Serum 25(OH)D levels and obstructive sleep apnea syndrome severity in patients without comorbidities: a systematic review and meta-analysis.

Purpose: The aim of the present systematic review was to corroborate existing evidence on how serum25(OH)D levels affect obstructive sleep apnea syndrome (OSAS) severity in the absence of comorbidities.

Methods: From inception to May 2024, PubMed, Scopus, and Embase electronic databases were systematically screened to identify randomized controlled trials (RCTs), quasi-RCTs, prospective, and retrospective studies. A strict search protocol was applied following the application of PROSPERO, under the registration number CRD42023468744. The formulated question based on PICO process was: "how do serum25(OH)D levels affect the severity of OSAS or result in enhanced sleep function?". Collected results were finally reviewed for meta-analysis and quality assessment according to the ROBINS-I tool.

Results: Data from 24 studies were pooled and divided into 15 case-control studies and 9 cross-sectional studies. All studies involved a total of 2640 OSAS subjects and 933 healthy subjects. All studies underwent qualitative analysis whereas only 20 were collected for meta-analysis. Mild OSAS showed 25(OH)D levels non-statistically significant (P = 0.12) than the healthy patients whereas moderate OSAS (P = 0.004) and severe OSAS (P < 0.001) differed significantly from control groups. Meta-regression suggested that OSAS severity correlated inversely to the deficiency of 25(OH)D serum levels. Qualitative assessment and Egger's test revealed an elevated risk of bias but low presence of publication bias, respectively.

Conclusion: Serum levels of 25(OH)D were observed to be inversely proportional to OSAS severity in patients without coexisting morbidities. 25(OH)D levels in mild OSAS patients were not significantly different from non-OSAS patients, suggesting vitamin supplementation to improve potential sleep disorders.