The impact of supernormal lung function on mortality risk in adults with and without sleep-disordered breathing

In the general population, supernormal lung function is associated with a lower risk of all-cause mortality.

It remains unclear whether sleep-disordered breathing (SDB) affects this relationship.

This cohort analysis included 4,839 adults. Lung function was categorised as supernormal (FEV₁ > ULN), normal (LLN ≤ FEV₁ ≤ ULN), and below normal (FEV₁ < LLN). SDB severity was classified using apnoea-hypopnoea index categories: no SDB (<5 events/hour), mild SDB (5-<15 events/hour), moderate SDB (15-<30 events/hour), and severe SDB (≥30 events/hour). The association between lung function and all-cause mortality was assessed using Cox proportional hazards models with subgroup analyses according to SDB severity and formal testing for interaction. Analyses were repeated using FVC-defined lung function groups as an alternative definition of supernormal lung function.

Among the included participants, 4,068 (84.1%) had normal lung function, 369 (7.6%) had supernormal lung function, and 402 (8.3%) had below normal lung function. During 52 421.5 person-years of follow-up (median 11.72 years; IQR, 10.46-12.56), 1,188 deaths occurred. Compared with the normal lung function group, the supernormal lung function group had a lower prevalence of baseline hypertension and cardiovascular disease. The association between lung function and all-cause mortality varied across SDB severity strata (P for interaction = 0.034). A lower mortality risk associated with supernormal lung function was observed in participants without SDB (HR: 0.24, 95% CI: 0.06-0.97), whereas this association was not statistically significant in the mild, moderate, or severe SDB strata. Below normal lung function was generally associated with an increased all-cause mortality risk. Sensitivity analyses using FVC-defined lung function groups yielded broadly consistent findings.

Supernormal lung function was associated with lower all-cause mortality primarily among individuals without SDB. These findings underscore the importance of considering SDB severity when assessing the health implications of lung function.