Functions Of The Body When We Sleep
Many things happen during sleep that we may not feel or notice
Sleep is a science of its own. Have you ever wondered why sleep is so important and what happens when we sleep? The reality is that sleep does more than keep us energized and focused the next day, or regenerate and heal our skin. Many things happen during sleep that we may not feel or notice.
Psychological Factors
The brain is actively working as we sleep. 75% of our sleep is spent in Non-REM sleep and the remaining 25% is spent in REM sleep. There are 3 stages of Non-REM sleep. The brain becomes less responsive and it becomes harder to be woken up as sleep approaches Non-REM stage 3. REM sleep is when the eyes dart back and forth behind our lids. Our “fight or flight” nervous system becomes very active, but our bodies are completely still. REM sleep is also when our brains clear information that we don’t need that allows for better focus after waking up. Brain activity during Non-REM sleep is more steady, while brain activity during REM sleep is more similar to when we are awake. Long term memory and processed during Non-REM stage 2 and dreams occur most during REM sleep.
Biological Factors
Our body temperature decreases as we become drowsy and is at its lowest around 2 hours before we normally wake up. We are most affected by the cold or heat from room temperature when we are in REM sleep because the body’s thermometer is shut off during this time.
Breathing becomes more slow as steady as we fall asleep, but becomes faster and more varied during REM sleep.
Similar to breathing, blood pressure, heart rate, and pulse are lowered during Non-REM sleep but will increase and vary during REM sleep.
During any period of deep sleep, our bodies work to repair muscle, organs, and other cells. Chemicals that work to strengthen the immune system begin to circulate in the blood. We spend approximately 20% of the time in deep sleep. However, deep sleep can decrease to 0% of sleep time as age.
Hormones
Our bodies produce more or less of certain hormones during sleep. Hormones with growth and restoration functions increase while hormones associated with stress decrease. Lack of sleep can interfere with production of hormones that are responsible for different sensors, such as hunger and weight gain.
Cortisol, also known as the stress hormone, helps regulate other hormones. Lack of sleep can have negative effects on cortisol production as too much cortisol can increase stress and too little cortisol can affect production of other hormones.
Estrogen and progesterone help maintain reproductive health. As estrogen levels decrease, progesterone levels increase, and vice versa. Estrogen and progesterone also play a function in preventing sleep apnea.
Thyroid hormones help with metabolism. Thyroid hormones also correlate to weight and energy storage and expenditure. Low production of thyroid hormones leads to slow metabolism, which leads to slower transformation of food into energy. Slow metabolism also leads to more production of hunger hormones, ghrelin and leptin. Therefore, we feel hungry easily.
Melatonin is associated with the body’s sleep wake cycle, also knows as the circadian rhythm. Lack of sleep can affect melatonin production and its role in future promotion of sleep.
Growth hormones increase during sleep, increasing the body’s immunity, muscle development, as well as protein production and synthesis. Lack of sleep leads to lack of growth hormones, and eventually decreased availability to repair injuries.
Calories
Our bodies actually burn calories on a daily basis even if we are not active, including when we sleep, although not enough to make a difference in weight. Men generally burn more calories than women because they have higher muscle mass. The amount of calories burnt also depends on weight. The higher the body weight, the more calories burnt while resting or sleeping. Adults burn an average of 50 calories per hour of sleep, but this also depends on various biological and health factors.
Sleep is an important factor of our lives. Despite us getting the necessary rest, specific brain and biological activities take place during sleep in order to help us recharge and prepare for the next day.
References:
Fresh, P. & Baby, D. P. (2022). What happens when you sleep? WebMD. https://www.webmd.com/sleep-disorders/ss/slideshow-sleep-body-effects
Marcin, A. & Bubnis, D. (2018). How many calories do you burn while you’re asleep? Healthline. https://www.healthline.com/health/calories-burned-sleeping
Vinall, M. & Dasgupta R. (2021). How sleep can affect your hormone levels, plus 12 ways to sleep deep. Healthline. https://www.healthline.com/health/sleep/how-sleep-can-affect-your-hormone-levels#hormones-and-sleep
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