People who want to do everything possible to prevent dementia know about the widely recognized risk factors such as high blood pressure, cardiovascular disease, diabetes and smoking.

Now: Poor sleep may also end up on that list.

Recent finding: People who spend less time in the rapid eye movement (REM) stage of sleep, when dreaming occurs, appear to be at significantly increased risk for dementia, according to a study published in Neurology.

How did this discovery come about? People with dementia are known to have sleep disturbances. But researchers wondered whether sleep problems resulted from the dementia or perhaps preceded it, pointing to an increased risk for cognitive impairment in the future.

To fully understand the scientists’ discovery, it helps to review the stages of sleep. There are five main stages—stage 1…stage 2…slow-wave sleep (stages 3 and 4 combined, also referred to as “deep sleep”)…and REM sleep. During a typical night’s sleep, we cycle from stage 1 through REM, and then begin again with stage 1. As the night progresses, time spent in REM sleep increases so that it totals about 20% of your overall sleep time. The problem is, interrupted sleep can prevent you from reaching the REM stage as often as you should.

Study details: To investigate the sleep-dementia link, researchers looked at 321 participants who were older than age 60 and who had completed an overnight sleep study called a polysomnography, which measures a person’s sleep cycles. The study participants were also under continuous surveillance for dementia through regular contact and cognitive testing.

After an average follow-up period of 12 years, researchers found that the people who developed dementia spent only 17% of their sleep time in REM sleep, on average, versus the more typical benchmark of 20%. That may not sound like a big difference, but each percentage point decrease in REM sleep was associated with about a 9% increase in dementia risk.

No one knows for sure why spending less time in REM sleep may be a predictor of dementia. Researchers did note, however, that abnormally slow or shallow breathing—red flags for sleep apnea, a sleep disorder that causes interrupted breathing throughout the night—may have contributed to these findings.

Anxiety and stress may also play a role—stressed-out individuals often experience interrupted sleep, thus reducing the time they spend in REM sleep. This is a particularly vexing problem because stress often leads to poor sleep, and poor sleep creates more stress, setting in motion a vicious cycle.

Bottom line: REM sleep appears to be protective—it may help maintain circuitry within the brain that can break down and possibly lead to dementia. More research on larger groups of people needs to be done to confirm these findings, but optimizing REM sleep by reducing stress and anxiety is a smart step to take and may help control dementia risk. Stress-reducing strategies such as yoga and meditation may help.

Also important: Be sure to see a doctor if you have any signs or symptoms of a sleep disorder such as sleep apnea. Common signs and symptoms include loud snoring…episodes of breathing cessation during sleep (witnessed by another person)…abrupt awakenings accompanied by shortness of breath…awakening with a dry mouth or sore throat…morning headache…difficulty staying asleep…excessive daytime sleepiness…attention problems…and/or irritability. Sleep disorders are treatable, and addressing them may help keep your brain healthy!