Longer Sleep Linked to Kidney Disease Risk in Type 2 Diabetes

The research is a prospective cohort study, a type of observational study in people. It followed 678 Japanese outpatients with type 2 diabetes for an average of 6.0 years (give or take 2.7 years). It was published in 2026 in the Journal of the Endocrine Society. Observational studies can find links. They cannot show that one thing causes another.

The researchers looked at diabetic nephropathy, also called diabetic kidney disease. This is kidney damage caused by long-term diabetes. They counted either new cases or worsening of existing disease as a single combined outcome. During follow-up, 215 of the 678 participants reached that outcome.

The team recorded lifestyle habits at the start, and again at year 2 and/or year 5. They averaged each person's measurements up to the point of the outcome or the end of follow-up. Of all the lifestyle factors they examined, average sleep duration was the only one linked to the outcome.

The direction mattered. The authors conclude that longer sleep, but not shorter sleep, was associated with a higher risk. The trend held after adjusting for key lifestyle and diabetes-related factors. The link was stronger in older participants and in those who already had microalbuminuria (small amounts of protein in the urine, an early sign of kidney damage) or reduced kidney function.

It does not give the sleep-hour categories or the size of the risk, so we cannot report them.

The authors do not claim long sleep harms the kidneys. In a statement released by the Endocrine Society, study author Tomoya Mita of Juntendo University in Tokyo said longer sleep "may be a readily observable marker of underlying health vulnerability." He also said people should not read the findings as advice to sleep less, because "we cannot establish a causal relationship." The Endocrine Society release also states that diabetic kidney disease affects about 30% to 40% of people with diabetes.

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What does this mean for personal health? The study did not test sudden changes in sleep. It looked at average sleep over years. Mita said longer sleep may be a useful clue to identify people with diabetes who may need closer attention to their kidney health. Beyond that, any advice here is our editorial suggestion, not a finding of the study: if someone notices a clear, lasting increase in how long they sleep, it may be worth mentioning to a clinician. It may be most relevant to older adults with diabetes and to people whose kidney tests already show early changes.

There are limits. All participants were Japanese outpatients with type 2 diabetes, so the results may not apply to other groups.

This differs from the REM sleep study we covered on October 6, which tracked sleep stages and disease risk in nearly 96,000 UK adults. That was a different study with a different design. This one adds that sleep length alone may carry information in a specific group, though both are observational.

Next, watch for studies that measure sleep objectively and track changes over time. They could show whether longer sleep helps flag kidney risk in routine diabetes care.

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