Sleeping too little or too much is a critical factor associated with long-term heart health. The Multiethnic Cohort (MEC) Study, involving over 135,000 participants, found that both short and long sleep durations were associated with a higher risk of cardiovascular disease (CVD) mortality, even after adjusting for multiple confounders. Adults should aim for 7 or more hours of sleep to maintain optimal health, as durations falling significantly outside the 7-8 hour range are linked to a higher likelihood of premature death.
The research followed participants for an average of 12.9 years, recording over 19,000 deaths. The results revealed a clear U-shaped association between self-reported sleep time and mortality risk, meaning that the risk was lowest around the 7-hour reference category and increased as sleep duration moved toward either extreme.
The U-shaped risk of sleep duration
The study identified a consistent pattern across diverse ethnic groups: the risk of death from any cause and from heart-related issues specifically follows a U-shaped curve. Participants sleeping 5 hours or less per day showed a higher risk of cardiovascular mortality compared to those in the 7-hour reference group used for the study.
Interestingly, excessive sleep was also associated with increased risk. Men and women sleeping 9 hours or more per day showed an even higher Hazard Ratio for cardiovascular death than short sleepers. While other research suggests that short sleep duration is linked to adverse inflammatory pathways, oversleeping in observational studies may be a marker of underlying health issues or fragmented sleep quality that indirectly affects the heart.
Universal risk across ethnic and lifestyle groups
One of the strengths of the MEC Study is its multiethnic population, including Japanese Americans, Native Hawaiians, African Americans, Latinos, and Whites. The U-shaped relationship between sleep and mortality held steady across all five ethnic groups, indicating that the observed association between sleep duration and health is consistent across different backgrounds.
The association remained significant even after accounting for lifestyle factors such as smoking status, physical activity levels, and body mass index (BMI). While muscular strength is crucial for longevity, the quantity of rest appears to be an important independent factor associated with cardiovascular protection.
Observed patterns in cardiovascular vs cancer mortality
A specific finding of the study was that while sleep duration was linked to cardiovascular and all-cause mortality, it did not show a significant association with cancer-related deaths in this cohort. This suggests that the physiological impact of sleep duration variances may be more closely tied to metabolic and autonomic systems than to cancer progression, though findings on this topic can vary across different studies.
Short sleep is associated with increased sympathetic nervous system activity and systemic inflammation, which can contribute to heart health issues. Long sleep, meanwhile, might reflect residual confounding or underlying frailty. The MEC study is observational and does not establish a causal mechanism, but it highlights the importance of sleep as a health marker.
Sources and related information
PMC – Sleep Duration and Mortality in the Multiethnic Cohort Study – 2013
This large prospective study of 135,000 participants investigated the link between self-reported sleep duration and mortality. The researchers found that both short (≤5h) and long (≥9h) sleep durations are associated with a higher risk of all-cause and cardiovascular mortality, but not cancer mortality. The study used 7 hours of sleep as the reference category for comparing risks.
