Obstructive sleep apnea may increase the risk of dementia in older adults, especially women

A common but often underdiagnosed sleep disorder contributes to dementia in adults — especially women, a Michigan Medicine study finds.

Researchers found this by analyzing survey and cognitive test data from more than 18,500 adults to determine the potential impact of known or suspected obstructive sleep apnea on the risk of developing dementia.

Obstructive sleep apnea is a chronic sleep disorder characterized by episodes of interrupted or restricted breathing during sleep.

Impact on dementia risk

For all adults aged 50 and older, having known obstructive sleep apnea or symptoms of it — which people often don’t know about — was associated with an increased risk of having signs or being diagnosed with dementia in the future. Although the overall rate of dementia diagnoses was less than 5%, the association remained statistically significant even after accounting for other factors such as race and education level.

Across all age groups, women with known or suspected sleep apnea were more likely to be diagnosed with dementia than men. In fact, the rate of dementia diagnoses among men decreased, while among women it increased with age.

The results are published in the journal Sleep Advances.

"Our findings provide new insights into the role of treatable sleep disorders on long-term cognitive health at the population level for both women and men," said senior author Tiffany J. Braley, M.D., M.S., a neurologist and director of the Division of Multiple Sclerosis and Neuroimmunology at the University of Michigan.

The reasons for the sex difference in dementia diagnoses based on sleep apnea status are not yet known. However, researchers have suggested several possible explanations. Women with moderate sleep apnea may have a higher risk of cardiovascular disease and are more likely to suffer from insomnia, which can negatively impact cognitive function.

"Estrogen begins to decline as women enter menopause, which can impact their brains," added co-author Gali Levy Dunyetz, Ph.D., M.P.H., assistant professor of neurology and the division of sleep medicine at the University of Michigan. "During this time, they become more susceptible to changes in memory, sleep, and mood, which can lead to cognitive decline. Sleep apnea increases significantly after menopause but remains underdiagnosed. We need more epidemiological studies to better understand how sleep disorders in women affect their cognitive health."

Six million Americans are officially diagnosed with sleep apnea, but the disorder is believed to affect nearly 30 million people.

In a 2024 report, the Lancet Commission identified several modifiable risk factors that together account for about 40% of global dementia cases. Although sleep was not included in the formal risk factors, the commission noted that sleep apnoea "may be associated with dementia" and suggested considering adding questions on dementia for people with the disorder.

Other modifiable risk factors for dementia include cardiovascular disease and mental health problems, which can be worsened by untreated sleep apnea.

"These potential harms caused by sleep apnea, many of which threaten cognitive function and decline, highlight the importance of early diagnosis and treatment," Brayley said. "Obstructive sleep apnea and the sleep deficit and fragmentation it causes are also associated with inflammatory changes in the brain that may contribute to cognitive impairment."

The Michigan Medicine study used existing data from the Health and Retirement Study, an ongoing survey that represents Americans ages 50 and older.

"This study design cannot definitively prove that sleep apnea causes dementia—that would likely require a randomized trial over many years to compare the effects of sleep apnea treatment with no treatment," said co-author Ronald D. Chervin, M.D., M.S., director of the Division of Sleep Medicine in the Department of Neurology at the University of Michigan.

"Because such a trial may be a long time, if ever, away, reversal studies like ours in large databases may be among the most informative for years to come. In the meantime, the results provide new evidence that clinicians and patients should consider the possibility that untreated sleep apnea causes or worsens dementia when making decisions about sleep apnea testing and treatment."