Read more: 鈥�Immune retune: Recharging your body鈥檚 natural defences鈥�
It can be hard to motivate yourself to exercise, but now there is yet another reason to do so: even short bursts of exercise give your immune system a temporary boost.
When 500 adults were tracked for 12 weeks, those who were the most physically active 鈥� five sessions or more of aerobic exercise a week 鈥� spent nearly half the number of days sick with an upper respiratory tract infection such as a cold or tonsillitis ().
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As your heart gets pumping, immune cells usually stuck in the blood vessel walls are washed into the circulation where they can do their stuff, says Mike Gleeson, an immunologist at Loughborough University in the UK. Levels of these cells in the blood double during exercise, upping the immune system鈥檚 ability to respond to pathogens, says Gleeson. 鈥淓xercise increases immunosurveillance.鈥�
It is possible to overdo it, but you would have to be extremely dedicated. Last year, Gleeson鈥檚 team looked at how many colds athletes got compared with people who just kept fit in the conventional sense. Those who trained for 11 hours or more a week got more infections than those who worked out for between 3 and 6 hours per week ().
鈥淎thletes get more colds than those of us who just keep conventionally fit鈥�
Too much exercise has a similar effect to stress, raising levels of stress hormones such as cortisol that alter the functioning of immune cells (see 鈥淭ake a deep breath鈥�). 鈥淓ven though there鈥檚 an increase in cells, their function is depressed,鈥� says Gleeson.
He recommends exercising little and often, for no more than 2 hours at a stretch: 鈥淩estrict yourself to moderate exercise such as jogging or swimming.鈥