Occupational
Mediating role of biological aging in the relationship between long working hours, poor sleep quality, and mortality in the U.S. working population Xiang Li* Xiang Li Li Li Li Li University of California Los Angeles
Long working hours (LWH) and poor sleep quality (PSQ) are each associated with increased mortality risk, yet their joint effects remain understudied. Biological age, a composite biomarker-based measure of biological aging, has been increasingly evaluated in chronic disease research, but its role as a potential pathway linking work- and sleep-related exposures to mortality among workers has rarely been examined. We analyzed a nationally representative sample of 13,491 employed adults (aged 18-85 years) from the U.S. National Health and Nutrition Examination Survey (NHANES 2005–2014), with mortality follow-up through 2019 via linkage to the National Death Index. LWH was defined as working ≥55 hours per week, and PSQ as having one or more adverse sleep characteristics (diagnosed sleep disorder, self-reported trouble sleeping, or sleep duration <7 or >9 hours). Biological age was estimated using the PhenoAge algorithm based on 11 clinical biomarkers. Causal mediation analysis using G-Computation was applied to estimate the total effect (TE) of joint exposure to LWH and PSQ on all-cause mortality, as well as the total indirect effect (TIE) mediated through biological age; effects were reported as marginal RRs with 95% CIs. Models adjusted for age, sex, race and ethnicity, income, education, marital status, and baseline cardiometabolic conditions (diabetes, hypertension, or cardiovascular disease). During a mean follow-up of 9.85 years, 344 deaths were observed. Compared with workers with neither LWH nor PSQ, those exposed to LWH and PSQ had higher all-cause mortality (TE RR = 1.47, 95% CI: 1.42-1.53). The indirect pathway through biological aging was small in magnitude (TIE RR = 1.03, 95% CI: 0.99-1.07), accounting for approximately 13% of the total effect. These findings suggest that co-occurring long working hours and poor sleep quality are associated with elevated mortality risk among U.S. workers, with biological aging contributing slightly to this association.