We envy them for needing very little sleep while going crazy for long days. These little sleepers who only abandon themselves to the arms of Morpheus for four to five hours a night have a lot more time to enjoy life, the lucky ones! But are they really immune to all these evils to which lack of sleep predisposes?
True short sleepers, that is to say those who are endowed with genetics that allow them to recover well after only a few hours of sleep, are very few in number. “They represent only a tiny fraction of people who call themselves short sleepers,” says Andrée-Ann Baril, postdoctoral fellow in neurology and epidemiology of sleep at the Douglas Research Center and McGill University.
Studies have indeed shown that some people who function very well with four to five hours of sleep per night carry mutations in certain genes involved in the regulation of sleep. One of these mutations, which had been identified in around fifty families of short sleepers, was transplanted into mice. However, “in these genetically modified mice which tended to sleep less, the cerebral centers responsible for awakening were activated more. We therefore think that this is one of the reasons why some people sleep less and are more resistant to sleep deprivation,” says Nadia Gosselin, scientific director of the Center for Advanced Studies in Sleep Medicine.
“It’s possible that people with a genetic predisposition to sleep less sleep more efficiently, so they need fewer hours of sleep. Therefore, they would not be at risk of developing diseases related to lack of sleep, ”says M.me Barrel.
“The majority of short sleepers aren’t like that though. Often they sleep little due to their work habits, for example. Even if they don’t feel like it’s affecting their functioning, if we test them cognitively, we will see decreases in performance. But since they are used to operating like this, they think they are correct. However, that does not mean that they are functioning to their full potential and that they are not at risk of suffering from certain diseases,” warns the researcher.
The danger of little sleep
We know that the majority of risks appear when we sleep an average of six hours or less per night. However, it is not known from how many years of sleep deprivation this risk begins to manifest itself, she specifies.
Numerous studies have in fact shown that chronic lack of sleep increases the risk of suffering from various pathologies, such as obesity, diabetes, hypertension, heart disease, depression and dementia, including Alzheimers. How does sleep deprivation predispose to these diseases?
Sleep is known to play a role in hormonal regulation. A lack of sleep can induce a decrease in the secretion of leptin, the satiety hormone, and an increase in that of ghrelin, the hunger hormone. People who are victims of such a hormonal imbalance will be hungrier during the day and will seek foods with more calories, all factors that will contribute to the development of obesity.
“If you want to lose weight, it is important to sleep well, because not sleeping will make it more difficult to achieve this,” notes Ms.me Gosselin.
Studies have also shown insulin resistance in short sleepers and insomniacs. “However, this insulin resistance is the initial stage of type 2 diabetes, which can also be a consequence of obesity”, underlines Mme Barrel.
Research has also found a slightly higher than normal level of inflammation in people with certain sleep disorders. “If we shorten the duration of sleep, we compromise the optimal regulation of the immune system, with the result of activating inflammation. However, inflammation of the blood vessels will create atherosclerosis, which will promote the development of hypertension, which will contribute to coronary heart disease,” explains the scientist.
In addition, during sleep, blood pressure naturally decreases, especially during the deep sleep stages. “However, people who do not sleep enough or who have fragmented sleep do not have this decrease in blood pressure, and the fact that the latter remains high for longer during the 24 hours of a day would be harmful to the blood vessels. blood levels and predisposes them to hypertension and cardiovascular disease,” says Ms.me Barrel.
Lack of sleep can also disrupt the regulation of the autonomic nervous system, which can then find itself in a state of hyperactivation, which will lead to an increase in blood pressure likely to induce damage to blood vessels and consequently hypertension with cardiac consequences, she says.
Stress and emotions
Sleep also allows us to better manage our emotions. It regulates communication between the amygdala, the emotional management center in the brain, and the prefrontal cortex, which is particularly responsible for executive functions and has an inhibitory effect on the amygdala.
According to neuroimaging studies, “the inhibition exerted by the prefrontal cortex would not be as effective when we do not sleep enough, which would allow the amygdala to speak a little more freely, and would therefore lead to emotional states less controlled, irritability and possibly depression,” explains Andrée-Ann Baril.
Short nights of sleep can also compromise the regulation of the axis linking the hypothalamus, the pituitary and the large adrenals, regulation which intervenes in the management of stress and its hormone, cortisol. In people whose sleep is of short duration, there would be an activation of this axis which would induce a state of wakefulness and higher stress likely to lead to a depressive state, adds the researcher.
The Alzheimer’s Question
Several hypotheses have been put forward to explain the possible role of lack of sleep in the onset of Alzheimer’s disease.
The first is related to the essential role of sleep in the consolidation of memory.
According to the second, the pro-inflammatory state caused by the lack of sleep could contribute to “the neuro-inflammation that we see in Alzheimer’s”, underlines Mr.me Barrel.
And the third stems from the discovery of the increased cleaning activity that the lymphatic system performs in the brain during sleep. As this cleaning eliminates in particular the tau and beta-amyloid proteins, the accumulation of which causes Alzheimer’s disease, it is thought that inadequate sleep would limit the elimination of these toxic metabolic wastes, which would damage the brain in s accumulating.
“The number of hours of optimal sleep to preserve one’s health is around seven hours a night for the majority of adults”, recalls Mme Gosselin.