Sleeping too much may significantly increase the risk of death from chronic kidney disease (CKD), a Japanese research team warns.

The researchers suggest that prolonged sleep may alter hormones related to kidney health or reflect underlying health problems and access to health care.

CKD is a long-term condition that occurs when the kidneys are no longer able to filter waste from the blood effectively. According to the US Centers for Disease Control and Prevention (CDC), about 35.5 million adults in the US have the disease, but nine out of 10 are unaware they have it.

"This study highlights the importance of understanding how both too little and too much sleep can affect kidney health," said Shuai Guo, a public health researcher at the University of Tsukuba in Japan.

He said the study results suggest that prolonged sleep may be a sign of underlying health problems that contribute to an increased risk of death from chronic kidney disease, especially in younger people.

For the study, Guo and colleagues recruited more than 95,000 Japanese adults aged 40–79 and followed them for nearly 19 years.

Participants were asked to report their sleep time each night and were divided into groups according to sleep duration: less than 6 hours, 6–7 hours, 7–8 hours, 8–9 hours, and more than 9 hours.

The CDC recommends that adults get at least 7 hours of sleep per night. For people aged 61–64, the maximum is 9 hours, and those over 65 should get no more than 8 hours per night.

The study found that sleeping 8–9 hours a night was associated with a 41% increased risk of death from chronic kidney disease compared with those who slept 7–8 hours. The risk increased to 82% for those who slept 9 hours or more a night.

Notably, the risk was higher in people under 65, the researchers said.

Although more research is needed to clarify the link between sleep and the risk of chronic kidney disease, the researchers have several hypotheses, including:

Sleeping too much may alter levels of cortisol and melatonin, two hormones that affect kidney function.

Sleeping too much may increase levels of a protein that causes “progressive renal fibrosis,” a buildup of scar tissue in the kidneys that is often associated with the end stages of chronic kidney disease.

Obstructive sleep apnea (OSA), a risk factor for and progression of chronic kidney disease, is more common in people who sleep too much.

Long sleep duration is also associated with a higher risk of cardiovascular problems, which can lead to impaired kidney function.

Long sleep duration may reflect low socioeconomic status. People with low socioeconomic status often have poorer access to or receive poorer health care, increasing their risk of chronic kidney disease.

This study highlights the importance of maintaining healthy sleep habits. Getting enough sleep, not too little or too much, not only helps promote overall health, but also plays an important role in protecting the kidneys and reducing the risk of death.

Experts recommend that adults maintain 7–8 hours of sleep per night and be aware of potential health problems if their sleep duration is unusually long.