First author of the study, Dr. Wojciech Feleszko, a paediatrician and professor at the Medical University of Warsaw, said: “We want to send this message to the world, make parents and paediatricians aware of it. They should encourage their charges to engage in daily physical activity.

“As a paediatrician, I observe a feature that strongly distinguishes us from many other nations: that infections in children cause a lot of fear and anxiety in Polish parents. In Western Europe, especially in Norway, Finland and the UK, it is normal that kids run around in shorts even in autumn, go to kindergarten with a runny nose, etc. In Poland it is the opposite - children are overly insulated and overheated.

“I was interested in whether physical activity could be a factor that makes children get sick less. Such reports concerning adults have already appeared in world literature. I collaborated with doctoral candidate Katarzyna Otrzyżek-Przeździecka, a kindergarten physiotherapist, to check whether children who move less get sick more.”

The experiment, the results of which were recently published in Pediatric Research, involved 104 children aged 4-7 years.

The scientists combined two different research methods: firstly, preschoolers wore wristbands to monitor their activity level during the day, which accurately reported the number of steps they took and the level of movement (this part of the study was carried out in collaboration with the University of Physical Education in Poznań); secondly, the parents of young participants filled out questionnaires in which they specified the number of upper respiratory tract infections their charges had in the given period.

The authors took into account factors that could affect the results, such as vaccinations, chronic diseases, having siblings, exposure to cigarette smoke and pet dander.

It turned out that the more active children got sick much less often, and they recovered from the infection faster. Increasing the average daily number of steps by 1,000 reduced the number of days with symptoms of infection by four days, and the severity of these symptoms was inversely related to the level of physical activity.

In addition, the researchers calculated that children who played sports for three or more hours per week developed upper respiratory tract infections less often than those who did not exercise regularly.

Feleszko said: “In this type of research, when two different factors are assessed, it is always difficult to say which of them is the cause and which is the effect. One might just as well assume that children move less because they often get sick and their parents keep them at home, do not they take them for walks, etc.

“To determine this, we conducted a delayed effect analysis.”

The study group was divided into two subgroups: the one that moved more (i.e. took more steps during the day) and the one that moved less. The first walked approx. 9,000 steps during the day, the second about 5,000 steps (which, as the professor emphasizes, is still a very good result that most parents could envy their children). Then, preschoolers from both groups were compared with questionnaires completed by their parents, and it quickly turned out that the level of infections was very different in the two groups. Children who were more active had noticeably fewer infections and noticeably shorter periods of them: higher levels of activity at the beginning of the study were associated with fewer days with respiratory symptoms over the following weeks. Among 47 children, whose average daily number of steps was slightly more than 5,500 at the beginning, the total number of sick days in the next six weeks was 947. And among 47 children, who at the beginning reached an average of about 9,500 steps, the number of days with cold symptoms was 724.

Feleszko said: “This is the first such result obtained in a study on children. We are very happy that we have been able to demonstrate this relationship.”

It is clear that the dependency exists, but what is behind it? 

Dr. Feleszko said: “For several years, there has been talk in biology and medicine about extracellular vesicles. All cells of our body, especially epithelial cells, produce tiny vesicles into which they release various active substances, including microRNAs. When our publication was in the review process, one of the reviewers suggested that perhaps they were the cause of the described relationship, that the connection between the upper respiratory epithelial cell and muscle cells was controlled by extracellular vesicles carrying microRNAs.

“When we started to explore the topic, this hypothesis turned out to be extremely accurate.”

MicroRNA, which is a single-stranded RNA molecule measuring only 21-23 nucleotides, is a kind of 'messenger'. Although it is already detected in many diseases, scientists still do not know its exact role. It appears to be used for communication between the various cells of the body over greater distances; it is like a text message. 

Feleszko said: “In the case of our study, muscle cells stimulated by movement secrete microRNAs and thus affect the defence of epithelial cells, those that are attacked by viruses that cause common cold.

“This hypothesis fits beautifully with the findings of a very interesting American study released in December 2022, explaining why we catch cold more easily when it is cold. Everyone knows that you do not get sick from the cold, but from viruses and bacteria, but that there are undoubtedly more infections in autumn and winter. There may be various reasons for this, but the authors of the mentioned study managed to show that when it is cooler, epithelial cells secrete extracellular vesicles with substances that suppress the immune response, and thus reduce resistance to viruses.

“If you exercise and move regularly, your muscle cells secrete vesicles with contents that can affect the rest of the body, including resistance to infection, the rate of aging, etc.”

He added that greenery can also have an indirect beneficial effect on health. This phenomenon has already been described many times in scientific literature. It seems that contact with various green areas has an extremely beneficial effect on the immune system. This is certainly mediated by the sun that stimulates the production of vitamin D, but also - as scientists speculate - the diversity of the microbiome. Both of these variables affect the immune system. Frequent contact with nature can modulate the composition of the microbiome in a way that brings many benefits to the body. (PAP)

Katarzyna Czechowicz

kap/ zan/ kap/

tr. RL