A new study published in the journal Alzheimer’s & Dementia has found that people who take longer to enter REM (rapid eye movement) sleep, a stage of sleep linked with dreaming and memory, could be at higher risk of developing Alzheimer’s disease and related dementias (AD/ADRD).

The study, a result of collaboration between Chinese and the US researchers, analyzed the sleep patterns and brain health of 128 older adults, including 64 participants already diagnosed with Alzheimer’s disease, 41 with mild cognitive impairment, and 23 with normal cognition. All of them were later subjected to overnight sleep studies, brain scans for amyloid beta plaques, and blood tests for Alzheimer’s-related biomarkers.

The researchers discovered a striking pattern: those who took longer to reach REM sleep tended to have more signs of Alzheimer’s disease in their brains and blood.

“Prolonged REM latency may serve as a novel marker or risk factor for AD/ADRD pathogenesis,” the study stated.

The association remained strong, even after accounting for age, gender, genetic risk factors (like APOE ε4), and other medical conditions,

According to the study, the people who took the longest to enter REM sleep not only had more amyloid beta, but also higher levels of phosphorylated tau (a toxic protein linked to brain cell death), and lower levels of BDNF, a molecule that helps protect and grow brain cells.

In simpler terms, long delays in reaching REM sleep may reflect, and possibly contribute to, brain changes seen in Alzheimer’s disease.

Interestingly, the study also looked at slow-wave sleep, another important sleep stage, and found no link between it and Alzheimer’s biomarkers. “Slow-wave sleep was not associated with AD/ADRD biomarkers,” the authors noted.

The researchers call for further trials to test if improving REM sleep could lower dementia risk:

“An intervention trial is needed to determine if targeting REML can modify AD/ADRD risk.”

This is not the first time scientists have suspected a connection between poor sleep and Alzheimer’s. However, this study uses multiple biomarkers, including brain scans and blood tests, while carefully adjusting for confounding factors. The findings are expected to help doctors identify at-risk individuals earlier, long before symptoms appear.

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