In a study of 409,000 adults, one everyday habit seemed to offset some of the brain effects of diabetes, heart disease and stroke
Type 2 diabetes, heart disease and stroke are among the best-known risk factors for memory decline and dementia. Researchers at Karolinska Institutet in Sweden wanted to know whether anything in daily life could soften that link. They analyzed data from 408,977 middle-aged and older adults in the UK Biobank, more than 54,000 of whom had at least one of these conditions, along with brain scans for nearly 35,000. They compared cognitive tests and brain size across people with different habits.
The habit that stood out was sleep. Among people with type 2 diabetes, heart disease or stroke, those with a healthy sleep pattern did better on tests of general thinking, problem-solving and processing speed than people with the same conditions who slept poorly. They also had larger total brain volume and more gray and white matter.
The link between sleep and brain structure was stronger in people with these conditions than in people without them, which suggests good sleep may matter most for those whose brains are already under strain.
“Cardiometabolic diseases are very common in older adults, and they are among the most well-established risk factors for declining cognitive and brain health,” said Abigail Dove, a researcher at the Aging Research Center at Karolinska Institutet. “Our findings suggest that healthy sleep may help offset some of the adverse consequences of cardiometabolic disease for the brain. This is meaningful because for most people, improving sleep is an accessible and achievable goal.”
Sleep was scored on five self-reported factors: how long people slept, whether they were morning or evening types, whether they had insomnia, whether they snored, and how sleepy they felt during the day. People were grouped as having a healthy, intermediate or poor sleep pattern.
The differences were modest. In the cognitive tests, people with good sleep performed slightly better, not dramatically better, and the brain volume differences were measured in fractions of a standard deviation. But across tens of thousands of people, the pattern was consistent.
Why might sleep help? Diabetes, heart disease and stroke can damage small blood vessels in the brain and increase inflammation. Sleep is when the brain clears waste products and repairs itself, and poor sleep has been linked to high blood pressure, higher blood sugar and inflammation, the same processes that harm the brain in these conditions.
The second finding is about which parts of sleep matter. The score combined five habits, so no single factor explains the result. Snoring, for example, can be a sign of sleep apnea, which is common in people with heart disease and diabetes and is treatable. Sleep keeps showing up in research on the aging brain, from frequent daytime napping to how much daylight people get, and even what time people go to bed.
For people living with diabetes, heart disease or a past stroke, the practical takeaway is that sleep is worth treating as part of their care. Regular sleep and wake times, getting snoring or daytime sleepiness checked for sleep apnea, and talking to a doctor about persistent insomnia are reasonable steps that carry little risk.
There are limits to what this shows. The study is observational, so it cannot prove that better sleep protects the brain; people whose brains are healthier may also sleep better. Sleep was self-reported, the cognitive tests were shorter than a full clinical assessment, and UK Biobank participants tend to be healthier and wealthier than the general population.
Source
Miao Y, Fingerson L, Walters E, et al. “Healthy Sleep Mitigates the Association Between Cardiometabolic Disease and Poorer Cognitive and Brain Health.” Journal of the American Heart Association, 2026.
DOI: 10.1161/JAHA.126.051940
