Some time ago, we sent an article about "illness comes like a mountain, illness goes like a silk", many small partners said, "a thousand years of sayings, but also personal feelings, in the past A half-understanding, now finally seconds to understand."
Many people also asked: "I have also heard a saying: often colds are beneficial to health, and the probability of getting a serious illness is small; people who rarely get sick are seriously ill." Is this statement true? ”
This statement, which the grumpy little doctor also often hears, has two meanings:
Often colds, in the end can you "exercise people's immunity" and help you not get seriously ill?
People who rarely have a cold, is it really a serious illness as soon as they get sick?
Next, let's solve the first problem -
The answer is: no!
The saying that "frequent colds exercise the immune system" may come from an academic hypothesis , the "hygiene hypothesis."
This is what the epidemiologist Dr. Strachan proposed in 1989, mainly referring to:
If the living environment in early childhood is too clean and there is no opportunity to contact some microorganisms, it may lead to defects in the regulation of the immune system, which increases the incidence of chronic inflammation such as asthma and allergies.
Conversely, if the child's living environment is "dirty", the immune system can be more knowledgeable, in order to better operate, and will not make a fuss about some "substances that would not otherwise cause an immune response".
Image source: Stand Cool Helo
Key: The microbes mentioned in the "hygiene hypothesis" mainly refer to bacteria that coexist with humans [1,2].
The point of the matter: it's bacteria, not viruses!
In fact, colds are mainly caused by viral infections. The most common are rhinovirus, respiratory syncytial virus, parainfluenza virus, adenovirus, human coronavirus, etc.
We refer to it as "cold virus" in this article.
When the virus infects the human body, these two main things happen:
1. Activates the immune process against the cold virus
When the virus reaches the nasal mucosa and enters the cells, the immune system is activated, producing antibodies, immune cells, inflammatory factors, etc., attacking and destroying the virus, which is what causes your cold symptoms.
For example, the inflammatory response after viral infection stimulates the nasal mucosa to swell, the cells to expand, and secrete a large amount of mucus to form a nasal discharge to block the invasion of the virus.
For example, the front-line force of the immune system, natural killer cells (NK cells), can destroy the virus hidden in the cells, but kill 1,000 enemies and damage 800, and normal cells will also be killed, which will induce redness and swelling of the throat.
Immune cells and antibodies that kill red eye, etc., may sometimes be hostile to me and attack normal cells.
A small number of people develop viral myocarditis after a cold [3].
2. Cross immunity can be formed
There are many types of cold viruses. Infected with a certain type of cold virus, and then encounter a similar virus, the immune system can recognize it and quickly begin to organize the fight. This is medically called "cross immunity."
(Source: self-drawn)
Recent studies have found that after being infected with the "human coronavirus" (a class of cold viruses), the immunity obtained also has a defensive effect on the new coronavirus [4]. This is the cross-immunity of the common "human coronavirus" and the new coronavirus.
However, observational studies have found that viral infections in early childhood do not achieve this protective effect [2].
That said, the hygiene hypothesis may not support the claim that frequent colds exercise the immune system. People who often have colds may not be able to "avoid serious diseases".
Read more medical codes: if your child has a cold, just take some anti-inflammatory drugs?
Poke the video to see the truth
The article is not finished yet, continue to read to the end oh ~
Seeing this, you may ask: Why do some people often catch colds, while others do not catch a cold once in several years?
This is mainly related to two factors.
1. Genetic factors
Certain genes determine whether we are susceptible to cold viruses or not, and also affect the severity of post-infection.
For example, a gene called IFH1, if mutated and leads to loss of function, can cause immunodeficiency, making children extremely susceptible to respiratory syncytial virus, rhinovirus and other viruses [5].
But don't worry, this genetic variant is very rare.
2. Lifestyle habits
Many factors in daily life affect our susceptibility to cold viruses, such as sleep, stress states, diet, exercise habits, etc.
A study in the United States found that people who slept less than 7 hours were 2.94 times more likely to develop a cold than those who slept more than 8 hours [6].
Conversely, staying active, eating a healthy diet, etc., can reduce the risk of catching a cold.
