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.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.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).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).
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