Why do physically trained athletes catch a cold?
The relationship between exercise and susceptibility to cold has been demonstrated scientifically. Compared to people who don’t exercise at all, those who exercise moderately don’t catch a cold easily. It is true that if you strengthen your body, you won’t catch a cold. Then, what happens if you increase the amount or intensity of exercise further? You will become more susceptible to colds than those who don’t exercise at all, too much can be as bad as too little. Regularly trained athletes often do too much exercise, and they catch a cold more easily than general people.
Susceptibility and resistance to colds
In most cases, colds are infectious disease caused by viruses. When a cold virus invades the mucosal membrane of the nose or throat and propagates there, inflammation occurs and we develop a cold. Immunity prevents cold viruses from invading the mucosal membrane and then attacks and eliminates the invading viruses. We don’t catch a cold if we have a strong immune system, whereas we easily catch a cold when our immunity weakens. Moderate exercise improves immunity and makes us less susceptible to cold, whereas excessive exercise decreases immunity and makes us more vulnerable to cold. An immunity substance (secretory immunoglobulin A) in saliva prevents cold viruses from invading the mucosal membrane. This secretory immunoglobulin A is shown to decrease significantly if you participate in a 42-km marathon or intense college athletic club camp for example. Athletes have decreased immune function as their level of exercise is often excessive. This is why they easily catch a cold and become ill. Athletes are often in the condition of chronic fatigue called overtraining syndrome as a consequence of excessive training. Their immune function also decreases in such a condition.
How to do exercise to improve immunity
How much exercise is moderate exercise to improve immunity? In our study, we measured the amount of daily exercise in elderly people using a pedometer and evaluated its relationship with immunity. The level of the immunity substance (secretory immunoglobulin A) in saliva was high in elderly people who walked about 7,000 steps daily. We asked elderly people who weren't in the habit of exercising to continue with an exercise program twice a week (60 to 90 minutes per program, mild resistance training and aerobic exercise) and found that their level of secretory immunoglobulin A increased. Other elderly people who continued 30 minutes walking five days a week also showed an increased level of secretory immunoglobulin A.
Why does exercise change immunity?
The human being is said to comprise about 60 trillion cells. The internal environment of the body where individual cells survive is maintained at a constant temperature and pH (homeostasis). When we do exercise, events such as energy consumption, production of fatigue substances, and increase in body temperature occur, resulting in a large change in the internal environment. This change in the internal environment is called stress. Besides psychological stress, there are various types of stress including exercise. The autonomic nervous system, endocrine system, and immune system respond to stress to maintain the homeostasis of the internal environment. Moderate stress stimulates these systems and improves their functions, whereas excessive stress taxes these functions, resulting in the loss of physical health. As exercise is one type of stress, we will be able to train our immunity and improve the ability to maintain our health through moderate exercise.
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