Many people believe that the longer we sleep, the better it is for our bodies. However, recent research suggests that sleeping too little or too much may both be linked to health risks.
On September 19, 2026, the international journal npj Aging published a study that followed 18,282 people for about nine years to examine the link between sleep duration and age-related physical decline.
The results showed that not only people who slept less than seven hours, but also those who slept more than nine hours, had a stronger association with frailty, a state of physical weakening.
In this article, we draw on this large follow-up study to look at how much sleep may support healthy aging.
Why the Link Between Sleep and Health Is Drawing Attention
Sleep is involved in many bodily functions, not only recovery from mental and physical fatigue, but also organizing memories, immune function, hormone release, and regulating metabolism.
Chronic lack of sleep is known to be linked not only to poor concentration and fatigue during the day, but also to health risks such as lifestyle-related diseases.
On the other hand, sleeping longer does not necessarily mean better health.
Past epidemiological studies have reported that the relationship between sleep duration and health risk can follow a U-shaped curve, with higher risk for both short and long sleep.
However, it is still not fully understood whether long sleep itself harms health, or whether declining health leads people to sleep longer.
This study examined the link between sleep and health from the perspective of age-related physical decline.
A New Study Following About 18,000 People for About Nine Years
The study, published in September 2026, used data from the China Health and Retirement Longitudinal Study, a large-scale health survey in China.
The participants were 18,282 men and women aged 45 and over, with a median follow-up period of 8.9 years.
The research team divided participants’ self-reported sleep duration into three groups, less than 7 hours, 7 to 9 hours, and more than 9 hours, and analyzed their association with frailty.
Frailty refers to a decline in muscle strength, stamina, and mental and physical vitality with age, which makes people more likely to fall ill, have falls, or come to need care.
In this study, frailty was assessed using an index combining 44 health-related items.
During the follow-up period, the number of people newly identified as frail was 2,125 (11.6% of the total).
The research team statistically examined how differences in sleep duration related to the onset of frailty.
Is the Risk Higher When Sleep Is Too Short or Too Long? The Results
The analysis found that, compared with people who slept 7 to 9 hours, both shorter and longer sleepers showed an association with frailty.
Specifically, using the 7-to-9-hour group as the reference, the results were as follows:
- Less than 7 hours: about 2.05 times the odds of frailty
- More than 9 hours: about 1.45 times the odds of frailty
Odds here are not the same as the probability of becoming frail. So this does not mean that people who sleep less than seven hours are twice as likely to become frail.
In addition, when sleep duration was analyzed as a continuous value, the odds of frailty showed a U-shaped relationship, and the lowest point was at about 7.1 hours.
The research team suggests that, among the people studied, about 7 to 8 hours may be a relatively favorable range of sleep.
However, this does not mean that sleeping 7.1 hours will prevent frailty.
That is because this was an observational study, and it did not directly prove a cause-and-effect link between sleep duration and frailty.
We also need to keep in mind that sleep duration was self-reported, and that factors such as health status may have influenced the results.
Why Is Long Sleep Also Linked to Health Risks?
While it is easy to imagine how lack of sleep affects health, some people may wonder why long sleep is linked to health risks too.
Several possible explanations have been suggested for the link between long sleep and declining health.
For example, chronic illness, lower physical activity, symptoms of depression, and poorer sleep quality may all be related to longer sleep.
It is also possible that when people do not get enough rest, for example because they wake up many times during the night, they end up sleeping or staying in bed longer.
In other words, sleeping longer does not necessarily harm health directly; it may be that physical problems are reflected in how long we sleep.
What matters is not to judge your health by the number of hours you sleep alone.
In fact, the Sleep Guide for Health Promotion 2023 from Japan’s Ministry of Health, Labour and Welfare starts from the premise that sleep needs vary from person to person, and places importance on the sense of feeling rested after sleep.
Sleep Habits That Support Healthy Aging
In this study, about seven hours was linked to the best results, but the amount of sleep we need varies with age, constitution, and lifestyle.
For adults, the Ministry of Health, Labour and Welfare recommends getting the sleep you need, with six hours or more as a guide, while taking individual differences into account.
For older adults, considering the health risks of spending long hours in bed, it suggests aiming for no more than eight hours in bed. Note, however, that time in bed and actual sleep time are not the same.
In daily life, it is important to look not only at how long you sleep, but also at whether you feel well rested in the morning, whether you feel very sleepy during the day, and whether your daily rhythm is stable.
Waking up at about the same time every morning, getting moderate physical activity during the day, and avoiding bright light before bed can also lead to good sleep habits.
If you still feel very sleepy or tired even after sleeping enough, there may be an underlying sleep disorder, so it is a good idea to consult a medical professional.
What this study shows is not simply that longer sleep is better, but the importance of getting the sleep you need while also getting good-quality rest.
To age in good health, let’s not get caught up in the numbers alone, and instead pay attention to how we sleep each day.