What Is a Sleep Cycle?
Sleep is not uniform but instead consists of several longer sleep cycles. The sleep cycle, also known as ultradian rhythm, is the pattern of alternating wakefulness and sleeping that the body moves through over the course of a night. Each sleep cycle is composed of three distinct stages of non-rapid eye movement (NREM) sleep and one stage of rapid eye movement (REM) sleep.
What Are the Stages of Sleep?
NREM sleep, which accounts for 75% to 80% of the total time spent in a single sleep cycle, includes three distinct stages. Stage 1, which is a transition phase between wakefulness and sleep, generally lasts between one and seven minutes. During this stage, the brain slowly becomes disengaged from its daily activities.
Stage 2 is a period of light sleep, which can last for 20 minutes or more. The person's heart rate begins to slow, their breathing becomes more regular, and they become increasingly disengaged from the external environment. Stage 3 is a period of deep sleep and restful relaxation that can last for up to 30 minutes. During this stage, the person's breathing and heart rate slow even further and their muscles become totally relaxed.
REM Sleep: What Is REM Sleep?
REM sleep, which stands for rapid eye movement sleep, is the fourth stage of the sleep cycle. During this stage, the person's eyes move rapidly from side to side and their breathing and heart rate become more irregular. REM sleep is also the period of time when dreaming occurs. It generally accounts for around 20% to 25% of the total sleep cycle, and it generally follows a period of deep sleep.
Why Do the Sleep Stages Matter?
Each sleep stage plays an important role in allowing the mind and body to recuperate from the day and prepare for a new one. The stages of sleep allow the body to engage in multiple processes including:
- Restoring physical energy
- Recharging brain activity
- Maintaining hormonal balance
- Enabling muscle growth and tissue repair
- Supporting a stable mood
- Heightening alertness
- Improving memory
- Promoting cognitive clarity
These functions all rely on a person progressing through the stages of sleep in a healthy and consistent way.
What Affects Sleep Stages?
Various factors can affect the stages of sleep. The duration of each stage will generally vary based on the person's age, their sleep patterns, alcohol consumption, or sleeping disorders. People who suffer from sleep disorders or other medical conditions typically take longer to transition in between sleep stages.
How Can You Have a Healthier Sleep Cycle?
Improving your sleep hygiene can make it easier to transition between the stages of sleep in a healthy and consistent way. Practicing these beneficial habits can help support a healthier sleep cycle:
- Maintaining a consistent sleep schedule
- Limiting alcohol use
- Exercising regularly
- Getting enough natural light exposure during the day
- Sleeping in a dark, cool, and comfortable environment
A healthy sleep cycle is composed of four separate sleep stages, including three non-rapid eye movement stages and one rapid eye movement stage. A person will typically move through four to six sleep cycles per night. These sleep stages are important in allowing the mind and body to recuperate and to support multiple functions. The duration of these stages may vary based on age, alcohol consumption, sleep patterns, and sleeping disorders. Improving sleep hygiene can help encourage healthy transitions between the sleep stages.