CrossTalk opposing view: Sleep apnoea causes metabolic syndrome.

Co-morbid obstructive sleep apnoea (OSA) and metabolic syndrome (MetS) has been a focus of research since the early 1990s. Whilst it is clear that central obesity is the common factor in the aetiology of both conditions, there is good evidence that OSA, independent of obesity, partly drives the development of MetS through exacerbation of its components (central obesity, hypertriglyceridaemia, hyperglycaemia, hypertension and reduced HDL cholesterol). Indeed, the higher cardiovascular risk with this co-morbidity led to the proposal almost two decades ago of a separate syndrome (Wilcox et al. 1998). Here we provide epidemiological evidence suggesting that untreated OSA is a risk factor for MetS and/or exacerbation of MetS components. We also provide evidence showing that OSA treatment improves MetS components. Finally, we argue that MetS is a blunt measure of poor metabolic health, and that more sensitive functional measures do clearly improve when co-morbid OSA is effectively treated, thereby supporting the case for causality.