In type 2 diabetes, 7 to 8 hours of sleep was linked with the fewest complications

What the researchers did

The researchers used records from a diabetes centre in Ningbo, China, between 2018 and 2023. Everyone had type 2 diabetes but none had diabetes complications when they joined.

Each person said how long they usually slept. The researchers put them into five groups, from under 7 hours to 10 hours or more.

They then tracked who developed three common diabetes complications, all caused by damage to small blood vessels: kidney disease, eye disease and nerve damage in the hands and feet.

What they found

Over the course of the study, 237 people developed at least one of the complications.

Risk was lowest for people who slept 7 to 8 hours and rose at both ends. Compared with 7 to 8 hours, sleeping under 7 hours was linked with about 70% higher risk, and sleeping 10 hours or more with nearly 90% higher risk.

The same U-shaped pattern showed up for nerve damage on its own. It held whatever people's age, weight, time spent sitting or how well they rated their sleep.

The caveats

• Sleep was self-reported, so it may not match how long people really slept.
• This kind of study can't show that sleep length caused the difference. Poor health can itself lead to very short or very long sleep.
• Everyone had type 2 diabetes and lived in one part of China, so the results may not apply to other people.
• The summary of the paper reports a clear pattern only for complications overall and for nerve damage. It doesn't say what was found for kidney or eye disease alone.

What this could mean for you

In this group, people who slept 7 to 8 hours had the fewest complications. The study can't tell us whether changing how long you sleep would lower your own risk.

If you have type 2 diabetes and regularly sleep far less than 7 hours, or 10 hours or more, it's worth mentioning to your doctor or diabetes team. Don't change any diabetes medicine without talking to them first.