A new study has found that spending more time in rapid eye movement (REM) sleep, the stage when most dreaming occurs, may significantly lower the risk of 83 chronic diseases, including Parkinson’s disease and dementia.

The international study was led by Capital Medical University in China.

Researchers analyzed sleep data from nearly 96,000 people enrolled in the U.K. Biobank project. Using artificial intelligence algorithms, they examined one week of sleep-stage data – including REM, deep and light sleep – recorded by wrist-worn sensors. The researchers then tracked participants’ health records for an average of nine years to examine links between sleep patterns and more than 1,000 diseases.

The analysis found that every 47-minute increase in REM sleep was associated with substantial protection against 83 different diseases. People who got sufficient REM sleep had an 80% lower risk of Parkinson’s disease, a 46% lower risk of dementia and a 26% lower risk of heart failure.

The study also identified important health benefits associated with deep sleep. People who regularly got deep sleep had significantly lower risks of Type 2 diabetes and major depressive disorder. In contrast, frequent awakenings during sleep and irregular sleep schedules were associated with an increased risk of anxiety disorders.

Researchers said the optimal range for overall sleep duration appeared to be between six and eight hours per night.

People who slept less than five hours a night appeared to be the most vulnerable group, with their risk of developing 37 different diseases rising significantly, according to the researchers. The study’s lead authors said maintaining a regular six- to eight-hour sleep schedule was a vital preventive measure for adults and older people.