Is quality as important as quantity when it comes to sleep?

By Stephen Beech

Quality is just as important as quantity when it comes to healthy sleep, suggests new research.

Greater amounts of rapid eye movement (REM) and deep sleep are associated with lower risks of dozens of diseases, say scientists.

But less than five hours of total sleep per night is linked with higher risk of illness, according to the findings published in the journal PLOS Medicine.

The evidence also suggests that six to eight hours of sleep per night really is a "health safeguard" for middle-aged and older adults,

The study involving more than 95,000 British participants used wrist-worn accelerometer data to map associations between real-world sleep patterns and the incidence of more than 1,000 health conditions.

The findings showed greater REM sleep was associated with a lower risk of 83 health issues — including heart failure, dementia and Parkinson's disease.

Greater deep sleep was linked to lower risk of seven conditions, including Type 2 diabetes and major depressive disorder.

Greater sleep irregularity and wakefulness after sleep onset were each linked to higher risk of several conditions, including anxiety and substance use disorders.

The research was led by Shengzhi Sun of Capital Medical University in Beijing.

He said sleep quantity and quality is a priority of China's National Health Commission and a focus in China more broadly.

The most recent 2026 China Sleep Health White Paper found that while the average surveyed Chinese person sleeps 6.97 hours per night, 23% sleep less than six hours per night.

The same report noted that only 26% of respondents reported a consistent sleep schedule, and that disturbances to shut-eye have increased over time.

Sun says understanding how sleep patterns are linked to disease risk is therefore of great relevance.

He said: "There remains limited understanding of how sleep stages and other real-world sleep patterns relate to health outcomes.

"In part, that is because self-reported sleep measures often show poor correlation with objective assessments, making it difficult to capture real-world sleep patterns."

For the new study, researchers analyzed data from 95,559 UK Biobank participants who wore wrist accelerometers for seven consecutive days and nights.

The Chinese team used a deep-learning algorithm to calculate stages of REM, deep and light sleep, total sleep duration, wakefulness after sleep onset, and night-to-night sleep irregularity.

Participants were followed for an average of 8.9 years, and health records were available to test for associations with more than 1,000 different illnesses.

The findings also showed that there was no straightforward link between total sleep duration and the risk of many health issues.

The lowest risk concentrated in a six- to eight-hour sleep window.

People sleeping less than five hours faced the most elevated clinical vulnerability, with an increased risk of 37 conditions.

Bur Sun says, as an observational study, the research can't establish that sleep patterns directly cause disease risk.

He said: "The findings provide additional evidence supporting the role of a six to eight hours' sleep duration as a health safeguard for middle-aged and older adults, likely attributable to more favorable distributions of sleep stages.

"Maintaining a sleep duration of six to eight hours can effectively reduce the risk of multiple diseases, providing new insights for health promotion and preventive practice."

Sun added: "Sleep duration exhibited significant non-linear associations with 86 disease phenotypes, with the minimum-risk duration for the majority of these conditions, 69 phenotypes, precisely concentrated within a six- to eight-hour window."