In 2017 the Nobel Prize in Medicine was awarded on sleep. The work explained sleep's impact on our behaviour, body temperature, immune system, blood pressure, hormones, and digestion. It did this by showing how every cell in the human body independently goes through the same morning, afternoon and evening workday that you do.

If you take human cells and keep them alive in a petri dish they function differently at various times of the day and go through the same cycle every day, like clockwork. A step smaller, even our genes work depending on a day and night rhythm. 

We are but the sum of our parts. Life evolved to a cycle of light and dark, and our mental and physical health can be dramatically impacted by following or neglecting it's adapted 24-hour, or “circadian”, rhythm. 

Circadian rhythm is the largest known regulatory system in our bodies, informing our bodies how to run best, where to divide labour when to turn housekeeping on at rest or active mode during the day. Sleep determines whether that rhythm is in or out of sync.

Is It OK To Get 5 Hours Sleep?

We think we know the answer, but the question: "how much sleep is enough sleep and is more better?" was only validated by controlled study as recently as 2009.
Researchers found the magic number of hours to sleep a night is 7, and that number is magic, minimising the overall risk of cancer, stroke, and heart disease. 

What about 12 hours? Intuitively we could predict if you sleep fewer hours mortality goes up, but also, in a cohort of 98,634 subjects they found sleeping longer than 7 hours per night actually increases mortality.

Sleep And Immunity

Sleep is your best weapon come flu season. Myth? This is another one we didn't know for certain until 2009. It was a productive year for the science of sleep.
If someone with the flu sneezes on you, you're likely to get sick. Researchers dripped the common flu virus directly onto participants' nostrils. Whilst some contracted the flu a significant number of participants did not. 

Those who didn't have a strong immune system. The study found the best predictor of immunity health was the number of hours slept per night. 

Participants with under 7 hours of sleep were 3 times more likely to develop a cold than those with over 7 hours of sleep. Sleep is one of the best predictors of immunity beating weight, mental health, demographic, lifestyle, and season of the year.

Sleep Quality, Your Smartphone & Weight Loss

Candles and electric light are on the red and yellow end of the light spectrum. Smartphones and laptops with fluorescent and LED lights emit blue light, which is special because your brain thinks it's morning sunlight. 

Typing out a ten pm email can confuse your brain by lowering levels of the hormone melatonin and disrupt your circadian rhythm: your body thinks it's bedtime whilst your laptop informs you it's dawn. This can not only impact sleep but your weight too.

In one study, researchers used wrist meters to measure participant's nighttime light exposure finding it correlated directly with increased risk of developing obesity. In another of 100,000 women, researchers found that women with higher exposure to light at night were likely to be significantly heavier.

It's possible those sleeping in better lit bedrooms have poorer sleep quality and suffered metabolic consequences. What is certain is that light at night impacts circadian rhythms and weight, with scientists even able to correlate residential areas well lit during the night hours with higher population rates of obesity.

Night Shifts & Sleep Eating

Your body monitors whether you're sleeping during the night and awake during the day by aligning your sleeping with your circadian rhythm. 

Switching things up, for example, working night shifts can have negative long-term health consequences with researchers correlating night working with higher rates of death from heart disease, stroke, cardiovascular disease, and cancer.
Night workers are also at risk of nighttime eating. Studies placing participants on the same diets, same number of hours of sleep, but at reverse times of the day resulted in elevated cholesterol, blood pressure, and inflammation. 

Waking up mid-sleep and popping to the fridge can also cause more weight gain than if the same number of calories are eaten during the day. This is because you burn 12-16% fewer calories during your body's allotted "sleeping hours". 

Additionally, if you are to eat when your body would rather be asleep, what you eat matters more. A snack at 11 pm burns 6 grams of fat less than the same snack eaten at 10 am, and a 9% bump in bad cholesterol within 2 weeks when continuing to eat at night. 

We underestimate the impact of sleep on our health likely because we have some conscious control over it. The number of hours you get, your quality of sleep, and how sleep fits into your lifestyle are vital. 

Better sleep means more energy to exercise, better metabolism and can help combat the development or symptoms of depression and anxiety. If you're struggling to find where to start for a healthier lifestyle, your sleeping habits can be a great first step.

Appendix.

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