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Obesity has long been recognised as the most important reversible risk factor for obstructive sleep apnoea (OSA). Analyses from the Wisconsin Sleep Cohort Study suggest that 41% of adult OSA cases, including 58% of moderate-to-severe cases, are attributable to overweight or obesity.1 As such, weight loss has long been recommended as an ancillary treatment for OSA. Longitudinal analyses from the Sleep Heart Health Study support the notion that weight loss is associated with improvements in OSA severity.2 However, the beneficial impact of weight loss was much less than the adverse effect of the same amount of weight gain in that study suggesting that the relationship between obesity and OSA is more complex than can be explained by an acute (and reversible) unidirectional causal model.
Given evidence that short sleep durations and poor quality sleep predict an increased rate of weight gain,3 ,4 many have postulated that OSA may itself predispose to obesity. Retrospective data indicate that those with recently diagnosed OSA are more likely to have had recent weight gain.5 These findings have been used to support the contention that OSA causes weight gain but of course, this may simply reflect the impact of weight gain on OSA risk. An association between OSA and elevated leptin levels, which fall with CPAP therapy, suggests that an effect of OSA on weight gain may be mediated by leptin resistance whereby improvements in leptin resistance with OSA treatment would produce weight loss.6 Uncontrolled studies have reported that initiation of CPAP therapy is associated with induction of mild weight loss.7 However, given that most patients are educated on the association between obesity and OSA at …