I recently got an upgrade on my Garmin watch which tells me info about my sleep the night before. I have been curious and intrigued by these graphs with amounts of each sleep stage and wanted to know more about how much of REM, deep, light sleep is normal or enough. This lead me to do some research and reading from the National Library of Medicine. I have summarized and hopefully helped make sense of some of the medical terms below, if you want to skip the detailed info part on sleep scroll down to the end for the 5 sleep tips, but if you are curious like me let’s learn more about sleep……
There are 2 phases of sleep that we cycle through, (1) rapid eye movement (REM) and (2) nonrapid eye movement (NREM) sleep, which is further divided into 3 stages –N1 to N3.
Each various phase of sleep includes different levels of muscle activity, brain wave patterns and various eye movements. Each night we cycle through these various phases about 4 to 6 times, averaging 90 minutes for each cycle.
Sleep quality or the time spent in each sleep stage can be altered by various factors such as aging, brain injuries, medications, circadian rhythm issues like variations in cortisol, stress levels.
The duration spent in each sleep stage evolves as we age, often requiring less sleep as we get older.
Newborns sleep approximately 16 to 18 hours per day.
At 12 months infants typically sleep 14 to 15 hours daily.
Around 2 – 5 years the total sleep time needed decreases from 13 to 11 hours.
By age 6 children set in their preference early on toward being night owls or early risers (Larks). This pattern will last our lifetimes and we should work around sleep times that suit and not have to stick to set bedtimes.
Age 10 to 18 in our adolescent years the amount of sleep is around 9 to 10 hours each night, changes occurring in slow wave sleep accompanying puberty.
Adults 18+ tend to show reductions in sleep overall.
Ages 65 and older awaken on average 1.5 earlier.
Gender differences men sleep more in stage N1 and women maintain slow wave sleep longer and can have more trouble falling off to sleep.
The current understanding of why sleep is an essential part of life is not clearly understood, but it’s thought that the primary value of sleep is to restore brain balance and overall health. Some current ideas on what the functions of sleep are:
1. Helping brain cells mature
2. Learning and memory
3. Decluttering brain nerve networks
4. Thinking
5. Clearing waste products produced in the awake brain
6. Building up energy reserves
The 5 stages of sleep with each stage progressing downwards towards deeper sleep are:
1. Stage W (Wake Stage) – beta waves high frequency low altitude, alpha waves (quiet relaxed wakefulness) occur as we become drowsy
2. N1 (5% of our total sleep) – Non REM (NREM) theta waves the lightest stage of sleep begins when more than 50% of alpha waves are replaced with low amplitude mixed frequency activity. Lasts 1- 5 minutes, 5% of total sleep. Muscle tone is active, breathing regular.
3. N2 45% NREM – powerful bursts of neurons firing, helping nerve activation, and consolidating memory. This is the majority stage, deeper sleep occurs as heart rate and body temperature drop. Delta waves the longest of all brain waves occur maintaining sleep and memory lasts around 25 minutes in the first cycle and lengthens with each successive cycle, comprising around 45% of total sleep. This stage of sleep grinding of teeth may occur.
4. N3 25% deepest NREM, delta waves lower frequencies higher amplitudes. This stage is the most difficult to awaken from, for some noises >100 decibels will not awaken. As people age we spend less time in this slow delta wave stage and more time in N2 sleep. If awaken in this stage we may experience some fogginess which could last 30 minutes to 1 hour afterwards. This stage is when the body repairs and regrows tissues, build bones and muscles and strengthens the immune system. Sleep walking, night terrors and bedwetting may occur in this stage.
5. REM 25% – beta waves similar to brain waves in awake brain. First part night it’s short as night progresses, longer REM and less NREM. This is sleep phase we dream in and is not considered a restful stage. The brain waves may be similar to that of the awake brain but the muscles are without movement except for the eyes and diaphragm for breathing, however it is more erratic and irregular. This stage usually start 90 minutes after the sleep stage, and with each REM cycle increases in amount. First cycle lasts 10 minutes final cycle lasting up to 1 hour. Interesting that we use more brain oxygen in this stage, tend to awaken spontaneously in the morning during REM stage, blood pressures varies, highly active brain function during this stage increasing brain metabolism up to 20%.
4 – 5 cycles of the above with one complete cycle taking 90 -110 minutes.
As we humans spend one-third of our lives sleeping, understanding more about this part of ourselves is significant. Lack of sleep affects
Our memory, Ability to think clearly
Can lead to depression
Mood swings, Hallucinations
Add an increased risk for Obesity, Diabetes and heart disease.
Affecting our wellbeing and quality of life, family life and our ability to care for ourselves and children.
Insomnia is having a difficulty falling or staying asleep affecting our daytime function, and can occur despite opportunity for sleep. With almost 105 of our population experiencing it. We have some pharm options like benzos, anti histamines, melatonin, and anti-depressants, anti convulsants or non-pharma options available for the treatment. Like cognitive behavioral therapy (CBT). Alcohol, benzodiazepines, and barbiturates are associated with decreased quality of REM sleep.
Dr Sandra’s 5 Sleep Hygiene Tips:
- Put away phones, tablets computer and TV 1 hour before your regular bedtime
- Make your bedroom as dark as possible, (darkness releases melatonin which declines from age 15 onwards).
- Have a warm shower before bedtime
- Use magnesium glycinate 400 mg, GABA and possibly melatonin as natural sleep aids
- Get your cortisol levels tested to individualise herbal adaptogens to balance the adrenal stress during the day for better sleep at night
Reference National Library of medicine, January 2024