Sleep as a Medicine: How Much and How Evenly to Sleep to Live Longer

How we sleep - not just "how many hours" but also how regularly - turns out to be linked to survival. Scientific Reports published a 15-year prospective study from the Korean Ansung-Ansan cohort (9,641 people aged 40-69): long sleep >8 hours and irregular sleep patterns were associated with a higher risk of death from all causes, with the combinations "short + irregular" and "long + regular" looking the most unfavorable. There are also gender differences: men have a "riskier" short irregular sleep, women - long irregular sleep.

Background of the study

The relationship between sleep and health has long gone beyond the banal “sleep 8 hours.” According to population studies, the risk of overall and cardiovascular mortality often has a U-shaped relationship with sleep duration: both chronic sleep deficit and excessively long sleep are associated with unfavorable outcomes. But hours are only half the picture. Regularity is also important for maintaining metabolism, vascular tone, and immune balance: stable bedtimes and wake-up times synchronize circadian rhythms, while a “ragged” schedule (social jet lag, shift work, irregular weekends) upsets the internal clock and increases inflammatory and vegetative shifts.

Mechanistically, short sleep increases sympathetic activity, insulin resistance, blood pressure, and inflammation propensity – links that lead to CVD. In contrast, very long sleep often reflects low sleep efficiency or underlying diseases (depression, apnea, chronic inflammatory conditions), i.e., it can be an indicator of an existing disease and “reverse causality.” Irregularity of the regime aggravates both scenarios: with the same average number of hours, variations across days of the week are associated with worse cardiometabolic profiles, impaired lipid metabolism, and elevated C-reactive protein.

Most previous cohorts have analyzed either duration or quality surrogates, rarely considering duration x regularity combinations and their gender/age differences over time. They have often relied on single self-reports of sleep without accounting for changes over time, making it difficult to separate stable habits from transient life phases. Finally, Asian populations, where shift work and cultural patterns are common, have been underrepresented compared with European and North American cohorts.

Against this background, the value of the current study is in the long-term observation of the general population, the assessment of the combined effect of duration and regularity, and the analysis of gender/age differences in risks. Such a design helps to approach the applied formula of "healthy sleep", where it is important not only to keep the benchmark of 7-8 hours, but also to go to bed and get up at the same time, recognizing "red flags" in time - persistent short irregular sleep in men, excessively long irregular sleep in women and possible masked disorders, primarily sleep apnea.

What and how was studied

• Design: Prospective Ansung-Ansan (Korean Genome Epidemiology Study) cohort.
• Participants: 9,641 adults aged 40-69 years, without a history of heart attack/stroke at the start.
• Follow-up: median 186 months (~15.5 years); 1,095 deaths and 811 MACE (major cardiovascular events) were recorded during follow-up.
• Sleep: self-reported duration (<7 h, 7-8 h, >8 h) and regularity (regular/irregular).

Key findings

• >8 h of sleep → higher risk of all-cause mortality: adjusted HR 1.27 (95% CI 1.04-1.54) vs 7-8 h.
• Sleep x regularity combinations:
  • <7 h + irregular → HR 1.28 (1.04-1.58)
  • >8 h + regularly → HR 1.26 (1.01-1.58)
  • Comparison base - 7-8 hours + regularly.
• For MACE, there were no significant relationships after adjustments, but the trend was long + irregular for the group: HR 1.34 (0.88-2.05).

Men vs. Women: The Nuances of Risk

• Men: higher mortality at <7 h + irregular (HR 1.38; 1.06-1.80) and at >8 h + regular (HR 1.35; 1.02-1.79).
• Women: secreted >8 h + irregularly - associated with increased risk of mortality and MACE.
• Age: In 40-49 years, regular short sleep <7 h was associated with increased MACE (HR 1.46; 1.01-2.13).

How to read this in "human" language

Not only "how much you sleep", but also how predictable your routine is - an important marker of health. The risks are distributed asymmetrically: short and also "ragged" sleep affects young men, and long and irregular - more often women and older people. And yes, too much sleep can be an indicator of hidden problems (for example, apnea, chronic diseases), even if it is "regular".

Practical conclusions from the work

• Duration goal: The benchmark remains the same - 7-8 hours for most adults.
• Regularity is key: go to bed and wake up at about the same time, even on weekends.
• Red flags:
  • stable <7 h + “floating” schedule;
  • consistently >8 hours - reason to check sleep apnea and chronic conditions.
• Monitoring: If you have risk factors for CVD, look at sleep as closely as you do blood pressure and lipids.

Why could it turn out this way?

• Short sleep → sympathetic activation, insulin resistance, increased blood pressure - known links to CVD and mortality.
• Long sleep often reflects low sleep efficiency or associated illnesses; “many hours” ≠ “quality rest”.
• Irregularity disrupts circadian synchrony (metabolism, vascular tone, inflammation), enhancing the “too little” or “too much” effect.

Restrictions

• Sleep was assessed by self-report; no actimetry/polysomnography was performed.
• A one-time sleep measurement at the start - without taking into account changes over 15 years.
• Residual confounding (stress, work schedule, environment) is possible despite broad adjustments.

Conclusion

The optimal formula associated with the lowest risk of death in this cohort is 7-8 hours of sleep on a regular schedule. If your sleep is consistently shorter and irregular - or, conversely, too long - this is a reason to clean up: level out the regime, assess the presence of apnea, discuss associated factors with a doctor. Sleep is a modifiable factor, like steps or salt on the table.

Source: Park SJ et al. The impact of sleep health on cardiovascular and all-cause mortality in the general population. Scientific Reports (2025). DOI: 10.1038/s41598-025-15828-6.