Sleeping Over 8 Hours Increases Death Risk, Korean Study Finds

Research tracking 9,000 adults shows irregular sleep patterns and prolonged sleep duration linked to higher mortality, with different risks for men and women

A 15-year Korean study following over 9,000 adults has found that sleeping more than eight hours per night significantly increases mortality risk, particularly when combined with irregular sleep patterns. Published in Scientific Reports, the research from Hanyang University Medical Center reveals that maintaining consistent sleep of seven to eight hours offers the best protection against early death.

The comprehensive study tracked participants from both rural and urban communities in Korea, recording 1,095 deaths and 811 major cardiovascular events during the follow-up period. Researchers discovered that people sleeping more than eight hours faced notably higher mortality risks compared to those getting seven to eight hours nightly.

Sleep regularity emerged as a crucial factor alongside duration. Participants with irregular sleep patterns showed increased mortality risk, though the effect varied by gender. Men with less than seven hours of irregular sleep or more than eight hours of regular sleep faced the highest risks. Women showed different patterns, with the greatest danger coming from more than eight hours of irregular sleep.

The research categorized participants into groups based on self-reported sleep duration (less than seven hours, seven to eight hours, or more than eight hours) and sleep regularity (regular or irregular). This approach allowed researchers to examine how different combinations affected health outcomes.

Mortality Risk by Sleep Pattern

Sleep Pattern	Men	Women
<7 hours irregular	Highest risk	Moderate risk
7-8 hours regular	Lowest risk	Lowest risk
>8 hours regular	High risk	Moderate risk
>8 hours irregular	Moderate risk	Highest risk

The findings challenge common assumptions about sleep and health. While many people believe more sleep is always better, the study suggests otherwise. Prolonged sleep may indicate underlying health problems like undiagnosed sleep apnea or other conditions that increase mortality risk.

Short sleep duration, while not reaching statistical significance for increased mortality, showed concerning trends. Sleep deprivation is known to increase risks for hypertension, diabetes, and obesity, which may explain the observed patterns.

Age played a significant role in sleep-related health risks. Middle-aged individuals between 40 and 49 years showed greater vulnerability to short sleep duration effects. Adults over 60 faced higher risks from prolonged sleep, suggesting age-specific sleep recommendations may be necessary.

The sex differences observed in the study likely stem from various biological and social factors. Hormonal differences affect sleep regulation differently in men and women. Women often face additional sleep disruptions from caregiving responsibilities and hormonal transitions. Men may experience more work-related stress and have higher rates of sleep apnea.

Interestingly, the study found no significant direct link between sleep patterns and cardiovascular events after adjusting for other factors. However, trends suggested that people with long, irregular sleep might face increased cardiovascular risks.

The research builds on growing evidence that sleep regularity matters as much as duration. Previous studies focused primarily on how many hours people slept, but this work shows that consistency in sleep-wake timing plays an equally important role in health outcomes.

Sleep serves essential functions including physical restoration, memory consolidation, and metabolic regulation. Disruptions to either duration or regularity can interfere with these processes, potentially explaining the increased mortality risks.

The findings have important implications for public health recommendations. Current guidelines often emphasize getting enough sleep without addressing regularity. This research suggests both factors deserve equal attention in sleep health interventions.

Healthcare providers may need to reconsider how they assess and advise patients about sleep. Simply asking about hours slept misses the critical dimension of sleep regularity. Screening for both aspects could help identify individuals at higher risk for adverse health outcomes.

The study's large sample size and long follow-up period strengthen its findings. However, reliance on self-reported sleep data represents a limitation, as people may not accurately recall their sleep patterns.

For individuals concerned about their sleep health, the message is clear: aim for seven to eight hours of sleep with consistent bed and wake times. Deviations in either direction, whether too little or too much sleep, appear to carry health risks.

Future research should investigate the mechanisms linking prolonged sleep to increased mortality. Understanding whether extended sleep causes health problems or merely reflects existing conditions could inform more targeted interventions.

The study emphasizes that optimal sleep health requires balance. Neither extreme of sleep duration appears beneficial, and maintaining regular patterns matters as much as getting the right amount. As sleep science advances, personalized recommendations based on age, sex, and individual health factors may replace one-size-fits-all guidelines.