REM sleep vital for healthy brain, lowering dementia risk

A good night's sleep is not just about the number of hours you log.

- Mohana Ravindranath

Two particular phases of sleep in one's nightly routine seem to play outsize roles in cognitive health. ILLUSTRATION: GEORGETTE SMITH/NYTIMES

(GEORGETTE SMITH/NYTIMES)

Getting quality sleep the kind that leaves you feeling refreshed and ready for the day is also critical for a healthy brain.People with disturbed sleep, like insomnia or sleep apnoea, have a higher risk of developing dementia than those with no sleep issues.

Poor sleep can harm the brain in other ways. One study found that people in their 30s and 40s with heavily disrupted sleep such as frequent awakenings or movements were two to three times more likely to test lower in executive function, working memory and processing speeds a decade or so later.

Scientists think that deep sleep and rapid eye movement (REM) sleep are particularly influential when it comes to brain health and dementia risk.

A study published in March on people with deep sleep and REM deficiencies found that the subjects’ brains showed signs of atrophy in MRI scans 13 to 17 years after the deficiencies were observed.

The atrophy looked similar to what one would find in the early stages of Alzheimer’s disease.

When you are asleep, your brain continuously cycles through four distinct phases.

The first two stages are of lighter sleep, when your body relaxes and your heart rate and temperature drop. Then comes deep sleep or slow wave sleep, when brain activity slows; and finally REM, when you typically dream. The brain generally takes about 90 minutes to cycle through all four stages and then restarts the process.