Here's why insomnia and anxiety make us more fragile against the flu in our youth and beyond

Get the right amount of sleep. And rest well. That way you will defend yourself better against viruses (starting with the flu). And also from bacterial infections. If our grandmothers indicated wool (i.e. staying warm), milk (i.e. light nutrition) and above all bed (i.e. rest) as the three key words for seasonal ailments, today science confirms how right they were. By investigating the cells involved in the body's defensive responses, in fact, it was discovered how real and tenacious is the red thread linking insomnia and the anxiety that can result from it with immune defences. In students with sleep and anxiety-related problems, in fact, the number of Natural Killer (NK) lymphocytes, which represent one of the very first lines of defence: they attack invading pathogens, foreign bodies and infected cells in the initial stages, counteracting their spread, drops. And, as a result, over time there may be a less effective response to immune system perturbations. Detecting this pernicious relationship for health is research published in Frontiers in Immunology by a team from Taibah University, Saudi Arabia (first name Renad Alhamawi).

On the immunological front, a significant drop in NK cells may increase the risk of altered defences and thus a decreased response to certain diseases. The research assessed the association between anxiety, insomnia, and NK-cell counts in 60 female students aged 17 to 23 years, using targeted questionnaires and self-reports of symptoms of sleep difficulties. Using a simple blood sample, the NK-cell populations were then analysed qualitatively and quantitatively in relation to a control population without sleep disorders. 'We found that in female students with symptoms of insomnia, the count and percentage of total NK cells and their subpopulations were decreased,' Alhamawi comments in a note. The same was observed in young women with symptoms of generalised anxiety: in this population, too, there was a decrease in the number of circulating NK cells and their subpopulations. All this, of course, in comparison with those who had no rest problems. The analysis focused on two sub-types of circulating NK cells in the blood: one population is particularly present in the nervous system and in the connections with the rest of the body (these are cells that show cytotoxicity, i.e. they can damage or kill cells that invade the body), the other comes into play in the production of proteins that function as chemical messengers and in the regulation of the immune system. In cases of insomnia and anxiety, these cell populations drop, potentially weakening immune reactions not only against infections, but also in the psychological response to stress.

Insomnia, however, affects immune responses in a much broader way. Suffice it to say that there is a well-explained link between insomnia, pain and inflammation. Sleep disturbances, including the reduction of its duration and continuity, in fact induce a pro-inflammatory state that favours inflammatory reactions and pain. Variations in sleep duration and architecture lead to increased production of cortisol (the stress hormone), norepinephrine and adrenalin alerting units. Poor quantity and quality of sleep amplifies inflammation and pain, thus generating a vicious circle. Conversely, good sleep quality is influenced by various factors, including a low threshold of inflammation. The reason? During the cyclical phases of non-REM and REM sleep, the body modulates the production of inflammatory cytokines and sympathetic nervous system activity in order to promote night-time recovery and prepare the body for daily activities. Its alteration, in the medium to long term, is however capable of remodelling pain pathways, inducing a state of sensitisation of the central nervous system.

Insomnia affects around 13.4 million Italians, mostly women. It must always be remembered that the picture must be defined according to the type of sleep disorder: it ranges from difficulty falling asleep to difficulties in maintaining sleep or early awakenings. According to the International Classification of Sleep Disorders, and the Diagnostic and Statistical Manual of Mental Disorders, insomnia becomes chronic when the patient complains of sleep difficulties at least three nights a week for a period of three consecutive months, despite adequate opportunities to sleep and is not better explained by another sleep-wake disorder, is not attributable to the physiological effects of a substance, and is not explained by a co-existing mental or medical condition. Chronic insomnia (an estimated 6 per cent of the population) impacts the subject's physical and social sphere. "It is a multifactorial phenomenon linked to stress, psychiatric disorders and comorbidities," indicates Luigi Ferini-Strambi, Chief of the Centre for Sleep Medicine and Full Professor of Neurology at the Faculty of Psychology of the Vita-Salute San Raffaele University in Milan. This increases the risk of developing disorders, including depression, anxiety, alcohol abuse, suicide risk, dementia and stroke, cardiovascular diseases and metabolic disorders, such as obesity and diabetes'. In addition, it makes one more fragile in the face of viruses. Even when young.