We all know that exercise is good for us. It tones the body and improves cardiovascular function. Researchers have also found that exercise may even boost your immune function–unless you exercise too intensely.
Swedish researchers tested rats to see how different levels of exercise affected the immune system. The rats were kept in separate cages. One group had cages without exercise wheels. Cages of the other rats had exercise wheels. Researchers tracked how much and how far each rat ran.
Those in the rat race followed a running schedule. They ran every day for either five or 11 weeks straight. Or they started out running every day for five weeks and then ran only four days a week for the final six weeks. At the end of the study period, the rats were injected with cancer cells that congregate in the lungs. Researchers then checked the rats’ lungs to see how well their immune systems had managed to clear the cancer cells.
All of the running groups showed better immune function than the sedentary group. The rats that ran every day for 11 weeks showed the poorest clearance of cancer cells of all the running groups. The researchers also grouped the rats by how far they ran each day. All of the runners showed better immune function than the sedentary group. And the rats that ran more often showed better immune function than the rats that ran the least.
The authors conclude that exercise–at least in rats–does seem to boost immune function. But the study also shows that doing too much training for too long seems to erode the benefits. It’s hard to make conclusions for humans based on animal studies. But the authors say that their results suggest there should be more research on “the important role of adequate rest in prevention and treatment of overtraining in humans.”