We’ve written before at HuffPost UK about how some people with precursors to dementia sometimes see their sleep duration lengthen years before diagnosis. 

Now, a paper published in the journal Alzheimer’s & Dementia has suggested another association may exist between rapid eye movement (REM) and early Alzheimer’s disease. 

What did the study find?

REM sleep – the last of four stages of sleep which we go through multiple times a night – is usually when we dream. 

It usually takes each cycle of sleep 90 minutes or more to complete.

The study, which involved 128 participants with mixed dementia and dementia-free status, found that people without the condition took about 98 minutes to hit REM sleep.

Those with dementia, on the other hand, appeared to take much longer (193 minutes) to reach the REM, or “dream”, stage than those without the condition.

People who took longer to get to the stage had, on average, 16% more amyloid and 29% more tau in their brains. Both of these proteins have been associated with the development of dementia. 

Co-author of the study, Dr Yue Leng, told Neuroscience News that one of the reasons this might be significant is because we consolidate our memories during REM sleep. 

“The delay in REM sleep disrupts the brain’s ability to consolidate memories by interfering with the process that contributes to learning and memory,” he said.

“If it is insufficient or delayed, it may increase the stress hormone cortisol, [which] can impair the brain’s hippocampus, a critical structure for memory consolidation.” 

What causes REM delay?

The paper says that certain medications, alcohol, sleep apnoea, and other disruptions to our natural sleep cycle can affect how quickly we reach REM. 

The study doesn’t prove that delayed REM definitely means you have dementia, though. It just shows an association.

“Future research should study the effects of certain medications that influence sleep patterns, as these may modify disease progression,” Dr Leng told Neuroscience News.

For now, though, our best bet is to stick to established dementia risk-lowering lifestyle choices, like eating well, exercising, and staying social where possible.