For many people, sleep feels like a reprieve from the busyness of waking hours, but while our consciousness quiets during slumber, our body and brain are working hard to restore, regulate, and grow vital functions. Putting the hours in is one part of the puzzle, but to optimize rest, it’s helpful to understand the stages of sleep.

There are two sleep stages: non-rapid eye movement (NREM sleep) – broken down into three sub-stages – and rapid eye movement (REM sleep). It takes the body approximately 90 minutes to cycle through all these stages, meaning most people experience 4-6 sleep cycles every sleep period. (1)

What Is NREM Sleep?

The sleep cycle starts with NREM (AKA non-rem) stages one, two, and three before progressing to REM and starting all over again. NREM stage one accounts for around 5% of sleep time and is characterized as the transition from wakefulness to sleep. This is the lightest stage of sleep as muscle tone persists and breathing continues at a regular level. (1)

After around five minutes, sleep progresses to NREM stage two, where the body temperature and heart rate drop, and you sleep more deeply. (1) Now, the brain initiates two unique forms of activity: sleep spindles, which help with memory and learning and block out external stimuli to keep you asleep, and K-complexes, which help block reactions to harmless light or sounds and wake you up if something is perceived as dangerous. Stage two of NREM accounts for about half the time we are asleep.

NREM stage three is known as ”slow-wave sleep” or deep sleep. This stage is integral to repairing and restoring the body, building bone and muscle, and strengthening the immune system. This leads to waking up feeling refreshed in the morning. As people get older, however, they tend to spend less time in slow-wave sleep and more time in NREM stage two. (1)

What Is REM Sleep?

Rapid eye movement (REM) sleep is an active sleep stage most closely associated with dreaming. During this time, the arm and leg muscles become temporarily disabled, preventing the body from acting out when dreaming. (2) The eyes and diaphragmatic breathing muscles remain active, and breathing becomes more erratic and irregular. The first REM cycle usually begins around 90 minutes after we fall asleep and occurs after NREM sleep stages one to three. The first period of REM sleep at the start of the night lasts for around 10 minutes and then gradually increases, with the last cycle lasting up to one hour. (1)

It might not feel like it on Monday morning, but we spend around one-third of our life asleep as humans. The homeostatic need for sleep – our sleep drive – and a wake-promoting process that heightens during the day to keep us energized and alert regulates the sleep-wake cycle. As day returns to night, the wake-promoting process eases, allowing the sleep drive to take over and enhance the possibility of a deep, restful slumber. When adequate rest is achieved, the wake-promoting process fires up, and the cycle begins again. (3)

Speaking of our normal sleep-wake cycle, our breakthrough BioSeries™ technology in our Sleep BioSeries™ Melatonin moves to the beat of our normal sleep rhythm. The melatonin is released in phases to support falling asleep and staying asleep to wake up rested.*

How Many Hours of Sleep Do We Need?

A research panel for The National Sleep Foundation agreed that newborns should sleep between 14 and 17 hours in a 24-hour period, toddlers between 11 and 14 hours, preschoolers between 10 and 13 hours, and school-age children between 9 and 11 hours. For teenagers, 8 to 10 hours was considered adequate, 7 to 9 hours for young adults and adults, and 7 to 8 hours for older adults. (4) The Centers for Disease Control and Prevention (CDC) reports that one in three adults in the United States are not getting the recommended amount of sleep each night. To help build sleep habits that support sleep health, the CDC has some recommendations:
• Avoid alcohol, large meals, and caffeine close to bedtime
• Go to bed and wake up at the same time each day
• Create a quiet, dark, and relaxing room for sleeping in
• Remove electronic devices from the room you’re sleeping in before bedtime
• Exercise or be physically active throughout the day

Don’t Snooze On Sleep Health

Sleep is unconscious by design, but this vital body and brain function should be optimized for overall health. Getting enough sleep isn’t enough—the quality and duration of our sleep cycles and our ability to follow our own circadian rhythm or internal body clock are all integral to getting the restorative rest we need.

References:

1. Patel AK, Reddy V, Shumway KR, et al. Physiology, Sleep Stages. [Updated 2022 Sep 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526132/

2. National Institute of Neurological Disorders and Stroke. “Brain Basics: Understanding Sleep. https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep. Accessed September 14, 2023.

3. Reddy S, Reddy V, Sharma S. Physiology, Circadian Rhythm. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519507/

4. Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, “CDC - How Much Sleep Do I Need? - Sleep and Sleep...” 2 Mar. 2017 Link

5. Arendt, J., & Aulinas, A. (2022). Physiology of the Pineal Gland and Melatonin. In K. R. Feingold (Eds.) et. al., Endotext. MDText.com, Inc.

6. Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors. ... Sleep Deprivation: An Unmet Public Health Problem. Washington (DC): National Academies Press (US); 2006. 2, Sleep Physiology. Available from: https://www.ncbi.nlm.nih.gov/books/NBK19956/#

7. Karasek M. (2004). Melatonin, human aging, …. Experimental gerontology, 39(11-12), 1723–1729. https://doi.org/10.1016/j.exger.2004.04.012

8. Reddy S, Reddy V, Sharma S. Physiology, Circadian Rhythm. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519507/