The study found that regular moderate-intensity exercise may achieve the effect of preventing colds compared with people who do not exercise, reduce the risk of colds by about 27%, and shorten the course of colds by 3.5 days [7].
3. Environmental factors
Scientists in Sweden, the United States, Israel and other countries surveyed 210 healthy twins aged 8 to 82 responding to the flu vaccine and found that 58% of them were almost entirely affected by environmental factors. And, the older they get, the more pronounced the differences between their immune systems [8].
This may illustrate two points:
First, pathogens in the living environment can affect the risk of infection;
Second, people's immunity is also affected by environmental factors.
Let's answer to the last question -
In life, you may often hear people say that who has not caught a cold in their whole life, how to suddenly find cancer. Is this the truth?
A German study showed that people who had an average cold of 3 or more times a year did not differ in cancer risk compared to those who did not develop a common cold in 5 years [9].
From the clinical experience, the reason why some people usually rarely have a cold, but suddenly get a serious illness, mainly because he ignores mild symptoms and does not often go to the hospital.
People who often have colds are generally more sensitive to the symptoms of the disease, and they often go to the hospital for examination, which is easier to detect the disease at an early stage.
Many people who have never had a cold may have completely ignored the slight cough, fever and other symptoms, and the slight performance of other bodies is not too concerned. Once the symptoms reach a level that cannot be ignored, there is a high probability that they are serious diseases. It's easy to give people a sense of impact.
Summary
Frequent colds may give you cross-immunity to certain diseases, and it can also urge you to go to the hospital for more examinations, but it does not "exercise" your immune system.
And the frequent cold itself may also be a manifestation of your lack of resistance to the cold virus.
In a word, no matter how many colds there are, the annual physical examination can not be forgotten!
Don't forget to share this article, you can help more friends Oh~
bibliography
[1] Pfefferle PI, Keber CU, Cohen RM, et al. The Hygiene Hypothesis - Learning From but Not Living in the Past. Front Immunol. 2021;12:635935.
[2] Rook GA. Review series on helminths, immune modulation and the hygiene hypothesis: the broader implications of the hygiene hypothesis. Immunology. 2009;126(1):3-11.
[3] Dennert R, Crijns HJ, Heymans S. Acute viral myocarditis. Eur Heart J. 2008; 29(17): 2073-2082.
[4] Mateus J, Grifoni A, Tarke A, et al. Selective and cross-reactive SARS-CoV-2 T cell epitopes in unexposed humans. Science. 2020;370(6512):89-94.
[5] Asgari S, Schlapbach LJ, Anchisi S, et al. Severe viral respiratory infections in children with IFIH1 loss-of-function mutations. Proc Natl Acad Sci U S A. 2017;114(31):8342-8347.
[6] Cohen S, Doyle WJ, Alper CM, Janicki-Deverts D, Turner RB. Sleep habits and susceptibility to the common cold. Arch Intern Med. 2009;169(1):62-67.
[7] Lee HK, Hwang IH, Kim SY, Pyo SY. The effect of exercise on prevention of the common cold: a meta-analysis of randomized controlled trial studies. Korean J Fam Med. 2014;35(3):119-126.
[8] Brodin P, Jojic V, Gao T, et al. Variation in the human immune system is largely driven by non-heritable influences. Cell. 2015;160(1-2):37-47.
[9] Abel U, Becker N, Angerer R,et al. Common infections in the history of cancer patients and controls. J Cancer Res Clin Oncol. 1991;117(4):339-44.
Author: Jiang Yongyuan | Editors: Zhang Jie, Zhang Li, Zhang Liang
Typesetting: Han Ningning | Proofreader: Wu Yihe
Operations: Li Yongmin | Coordinator: Wu Wei
*The content of this article is a popularization of health knowledge and cannot be used as a specific diagnosis and treatment recommendation, nor is it a substitute for face-to-face consultation by a practicing physician, for reference only.
*The copyright of this article belongs to Tencent Medical Code, unauthorized media reprinting is prohibited, and illegal reprinting will be investigated for legal responsibility according to law. Individuals are welcome to forward to the circle of friends.
* Welcome to WeChat search and pay attention to the public account "Tencent Medical Code" to get more health science knowledge.