Sleeping too much can be just as dangerous, or even more so, than sleeping too little.
A Hungarian team published in GeroScience the largest meta-analysis to date on sleep and all-cause mortality: 79 cohort studies (46 on short sleep, 49 on long sleep), screened from 31,019 initial records. Sleeping less than 7 hours raises death risk by 14% (HR 1.14). But sleeping 9 hours or more raises it by 34% (HR 1.34), almost double.
It’s a result that contradicts the intuition that “more sleep is always better”: past a certain point, sleeping more is linked to more risk, not less.
The breakdown by sex adds another layer: in men the risk rises 16% with short sleep and 36% with long sleep, but in women it’s 14% and 44% respectively. That 44% in women with long sleep is the highest figure in the entire analysis.
The authors identified studies through PubMed, Embase and other biomedical databases, applying strict methodological quality criteria before including each cohort in the final analysis.
There’s a key nuance that can’t be overlooked: correlation isn’t causation, especially at the long sleep end. Heterogeneity between long sleep studies is very high (I squared of 92%, versus much less variability in short sleep studies), and there’s a plausible alternative explanation: reverse causation. In other words, it’s not that sleeping a lot makes people sick, it’s that people who are already sick (from an undiagnosed condition, chronic fatigue tied to an underlying issue) tend to sleep more as a consequence, not a cause.
Short sleep, on the other hand, has a much more consistent relationship across studies and well documented biological mechanisms (chronic inflammation, worse metabolic regulation, higher cardiovascular strain) that make a direct causal relationship more plausible.
This work’s impact is already showing in the scientific community: by academic citation metrics, the study is accumulating a citation rate far above what’s expected for its field in the short time it’s been published. The practical takeaway isn’t simply “sleep more,” it’s aiming for the 7 to 8 hour range, neither below it nor well above it.
Source: Ungvari Z, Fekete M, Varga P, et al. “Imbalanced sleep increases mortality risk by 14-34%: a meta-analysis.” GeroScience, 2025. DOI: 10.1007/s11357-025-01592-y.
