From the Research
The typical sleep cycle consists of approximately 5% stage 1 (light sleep), 45-50% stage 2 (intermediate sleep), 20-25% deep sleep (stages 3 and 4, also called slow-wave sleep), and 20-25% REM sleep, as supported by the most recent study 1. These percentages vary throughout the night, with more deep sleep occurring in the first half of the night and more REM sleep in the second half. Age significantly affects these distributions, with infants spending about 50% of their sleep in REM, while elderly adults may have less than 15% REM sleep. Deep sleep also decreases with age, from about 20% in young adults to as little as 5% in older adults. The body cycles through these stages approximately every 90-110 minutes throughout the night, with 4-6 complete cycles occurring during a typical 8-hour sleep period. Some key points to consider include:
- The sleep cycle is organized into two separate states: NREM and REM sleep, with NREM sleep having four distinct stages 1.
- Normal aging carries the reduction in slow high-voltage activity (delta sleep) while REM sleep is of relatively constant duration 1.
- Disruptions to these normal percentages, whether from sleep disorders, medications, or lifestyle factors, can significantly impact sleep quality and overall health. It's worth noting that while other studies, such as 2, 3, 4, and 5, provide valuable information on sleep and insomnia, they do not directly address the question of the percentages of the stages of sleep. Therefore, the most relevant and recent study 1 is used to support the recommendation.