Objective rest-activity rhythm amplitude and lung function in US adults: A cross-sectional analysis of the 2011-2012 National Health and Nutrition Examination Survey.

This cross-sectional analysis of 4,150 US adults from the 2011-2012 NHANES examined associations between wrist-accelerometry-derived rest-activity rhythm metrics and respiratory outcomes spanning spirometry, exhaled nitric oxide, and self-reported respiratory symptoms and diagnoses. Relative amplitude (RA), interdaily stability, intradaily variability, M10, L5, and cosinor parameters were derived from hourly monitor-independent movement summary (MIMS) values. The co-primary outcomes were FEV1 and FVC z-scores (GLI 2012); secondary outcomes included FEV1/FVC, FeNO, and latent-class-derived respiratory phenotypes. Survey-weighted linear regression with progressive adjustment for demographics, socioeconomic factors, BMI, smoking, depression, and wear time was employed, with activity volume (M10 and total daily activity) addressed in dedicated sensitivity models. Each 1-SD increase in RA was associated with a 0.108 higher FEV1 z-score (95% CI: 0.053-0.164; p < 0.001), with concordant signals for cosinor amplitude and M10. Each 1-SD increase in RA was also associated with a 0.120 higher FVC z-score (95% CI: 0.073-0.166; p < 0.001), a magnitude comparable to that for FEV1. This association persisted in never-smokers, those without diagnosed respiratory disease, and after adjusting for total activity volume. No amplitude metric was associated with FEV1/FVC or FeNO. Rhythm metrics did not independently distinguish respiratory phenotypes after full covariate adjustment. In conclusion, a stronger day-night activity contrast was associated with higher FEV1 and FVC z-scores, but not with FEV1/FVC, FeNO or adjusted respiratory phenotype membership, and this association was not attenuated by adjustment for M10 or total daily activity volume. Prospective studies with repeated accelerometry and post-bronchodilator spirometry are required to determine whether the day-night activity contrast has predictive value for lung-function decline.