Impact of running on immunity
It appears that moderate exercise increases resistance to disease and infections; but that heavy training and racing weakens the immune system. Mild exercise raises the body temperature and stimulates production of white blood cells and so helps the body to fight infection.[i] In general, the higher level of fitness in runners reduces their overall rates of infection and disease.
However, there is considerable evidence that susceptibility to infection is increased by running marathons. For example, 13 per cent of the runners who completed the Los Angeles Marathon in 1987 became ill during the week after the race, compared to just 2 per cent of the control group of runners who didn’t participate in the event.[ii] It is not clear why runners are especially prone to respiratory infections such as sore throats and bronchial infections. It may be to do with the trauma to the throat linings of hard breathing while running. But there also appears to be a lowering of the effectiveness of the immune system generally in runners who are training hard, which contributes to this phenomenon.
My own experience is that respiratory infections are the main constraint on my ability to train hard enough to improve my performance. So for some runners, finding ways to reduce the likelihood of infections is especially important for improving our running, as well as general quality of life.
The main approaches to reducing infection are:
- ensure you have a good diet – you need to eat a wide selection of fresh fruit and vegetables, and get enough essential minerals (especially zinc);
- avoid swings in your blood sugar level, which appear to cause reduced immunity; in general you should eat low glycaemic carbohydrates (except when you want a sugar boost, such as immediately before or after a long run). And if you eat a snack that is high in carbohydrates (e.g. fruit) make sure you have some protein with it (e.g. a handful of nuts);
- take a vitamin C supplement: take about 2,000mg to 4,000mg a day when you are training heavily; and increase this to 1,000mg an hour (really – this is not a typo!) if you feel as if you are getting ill; although there is an upper limit beyond which increases in Vitamin C don’t help, it won’t do you any harm (apart from the expense);
- take a zinc supplement; however, unlike Vitamin C, it is dangerous to take excessive doses of zinc, so restrict yourself to 100mg a day;
- some runners claim that Echinacea extracts, available in chemists and health food shops, improve their immune system; I don’t believe it, but maybe it will work for you;
- avoid rapid increases in your training load; build up slowly, increasing by not more than 10% or 2 miles a week (whichever is the greater);
- don’t do two hard training sessions on consecutive days;
- avoid crowded buses, trains and tubes if possible, for example by running, cycling or walking to work; and wash your hands regularly to avoid infection;
- make sure you get enough sleep.
My own experience is that I was able to greatly reduce my incidence of upper respiratory tract infection by a combination of large doses of vitamin C, eating a good combination of carbohydrate and protein after long runs, and obsessive hand-washing in times of low immunity (in the 24 hours after a long run.)
Infection while tapering
As we shall see in Chapter 11, long distance runners generally reduce their training mileage immediately before a big race. This is called “tapering”.
Many runners are especially susceptible to infections when they are tapering. This phenomenon has not been researched, but paradoxically it appears to be a response to the reduced stress the body is under as you cut back your training load. This may be the same effect as the tendency to fall ill on the first few days of a holiday. It may also be that you begin tapering just after the peak of your training load, so any infection is a delayed response to earlier stresses your body was under. The effect is especially disruptive, because the runner becomes ill just at the time at which they want to conserve their energy and health.
To avoid illness in the tapering phase, you should follow the guidelines above for avoiding infection. But you should also continue to train during the tapering phase, and maintain high levels of effort, albeit over smaller distances, to prevent the body from “shutting down”.
Running with an infection
Runners often want to know whether it is safe to continue running if they have a sore throat, cold or a cough.
In general, it is safe to continue running if you feel like it, provided that your body temperature is normal and that all the symptoms are all from the neck upwards. You should not run if your temperature or resting heart rate are elevated, you have aching muscles or sore joints, diarrhoea, or if you have a chest infection. If your symptoms are a nothing more than a sore throat or a runny nose, you can go out for an easy run. If your head starts to pound or if you don’t feel well, turn round and go home.
My experience is that it is better to rest if you don’t feel well. You are likely to lose less running overall if you let your body recover and get back to full strength quickly than if you try to train through an infection, and prolong the time it takes you to recover. If you do run with a cold, take it easy. Don’t do a hard track session, or a long run.
Exercising while you are infected with a virus can be especially dangerous, since it can lead to an infection of the heart called myocarditis. You should not exercise at all if you have symptoms of a viral infection (such as fever, aching muscles or sore joints), and you should avoid vigorous exercise for a fortnight after your body temperature returns to normal. You should not exercise at all if your resting heart rate remains elevated. Myocarditis can cause severe damage to your heart and is sometimes fatal. If you might have a viral infection, don’t even think about running.
[i] Hanson, P.G., & D. K. Flaherty (1981) “Immunological responses to training in conditioned runners.” Clinical Sciences 60, 225-228
[ii] Nieman DC, Johanssen LM, Lee JW, Arabatzis K. “Infectious Episodes in Runners Before and After the Los Angeles Marathon”, Journal of Sports Medicine and Physical Fitness, vol. 30, 1990, 316-328.