2023-10-22 06:00:00
Regularly incriminated by victims of colds, tonsillitis and other winter ailments, does the cold really make us sick? According to specialists, while the drop in low temperatures cannot cause illness on its own, it contributes to weakening our defenses.
“Doctor, I’m sick because I caught a cold.” Doctor Patricia Lefebure, general practitioner in Limay (Yvelines), hears this sentence every day.
“People tell me: ‘I’m sick because I wasn’t dressed enough’ or ‘I went out with wet hair yesterday’,” she explains.
“I explain to them that it’s not the fact of being cold, but that you have to be in contact with a germ, a bacteria or generally a virus, to be sick. We could be completely naked at the North Pole, we would not be sick, we would have died of cold but not sick,” jokes the woman who last June became president of the Federation of Doctors of France (FMF).
At the moment, she is mainly seeing cases of nasopharyngitis, bronchitis, Covid and, for the past two weeks, RSV, the virus responsible for the majority of bronchiolitis. On the other hand, no flu yet.
“Temperature affects the mucous membranes”
Flu, RSV, Covid, rhinovirus… We are in constant contact with viruses, all our lives, even more so when we take public transport or when we have children at school. Most of the time, we defend ourselves by producing antibodies. On the other hand, when temperatures drop, this mechanism is disrupted:
“The cold snap can somehow stun the immune defenses and at that moment, we allow the virus with which we are in contact to develop,” explains Doctor Lefebure.
Stéphane Paul, professor of immunology at Saint-Étienne University Hospital, confirms: “Scientific data show that temperature affects the mucous membranes, and in particular the nasopharyngeal sphere. At the level of these mucous membranes, several components impact the immune response. first, the microbiota that we have in the nose and lungs in particular. The lower the temperature, the less effective it is.”
When temperatures drop, this microbiota is in less good shape to help the body fight viruses.
With the cold, the mucous membrane of the nose functions less well. “It is less impermeable to pathogens. This will facilitate the entry of viruses,” explains the immunologist who is also a member of the Technical Commission for Vaccinations of the High Authority for Health.
“Higher risk of infection”
It is in a way our adaptation to the cold which will increase our vulnerability, as Professor Bruno Lina explains to us: “When we are in a period of extreme cold, our respiratory haven suffers, because it must warm up the air to be able to bring it to the right temperature and carry out gas exchanges in the pulmonary alveoli.”
“This heating of the air occurs through the transfer of water, which will dry out the mucous membranes and weaken the respiratory mucus which is a protective structure. The risk of infection is therefore higher because non-specific barriers do not work. no longer very good”, estimates the virologist, director of the National Reference Center for Respiratory Viruses in Lyon.
Specialists also mention another element of explanation: the slow functioning of our immune system in the presence of cold. “We have a lot of data on this for 30 years. We know, for example, that macrophage cells, whose role is to eat bacteria to eliminate them, tend to migrate less well when it is cold,” explains Stéphane Paul.
“More sensitive at the start of the season”
Finally, there is an indirect element to take into consideration: the cold contributes to a change in our behavior conducive to infection. “We are more able to be indoors, next to each other, ventilation is less well respected. The carriage of the virus, either via the spit which is likely to directly enter your nasal cavity, or via surfaces that you will then touch, is favored by the cold”, notes Vincent Enouf, deputy head of the National Reference Center for Respiratory Viruses at the Pasteur Institute.
However, there is still good news according to immunologist Stéphane Paul: this vulnerability to low temperatures would gradually fade, after an adaptation phase. “The data in the literature show that the body manages to get used to these cold conditions after 3, 4 or even 6 weeks in animal models, then it starts to work better again. This is why at the start of the season, we are more sensitive. This is true in the nose, but also in the intestine with gastros”.
“Probiotics, vitamins D and C”
As for solutions to protect against this easier entry of viruses and bacteria when temperatures drop, for Patricia Lefebure, there is no need to self-medicate:
“The body is made for that, we have to let it adapt, we stay in a temperate country,” she explains.
Stéphane Paul talks about the benefit of strengthening your immune system at the start of the season. “This can involve probiotics to strengthen the microbiota, favoring live bacteria which promote interactions between them,” he explains. The specialist also mentions the role of vitamin D and vitamin C, “because they tend to stimulate the functioning of the epithelium, that is to say the cell membrane which acts as a barrier against the outside” .
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