How many people do you know are able to, on a daily basis, sleep long enough to feel fully rested when they wake up? Who is able to go through the day without being at some point sleepy or feeling the need to take a nap? In contrast to a few decades ago, we have the tendency to sleep less. Increased competitiveness in the business world forced people to work for longer hours, and new technologies makes our lives busier.

One of the direct consequence of lack of sleep is obviously fatigue throughout the day. Most of us will try to fight it with a good cup of coffee in the morning or energy drinks during the day. Unfortunately, fatigue is only the tip of the iceberg and a poor sleep will cause more severe damages to our metabolism. Here is how…

Circadian Rhythm

In order to understand better how our metabolism is linked to our sleep, let’s take a look into our central nervous system. Our body is regulated by the circadian rhythm or circadian clock, which is also known as our “biological internal clock”. It is the system that regulates your sleep-wake rhythm and it is intimately influenced by the sunlight.

Humans are not the only one who have that biological clock. Other mammals, plants, and even fungi or bacteria are driven by their own circadian clock. It will for instance indicate to some animals when to hibernate or to migrate. It also tells plants when to flower for the best chance of attracting pollinators.

Hormonal levels

In humans, the circadian clock consists of a group of cells located in the hypothalamus, which is the part of the brain that control our autonomic system, i.e. the system that regulates or internal organs and their function (heart rate, blood pressure, digestion…)

The hypothalamus will give orders to our glands to secrete hormones, which role is to create change in our metabolism in order to adapt to a change in our environment. An example is the melatonin, secreted by the pineal gland, which is a hormone involved for falling asleep among other functions. Another example is the cortisol, a steroid hormone produced by the adrenals, which is involved in response to stress and increase blood sugar levels, which stimulate our arousal.

Adverse reaction to poor sleep

Multiple scientific studies have shown that poor sleep will disrupt our circadian clock, which will affect our ability to regulate our hormones properly. So, what are the most significant adverse effects of poor sleep?

  • It affects the appetite

Our appetite is largely affected by two hormones, leptin (the satiety hormone) and ghrelin (the hunger hormone). Low levels of leptin and elevated levels of ghrelin increased our feeling of appetite. It has been shown that poor sleep will decrease leptin levels and increase ghrelin, which will cause that impression of being hungrier than we actually are.

  • Decrease in glucose tolerance

A poor sleep will raise cortisol levels, which will raise blood glucose level. This will force our body to work even harder to lower of blood glucose level.

  • Increased obesity, diabetes and risk of cardiovascular diseases

This is a direct consequence of the previous point. Sustained high glucose levels in the blood will cause increase risk of obesity and diabetes. Multiple studies have also linked it with hypertension and increased risk for cardiovascular diseases.

  • Poor focus/attention

A collateral effect of hypertension is narrowing of blood vessels. This narrowing will decrease the blood supply to the brain, which will limit its oxygen and nutrients supply and causing an overall poor brain function. This will translate into difficulty focusing and staying alert.

  • It affects the memory

A study from Harvard Medical School showed that too little sleep might affect memory. Interesting thing is that too much sleep might also affect the memory in a negative way.

  • It affect our gut function

Recent studies suggest that the gut bacteria, highly responsible to our digestive function, are sensitive to our melatonin levels. Our gut has a huge influence on our immune system and our nervous system.

What can be done?

This shows that if you need to drop weight for a competition or if you need to study for an exam, it might not be a good idea to stay awake for late hours. Here is what can be done:

  • Go to bed at a regular time and set up a bedtime routine. This could be for example listen to mellow music, stretching, deep breathing exercises, reading something not too demanding for your brain…
  • Avoid spending time in front of the TV, computer/laptop, or cell phone before to go to bed. A screen is like a flashlight in your face, it will keep your brain excited
  • Avoid drinking coffee, soft drinks, or eating food rich in carbohydrates. Those should be avoided at all time, but even more in the afternoon or evening.
  • One of the best way to fall asleep early is to move your body and to exercise throughout the day and avoid staying on the couch for too long, especially in the evening.
  • Finally, a lot of people use over the counter melatonin or even more aggressive sleep aid pills. I would not recommend those since the side effects might be dangerous and further deregulate our hormonal levels. A integrative medicine doctor will tell you what are the healthy options to support your sleep pattern in a natural way.


Arlet V. Nedeltcheva, MD and Frank A.J.L. Scheer, PhD. Metabolic effects of sleep disruption, links to obesity and diabetes. Curr Opin Endocrinol Diabetes Obes. 2014 Aug; 21(4): 293–298.
Guglielmo Beccutia, and Silvana Pannain, Sleep and Obesity. Curr Opin Clin Nutr Metab Care. 2011 July ; 14(4): 402–412
Rachel Leproult and Eve Van Cauter. Role of Sleep and Sleep Loss in Hormonal Release and Metabolism. Endocr Dev. 2010 ; 17: 11–21.
– Jiffin K. Paulose, John M. Wright, Akruti G Patel, Vincent M. Cassone. Human Gut Bacteria Are Sensitive to Melatonin and Express Endogenous Circadian Rhythmicity. PLoS One. 2016; 11(1): e0146643.

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