In short – yes, we do. Our bodies need the energy to support the activity of our vital organs, such as the heart and lungs, which keep working while we sleep.
During deep sleep, or slow-wave sleep, our body cells are restored as the human growth hormone is released. Our brains are very active during the REM sleep stage – the stage in which we experience the most vivid dreams and during which many different centers in the brain get randomly activated. Non-REM sleep requires significantly less energy.
However, we do spend a lower amount of energy while sleeping than we do during wakefulness. Even simply lying in bed awake takes up more energy than sleeping, but not every person consumes the same amount of energy – it depends on a number of factors. Even so, you can still influence the total energy consumption during sleep.
Poor sleep habits have a significant influence on our response to stressful situations, hormone excretion, and metabolism. It disrupts many systems in our body, including how much energy is used while sleeping.
Do we sleep so that we can save energy?
Evolutionists offer an explanation to what may be the main purpose of sleep. Taken that humans are warm-blooded, they, just like other warm-blooded animals, need a significant amount of energy to retain body temperature and keep the important body functions running. For example, although small, our brains use 20% of our total energy. Sleeping helps us ‘recharge’ and retain the valuable energy.
During sleep, our energy expenditure levels decrease by 5-10% – metabolism slows down, body temperature decreases, heart rate and breathing also slow down.
On the other hand, cold-blooded animals require significantly less sleep time, making this theory plausible.
However, although it does offer some energy conservation, if we consider other benefits of sleep (body restoration, memory consolidation and learning, early brain development, hormonal balance, immune system benefits and more), we would have to agree that the primary function of sleep is not energy saving.
How much energy does our body use while sleeping?
The amount of energy spent depends on body mass, physical fitness, age, quality and quantity of sleep, and sleep environment.
Those who weigh more typically consume more calories while sleeping. However, not every 180lb person will use the same amount of energy. Those who are younger and have more physical activity need more energy because their muscle mass is greater (muscles consume glucose and fats) and have a faster metabolism.
When it comes to sleep quality and quantity, we know that we spend the most energy during REM sleep (it is when heart rate, breathing, body temperature, and brain activity increase). REM is one of four sleep stages. In the second half of the night, it occurs more frequently and lasts longer. So if you are unable to get REM sleep, you will consume less energy. Studies have shown that sleep deprivation results in lower energy consumption at night and higher energy intake demand during the day, so a lack of sleep may lead to overeating and body weight increase.
Those who sleep in a cold room burn more calories because their body needs the energy to keep a desirable body temperature.
Although some questions were raised regarding the effect of daily light exposure on the night’s energy expenditure, research has shown very little or no effect that daylight had on the nightly calorie consumption.
An average person consumes about 0.42 calories per pound (of body weight) in one hour of sleep. So the calculation for a 180lb person with 8 hours of sleep would be as follows:
- 0.42 x 180 = 75.6 calories per hour
- 75.6 x 8 = 604.8 calories per night
Note that 0.42 is an average value and that this calculation does not consider age, fitness, sleep environment or sleep quality. This can serve as an interesting estimation, to help us at least get an idea of how much energy our bodies might be spending.
How to burn more calories while sleeping?
In order to burn more calories while sleeping, these are the steps you can take:
- Sleep regularly and sufficiently. If you take good care of your circadian rhythm, meaning you go to sleep and wake at approximately the same time, you will increase the chances of having more REM sleep, which means higher calorie consumption.
Sleep restriction seems to result in spending extra energy, even if a person just lies awake in bed. However, food demand after a period of sleep deprivation is higher and recovery sleep after this period required less energy. To explain additionally, depriving yourself of sleep will burn more calories in the short term, but the sleep following that period will be focused on restoring the energy balance. Apart from confusing your circadian rhythm, you may also end up gaining weight and impairing your overall health. Sleeping longer gives you the chance to burn more calories.
- Don’t sleep too much. Although sleeping longer does increase your sleep energy consumption, it doesn’t mean you should sleep more than you need, as this will reduce your metabolic rate – and slow metabolism equals weight gain. This means neither of the extremes – getting too much nor too little sleep – is good.
- Have a small, light meal before bed. Eating calorie-rich food in large portions will make it difficult to fall asleep. Another drawback of late night meals is that our body doesn’t get to metabolize food thoroughly. As a result of the human growth hormone release, the food isn’t used for energy consumption, but rather for storage in the form of fat.
- Don’t drink alcohol before bed. Alcohol consumption prevents you from reaching REM sleep.
- Exercise regularly. More muscle mass and fitness will increase your energy expenditure, which means that exercising pays off even hours after you’ve finished with your training.
- Turn the heating down by a few degrees or sleep with a thin blanket. Give your body the chance to warm up naturally and burn some extra calories.
Following all the rules of proper sleep hygiene not only will help you with the energy consumption, but it will also ensure you get a good night’s sleep.
Energy use during sleep versus sleep-related and sleep-unrelated disorders
A study from 2015 has shown that sleep loss, stress, and poor metabolism may be interconnected with insomnia, diabetes and obstructive sleep apnea.
Living under constant stress during wakefulness, with insufficient hours of sleep (and poor quality of the actual sleep) can strongly interfere with the proper function of some of the most important glands in our body – the hypothalamus, pituitary, and adrenal glands.
The hypothalamus contains a group of neurons called the ventrolateral preoptic nucleus (VLPO). It makes one of two poles of the flip-flop switch which regulates our sleep-wake process. Another important function of the hypothalamus is its high involvement in the function of the pituitary gland, which is located just below the hypothalamus.
The pituitary gland, among other hormones, secretes growth hormone, which restores and heals the body during sleep, adrenocorticotropic hormone, produced in stress, and thyroid-stimulating hormone, which stimulates the thyroid gland to produce its hormones. Thyroid gland hormones promote metabolism in almost every cell in the human body.
Finally, adrenal gland produces vital hormones such as cortisol – it also regulates metabolism and the way our body responds to stress. Another hormone we are not able to live without is aldosterone, and it helps control the blood pressure.
These three together are known as the hypothalamic–pituitary–adrenal (HPA) axis. A disruption to the HPA axis may result in an inability to fall asleep, developing narcolepsy, or metabolic problems.
For example, chronic stress may result in poor sleep, which then may lead to dysfunction of the metabolism and excessive daytime sleepiness. Over time, metabolic problems play a role in developing diabetes, which as a symptom may have obstructive sleep apnea. While experiencing constant fatigue and irritability, one’s mental health is impaired, which leads to more stress and maybe even depression.
Therefore, in order to break this vicious circle, or prevent it from ever happening, make sure to have plenty of healthy nighttime rest. Also, instilling good sleep habits in your children from an early age will play a major role in their mental and physical health not only while they are kids, but also after they grow up.
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