We read the article written by Chakhtoura et al.1 with interest. The authors reviewed potential mechanisms of bone loss and osteoporosis in patients with obstructive sleep apnea (OSA). However, the authors did not perform systematic review on all articles related to this topic. We completed a systematic review and meta-analysis of published observational studies evaluating obstructive sleep apnea and incidence of osteoporosis compared with non-apnea individuals. Reviews, case reports, letters, commentaries, abstracts, and unpublished studies were excluded. OSA was diagnosed by having polysomnography measured. Individuals who had osteoporosis at baseline were excluded.
We performed a systematic search from the Cochrane Central Register of Controlled Trials, PubMed/MEDLINE, and EMBASE databases until May 2015. We estimated the pooled risk ratio (RR) of osteoporosis comparing between OSA and non-OSA groups using a random effects model in the Review Manager 5.3 software from The Cochrane Collaboration. We also reported the pooled mean difference (MD) of a bone mineral density (BMD) measured by T-score at femur between OSA and non-OSA groups. The heterogeneity of effect size estimates across these studies was quantified using the I2 statistic and Q statistic.
A total of 9 articles underwent full-length review. Data from five cohort studies2–6 involving 113,137 participants were extracted and included in the meta-analysis. The analysis on risk of osteoporosis revealed that the pooled RR in participants with obstructive sleep apnea compared with controls was 1.37 (95 % confidence interval [CI]: 0.71–2.62, p = 0.34). The statistical between-study heterogeneity was high with an I2 of 92%. In the analysis of BMD measured by T-score at femur, the pooled MD was −0.03 (95% CI: −0.19 to 0.14, p = 0.76, I2 = 56%).
Although previous studies had demonstrated that severe OSA was associated with increased bone resorption,7 our analysis did not find a significant association of osteoporosis and OSA, or a difference in bone loss between the two groups. This may be explained by a potential mechanism that higher body weight in patients with OSA is beneficial to bone because of the positive effect of mechanical loading conferred by body weight on bone formation.8–10
A major limitation of our study was the small number of studies that met our inclusion criteria. Another limitation is that the results analyzed were from observational studies, which might be confounded by unadjusted factors such as age, gender, BMI, medication, and comorbidities, all of which might affect the risk of osteoporosis.
In conclusion, this is the first systematic review and meta-analysis of published observational studies to evaluate the association between obstructive sleep apnea and risk of having osteoporosis. Further controlled studies with adjusted effects for age, sex, or BMI are needed to accurately investigate the relationship between osteoporosis and OSA.
The authors have indicated no financial conflicts of interest.
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