Sleeping less hours on a routine basis has immediate and obvious effects, such as tiredness or sluggish thinking, but it also has other negative health consequences that are not so obvious. For example, it increases the risk of developing type 2 diabetes. This is what a study published recently by North American researchers has concluded, after analysing the results of experiments performed with volunteers. Coinciding with World Sleep Day, celebrated on Friday, 16 March, experts from the Universitat Oberta de Catalunya (UOC) explain what we know about the effects that sleeping has on how our body uses sugar and stress the importance of getting enough quality sleep each night.
Diabetes is a disease in which the body is no longer able to regulate sufficiently the blood levels of glucose (sugar), so that it tends to accumulate or remain at high levels. In the case of type 2 diabetes, the problem is that the body does not produce enough insulin or does not use it properly. Insulin is the hormone whose job is to take sugar into the cells so that it can be used as fuel.
Type 2 diabetes is the variant that affects most of the more than 420 million diabetes sufferers around the world. The World Health Organization (WHO) alerts that the proportion of adults with diabetes is increasingly continually and has almost doubled in the last four decades. This trend is worrying because diabetes can damage the kidneys, nerves or eyes and, in turn, increases the risk of suffering cardiovascular or cerebrovascular diseases, such as stroke. But what are the causes of type 2 diabetes and what does sleep quantity and quality have to do with it?
It is known that genetics has an influence on the tendency to develop type 2 diabetes, but it also known that a sedentary lifestyle, being overweight and, especially, obesity, are also very important factors. And now, too, how many hours we sleep: "As the study suggests, we have a lot of data that says that people who have been deprived of sleep in experimental conditions develop insulin resistance", says Diego Redolar, a neuroscientist and researcher at the UOC's Cognitive NeuroLab.
Insulin resistance, the prelude to diabetes
"Insulin is like a key that opens the cells' lock so that the sugar can get in. In insulin resistance, which happens when we have persistently high levels of this hormone, the key no longer fits properly in the lock, not enough glucose enters the cells and they start to complain and ask for more", explains Marta Massip-Salcedo, professor at the UOC's Faculty of Health Sciences.
To compensate for this, the pancreas, the organ that makes insulin, secretes more "so that more doors can open, even if only partially, and the cells can get the glucose they need", the expert continues. "However, in these conditions, the pancreas ultimately loses the ability to secrete enough insulin and, therefore, the blood levels of sugar remain high. It is the prelude to diabetes," she concludes.
Many clues and some mysteries
In fact, insulin resistance is also one of the reasons why obesity causes diabetes. And, in turn, lack of sleep is one of the factors that can cause obesity. Everything is interconnected but, as Redolar underscores, it is still not known exactly why not having enough sleep favours insulin resistance. However, what is known, he highlights, is that there is a part of the brain that is involved in this: "When a person doesn't sleep, the neural circuitry of wakefulness is activated. One of the circuits is the lateral hypothalamus, which has a group of neurons, called orexinergic neurons, that, when activated, not only enhance wakefulness but also encourage food intake, while at the same time slowing down metabolism", he explains.
"The adaptive explanation is that when we are hungry, we can't go to sleep because we have to find food and, at the same time, we slow down our metabolism to reduce energy expenditure; this would also explain why we prefer high-calorie foods when we cut down on sleep", he adds. In addition, the role played by hormones such as cortisol (which is involved in regulating the metabolic processes that release stored energy, thereby increasing the blood sugar levels), leptin (which is responsible for the sensation of being full) or ghrelin (which stimulates the desire to eat) is being investigated.
Eat better, but also sleep better
In any case, it seems clear that to avoid developing diabetes, or to control the disease, it is important to not only eat better, but also to sleep better. "There are many attempts to treat diabetes and obesity that focus on behaviour, and most of them have concentrated particularly on eating behaviour. Perhaps it should also be added that we need to have enough hours of (if possible) unbroken sleep", Redolar observes.
"The good news is that insulin resistance can be reversed by changing eating habits, getting enough sleep and exercising", says Marta Massip-Salcedo. In the case of diet, the expert stresses the importance of not eating too much food containing large quantities of simple carbohydrates, such as processed foods, and also recommends not to snack between meals "so that the pancreas can rest and, ultimately, insulin levels can drop between meals".
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