A study published on April 22, 2026, in Neurology^® found that people with focal epilepsy—seizures that start in one part of the brain—who get poor sleep have a higher risk of developing dementia than people without focal epilepsy.

The study compared dementia rates among people with focal epilepsy, people with a history of stroke, and people with neither condition and whether they got optimal or poor sleep. The researchers found that poor sleep was linked to a higher risk of dementia in all three groups, but the difference was greatest among people with focal epilepsy.

Getting optimal sleep was also linked to better thinking skills, especially in people with focal epilepsy. In this study, optimal sleep means sleeping six to eight hours a day. Sleeping less than six hours or more than eight hours was considered poor sleep.

Researchers studied more than 482,000 adults with an average age of 58 who did not have dementia at the start of the study. About 3,800 participants had epilepsy and 6,300 participants had a history of stroke. The remaining participants didn’t have epilepsy or a history of stroke.

Participants were followed for an average of 12 years. They reported how many hours they slept per night, and they completed cognitive tests that measured their ability to plan, problem-solve, and make decisions.

Across all groups, people with optimal sleep had better cognitive test scores. However, the benefits of optimal sleep were strongest in people with focal epilepsy. Dementia also developed more often in people with poor sleep. Among participants with epilepsy, two percent of those who had optimal sleep developed dementia, compared to five percent of those who had poor sleep.

For people who did not have epilepsy, one percent with optimal sleep developed dementia compared to two percent of people who had poor sleep.

After accounting for factors such as age, education, and socioeconomic status, the researchers found that people with epilepsy and poor sleep had about five times the risk of developing dementia compared to people without epilepsy who had optimal sleep.

“Improving sleep may offer an effective and affordable management strategy to lower dementia risk in people with focal epilepsy,” said study author Xin You Tai, DPhil, of the University of Oxford in the United Kingdom.

The researchers note that the study shows an association but does not prove that poor sleep causes dementia. One limitation is that sleep duration was self-reported rather than measured directly.

Key Takeaways

• In this study, poor sleep is linked to higher dementia risk in people with focal epilepsy compared to people without epilepsy.
• Participants who slept six to eight hours a night had better thinking skills in both people with and without focal epilepsy.
• This study does not prove that poor sleep causes dementia.