Vitamin D and obstructive sleep apnea: a systematic review and meta-analysis.

Objective/background: Several studies have reported an association between 25-hydroxyvitamin D (25(OH)D) levels and obstructive sleep apnea (OSA) patients. The objective of the current study was to perform a systematic review and meta-analysis of these studies and report the findings.
Patients/methods: Authors searched for studies (through January 1, 2017) reporting 25(OH)D serum levels in OSA patients. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was followed.
Results: Fourteen studies with 4937 subjects met inclusion criteria. There were 1513 controls and 3424 OSA patients. The 25(OH)D serum levels for controls and mild OSA patients were 28.16 ± 9.39 ng/mL (95% CI 27.64, 28.68) and 27.41 ± 9.42 ng/mL (95% CI 26.87, 27.95), respectively. The 25(OH)D serum levels for controls and moderate OSA patients were 28.21 ± 9.38 ng/mL (95% CI 27.70, 28.72) and 25.48 ± 10.34 ng/mL (95% CI 24.68, 26.28), respectively. The 25(OH)D serum levels for controls and severe OSA patients were 28.32 ± 9.65 ng/mL (95% CI 27.80, 28.84) and 21.88 ± 10.24 ng/mL (95% CI 21.08, 22.68), respectively. Using random effects modeling, the 25(OH)D serum levels were decreased for patients with OSA when compared to control groups (mean differences were -2.7% for mild OSA, -10.1% for moderate OSA and -17.4% for severe OSA).
Conclusions: There was a relative insufficiency in serum 25(OH)D levels among OSA patients compared to control patients, which was incrementally exacerbated with increasing severity of sleep apnea. It was unclear whether a low 25(OH)D was a risk factor for OSA or if OSA was a risk factor for 25(OH)D. It was also possible that the association between 25(OH)D and OSA was due to body mass index (BMI).
(Published by Elsevier B.V.)