Study links chronic insomnia to higher dementia risk, researchers say

A US study published in the journal Neurology found that people with chronic insomnia face a 40% higher risk of developing mild cognitive impairment or dementia than those without the sleep disorder, researchers said.

The longitudinal study tracked 2,750 cognitively healthy adults with an average age of 70 for just over five years. Chronic insomnia was defined as having trouble sleeping at least three days a week for three months. At the start of the study, 440 participants had a diagnosis of chronic insomnia.

During follow-up, 14% of participants with chronic insomnia developed mild cognitive impairment or dementia, compared with 10% of those without an insomnia diagnosis. After accounting for age, blood pressure, use of sleep medications and a diagnosis of sleep apnea, the researchers reported that the association persisted, representing what they described as the equivalent of roughly three-and-a-half years of accelerated brain ageing.

Participants completed annual memory and thinking tests and underwent brain imaging to assess markers associated with neurodegeneration. Those with chronic insomnia showed faster declines on cognitive tests and evidence of greater brain pathology, including increased white matter hyperintensities—areas of small vessel damage—and greater amyloid plaque accumulation, a protein linked to Alzheimer’s disease. The pattern of changes in some insomnia sufferers resembled those seen in people carrying the APOE ε4 gene, a well-established genetic risk factor for Alzheimer’s; APOE ε4 carriers in the study exhibited steeper cognitive declines.

"Insomnia doesn't just affect how you feel the next day—it may also impact your brain health over time," said Dr. Diego Carvalho, a neurologist and sleep medicine expert at the American Academy of Neurology. He said the results suggest chronic insomnia could be an early warning sign or contribute to later cognitive problems, and that effects may involve both amyloid-related processes and small-vessel disease.

The researchers cautioned that the study has limitations. Insomnia diagnoses were identified through medical records rather than standardized, study-administered sleep assessments, and the analysis could not account for undiagnosed cases of insomnia. The observational design also cannot prove a direct cause-and-effect relationship between insomnia and dementia.

The findings add to mounting evidence that poor sleep is associated with a range of adverse health outcomes, including stroke, certain cancers and neurodegenerative disorders. Previous research has estimated that about one in six people in the United Kingdom suffers from insomnia, and roughly two-thirds of them do not seek help. Current estimates place the number of people living with dementia in the UK at about 944,000, with projections by University College London suggesting that figure could rise to 1.7 million within two decades as populations age. In the United States, the number of people with dementia is estimated at close to 7 million.

Researchers and clinicians said the results underscore the importance of identifying and treating chronic insomnia. They noted that treatments such as cognitive behavioral therapy for insomnia are effective for many patients and may have downstream benefits for brain health. The study’s authors called for further research with standardized sleep assessments and interventional trials to determine whether treating insomnia can slow cognitive decline.

Separately, researchers at University College London are conducting a large trial of blood tests designed to detect proteins linked to Alzheimer’s disease in hopes of improving early diagnosis in health systems such as the NHS. While there is currently no cure for Alzheimer’s, earlier detection could affect clinical care and recruitment into treatment trials.

Clinicians said the new findings are another reminder that sleep health is a potentially modifiable factor in healthy ageing, but they emphasized the need for additional studies to establish whether improving sleep can reduce the risk of dementia.