Why is sleep essential for health?

When was the last time you woke up without an alarm clock feeling energized and not needing caffeine? Have you slept well this past week?

The likelihood is not; in a busy, stressful world, where phones demand our attention day and night, worries fight for attention and noise and light invade our bedrooms, it can be difficult to get the quality sleep you need to be on your game. A lack of sleep can hamper executive functions, cognitive ability and productivity, but like so many things health and wellbeing-related, we only really appreciate its value when it’s lacking.

Our bodies are still pretty primitive and basic - there is no gadget or app that can replace good, old-fashioned quality sleep.

Have you ever craved broccoli at 1 am while binge-watching Netflix? Of course not. We crave foods like crisps and biscuits when we are sleep deprived, because sleep decreases glucose to the brain which is its primary fuel source. Our bodies naturally seek out quick forms of glucose even when it’s not healthy for us. Lack of sleep increases activity in the amygdala (the reptilian part of our brain) and decreases activity in the insular cortex and frontal lobe (which are responsible for willpower). So even when we know we shouldn’t eat that biscuit, our willpower to resist temptation is drastically reduced when we are sleep deprived.

Not only does lack of sleep cause cravings and weight gain, it also affects our brain health and memory. When we sleep our glymphatic system, which is responsible for sweeping away all the toxins that have accumulated throughout the day, is ten times more active than it is when we’re awake. In fact, our brain cells shrink about 50% during sleep to allow the those cells to work more efficiently.

Cortisol is often associated with stress, but if we didn’t produce cortisol after exercise or during stressful situations, we would not survive. The key to optimising cortisol is producing it at the right time and at the correct amounts. Normally, your cortisol levels should peak around 6am and drop to their lowest levels around 10pm. If cortisol is high before bed, you’ll have trouble falling asleep. If your cortisol does not stay low overnight, or if cortisol starts spiking early, you’ll likely wake in the middle of the night.

Production of Human Growth Hormone (HGH) is highest during the first half of our sleep - in the delta sleep stage. This is when we achieve our deepest sleep and potential for restoration. That’s why it’s also known as the fountain of youth hormone. HGH aids in building more lean muscle tissue, protects your muscle from breaking down and gives you energy. This means you are able to lose weight more efficiently and maintain lean body mass when you sleep well.

Melatonin is a powerful hormone produced by the pineal gland, which increases our bodies brown adipose tissue and burns white adipose tissue. As we age our bodies naturally lose brown adipose tissue, but research has shown that higher levels support bone health, improve insulin sensitivity, and increase lifespan.

Leptin, the hormone which controls our desire to eat, and Ghrelin, the hormone which controls hunger, are both effected by lack of sleep. Just one poor nights’ sleep reduces leptin levels and increases ghrelin levels, which is why we want to eat more sugar and carbs when we are tired.

If all that wasn’t enough, going to bed late can also increase the risk of heart attacks and strokes. In a recent study of 88,000 people, those who went to bed before 10pm had a 24 per cent increased risk of later developing heart disease, while those who went to bed after midnight saw their risk increase by 25 per cent. People who fell asleep between 11 and 11.59pm had a 12 per cent greater risk. Those who had gone to sleep between 10 and 10.59pm were the least likely to have developed heart problems, the researchers discovered, even after controlling for other variables such as age, sex, duration of sleep, smoking status, body mass index, diabetes, blood pressure and socioeconomic status. It’s thought that 10 and 10.59pm is a key point in the body’s 24-hour cycle, or circadian rhythm, which helps regulate physical and mental function and wellbeing.

But it may not always prudent to get the eight hours usually recommended.

According to a study by Washington University School of Medicine, just like too little sleep, too much sleep was a risk factor for an ageing brain. Getting fewer than 4.5 hours or more than 6.5 hours a night was more commonly seen in those who showed cognitive decline over time, suggesting that it isn’t necessarily the length of the sleep that matters, but the quality of that sleep when it comes to risk of developing dementia.

Sleep quality refers to how much time you spend in deep, restorative sleep, and the study showed that having less “slow wave” sleep - the type where you dream and have rapid eye movement (REM) - was most detrimental to the brain’s health.