Can physical activity eliminate the mortality risk associated with poor sleep? A 15-year follow-up of 341,248 MJ Cohort participants.
Level 3 - non-randomized controlled study
Prospective cohort study with 15-year follow-up
PubMed 33713846 · doi:10.1016/j.jshs.2021.03.001
What was done
Prospective cohort analysis of 341,248 adults (mean age 39.7 years; 48.3% men) followed for 15 years in the MJ Cohort. Participants self-reported sleep duration (short, 6–8 h/day reference, >8 h/day) and disturbances (difficulty falling asleep, easily awakened, use of sleeping medication). Physical activity (PA) was categorized into four levels: <7.5, 7.5–14.9, 15.0–29.9, and ≥30.0 MET-h/week. Cox proportional hazards models evaluated joint associations of sleep and PA with all-cause, cardiovascular disease (CVD), and cancer mortality.
What was found
Compared with sleeping 6–8 h/day, sleeping >8 h/day was associated with higher all-cause mortality (hazard ratio [HR] 1.307, 95% CI 1.248–1.369), CVD mortality (HR 1.298, 95% CI 1.165–1.445), and cancer mortality (HR 1.128, 95% CI 1.042–1.220). Short sleep duration showed no association with mortality risk. Difficulty falling asleep increased all-cause (HR 1.120, 95% CI 1.068–1.175) and CVD mortality (HR 1.163, 95% CI 1.038–1.304). Sleeping medication use also increased all-cause (HR 1.261, 95% CI 1.159–1.372) and CVD mortality (HR 1.335, 95% CI 1.102–1.618). Long sleep duration and sleep disturbances were not associated with all-cause or CVD mortality among participants engaging in ≥15 MET-h/week of physical activity, especially those at ≥30 MET-h/week.
Why it matters
Achieving moderate-intensity physical activity of roughly 25–65 minutes per day may offset the increased mortality risks linked to long sleep duration and sleep disturbances.
Limits
Sleep parameters, sleep disturbances, medication use, and physical activity were all self-reported, creating vulnerability to recall bias and misclassification. As an observational cohort, residual confounding and reverse causation (e.g., preclinical chronic disease causing both prolonged sleep and early mortality) cannot be fully ruled out.
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