To sleep or not to sleep, a health issue
Sleeping well, i.e. getting adequate restful sleep, increases life expectancy and, above all, increases the quality of our lives
BarcelonaSleep is a natural and necessary state of rest of the body and mind in which consciousness decreases and sensory activity is relatively inhibited. The response to external stimuli is minimal, at least the mild ones, however, despite the state of relative unconsciousness, the level of brain activity remains high. In fact, this is the main difference between sleep and other states of unconsciousness, such as coma. All vertebrates sleep and at least some insects, such as flies and ants, are known to sleep, indicating that sleep is of transcendental importance for the life of animals. However, not all animals sleep in the same way.
People, for example, usually sleep an average of 8 hours a day, although there is a certain variability that does not affect a good rest. Cats, to cite another case, sleep 70% of the time, and there are mammals such as whales and dolphins that never sleep at all: for a while one brain hemisphere sleeps and the other remains fully awake, and then they exchange the state. As for insects, it has been found that flies sleep for several periods each day, during which they remain still and indifferent to mild external stimuli. And in the case of ants, while they sleep they are also insensitive to soft stimuli and their antennae relax and hang down. For animals that communicate largely by sending and receiving signals with their antennae, this relaxation would be our equivalent of closing their eyes. Queen ants sleep 90 times a day, six minutes at a time, while worker ants sleep 250 times a day, but only for one minute.
If all or almost all animals sleep, it means that this state of semi-consciousness must play a crucial role in life. What happens when we sleep and what are the effects of sleeping little, or badly?
- During sleep, a series of processes take place that are essential for maintaining the balance and homeostasis of the various systems that make up the body. Homeostasis is the tendency to maintain internal stability, which favours good general functioning.
- On the one hand, renewal and repair processes of the muscular and skeletal system take place. Daily activity keeps the muscles active, which means that small tears can occur in the muscle fibres and waste substances produced by normal cellular metabolism accumulate. The muscular inactivity that occurs during certain phases of sleep allows these waste substances to be eliminated. In addition, when we sleep, the body produces a growth hormone much more intensely, which stimulates the formation of new muscle cells and the repair of broken fibres.
- The endocrine system also benefits from good sleep hygiene, i.e. good sleep, which has an impact on all bodily functions. During the day, one of the neurohormones that helps maintain a good mood is serotonin. At night, melatonin predominates, but to maintain a good homeostatic balance, it is necessary to alternate between serotonin during the day and melatonin at night. These hormonal oscillations reduce the production of another hormone, cortisol, which is related to stress. Getting a good night's sleep therefore improves mood, promotes proper psychological functioning and reduces stress.
- During sleep, the immune system also uses available metabolic energy that is not used for any other activity to regenerate itself. In addition, during sleep, the body produces cytokines, specific proteins involved in the activation, coordination and regeneration of immune system cells, which support and enhance the immune response. Cytokines are produced and released during the deep sleep phase, so it is doubly detrimental if sufficient levels cannot be reached.
- Sleep is also correlated with changes in brain organisation and structure. While we sleep, the brain is very active, but the fact that we are not consciously using it for any particular task allows it to use all available energy to eliminate the waste substances it has accumulated during the waking state as a natural product of its metabolic activity and to repair neuronal integrity. In addition, the synaptic connections between neurons, which are the basis of memory and learning, are remodelled. In other words, while we sleep, everything we have learned during wakefulness is consolidated, which frees up short-term memory, and the brain uses it to make connections with previous experiences. Dreams are considered to be a reflection of this activity, in which the brain relates different experiences. For this reason, a dream combines many different elements that are apparently disconnected from each other. All these factors, combined with the maintenance of adequate psychological functions, the enhancement of a good state of mind and the reduction of stress, also favour and enhance the capacity for concentration, attention and reflection.
- The deficient repair and regeneration of the muscular and skeletal system favours the appearance of pain in various parts of the body, usually those that have worked the hardest during the day, such as the lower back if we sit for long hours, or the joints. Lack of sleep can also favour or aggravate fibromyalgia and chronic fatigue, conditions that also affect the quality of sleep, so it is not easy to establish which is the cause and which is the consequence. But there is certainly a link between sleep quality and these disorders.
- Hormonal imbalances due to lack of sleep or poor quality sleep impair psychological functioning, which negatively affects mood and leads to episodes of sadness and depression, while the consequences of stress are accentuated. In addition, other hormones involved in metabolism, such as insulin, are also altered, leading to metabolic disorders such as diabetes, obesity and hypertension. These disorders, in turn, in combination with stress, can also promote cardiac pathologies.
- Lack of coordination and reactivation of the immune system due to lack of sleep or poor quality sleep hampers the immune defence against infectious diseases, such as those caused by pathogenic bacteria or viruses, and reduces the production of antibodies. Antibodies are proteins made by cells of the immune system that specifically recognise pathogens and mark them for destruction by other immune system cells or by the cells themselves, assisted by other proteins. In addition, the immune system also has cells capable of recognising and destroying tumour cells. Lack of activation or dysregulation of these cells, which are called cytotoxic T-lymphocytes, increases the likelihood of cancer.
- Sleep deprivation or poor sleep negatively affects attention, memory and learning, as the brain is unable to consolidate the experiences of the previous day. This causes short-term memory to suffer, which negatively affects the ability to concentrate and assimilate new knowledge, as well as favouring memory loss. Moreover, in combination with other factors, such as stress or a negative mood, which can also be induced by lack of sleep, it increases impulsivity and, consequently, reduces the capacity for reflection and reasoning.