Sleep apnoea tied to lower fitness and higher mortality

Sleep quality and physical fitness are known to travel together, and each has separately been linked to how long people live. Obstructive sleep apnoea fragments sleep and drops blood oxygen repeatedly through the night, which could plausibly blunt daytime exercise capacity. If that reduced capacity were the route by which sleep apnoea shortens life, then improving fitness might be a lever worth pulling. Testing that idea requires measuring sleep objectively and fitness objectively in the same people, then following them for years — which is rarely done outside sleep clinics.

The analysis used 1001 participants from the population-based SHIP-TREND cohort, recruited between 2008 and 2012, who each completed a single night of polysomnography and a symptom-limited cardiopulmonary exercise test. Mean age was 54, with a range of 44-63 years, and 47.1% were women. Sleep was characterised by the apnoea-hypopnoea index and the oxygen desaturation index; fitness was captured as peak oxygen uptake. Multivariable linear regression related sleep to exercise measures, Cox regression related both to all-cause mortality, and a mediation analysis tested whether reduced exercise capacity carried the effect of impaired sleep on death.

The apnoea-hypopnoea index was 4.9 events per hour overall and higher in men (7.9) than women (2.6; p<0.001), while peak oxygen uptake was lower in women (22 mL·min-1·kg-1) than men (27 mL·min-1·kg-1; p<0.001). Both a higher apnoea-hypopnoea index and a higher oxygen desaturation index were inversely associated with peak oxygen uptake. Over a median 10.3 years of follow-up there were 73 deaths, and the apnoea-hypopnoea index was significantly associated with all-cause mortality across models, with hazard ratios ranging from 1.31 to 1.72. Crucially, the mediation analysis showed a significant direct effect but an indirect effect through peak oxygen uptake that was not statistically significant.

This confirms in a general-population sample what clinic-based studies have suggested, that sleep-disordered breathing tracks with poorer measured exercise capacity and higher mortality. It complicates the tidier story that low fitness is the mechanism: the direct path from apnoea severity to death survived adjustment while the fitness pathway did not reach significance, though with 73 deaths the mediation test had limited power to detect a partial effect. Open questions include whether treating apnoea raises peak oxygen uptake, whether the sex difference in apnoea severity alters risk, and what a single night of monitoring misses.

This is a reason to think that snoring with witnessed pauses and unrefreshing sleep is worth taking seriously as a health signal rather than a nuisance, particularly in middle-aged men, where the index was markedly higher. It also suggests that if your measured exercise capacity seems lower than expected for your training, sleep-disordered breathing is one plausible contributor among many. What the study does not show is that pushing fitness up would neutralise the risk, because the fitness pathway to mortality was not statistically supported here. Observational data of this kind describes patterns, not causes.