamin D deficiency were similar in patients with and without OSA (P > .05). Vitamin D levels were similar across OSA severity categories (P = .68). We found no association between vitamin D levels and the apnea-hypopnea index or body mass index. CONCLUSION: A large proportion of patients referred for OSA evaluation had vitamin D deficiency. Vitamin D levels did not differ by OSA diagnosis status or severity. Patients referred for polysomnography should undergo routine screening for vitamin D deficiency as well as clinically indicated treatment to prevent associated comorbidities.