A regular brisk walk can boost the body's immune system, the professor found

Taking a regular brisk walk can help you fend off winter bugs, but strenuous exercise such as long-distance running can make you more susceptible to colds and flu.

Those are the findings of Loughborough University expert Professor Mike Gleeson, who said couch potatoes who take little exercise are also likely to suffer more cold-like infections.

Professor Gleeson said moderate exercise such as a brisk daily walk enhances the action of the body’s natural killer cells, which help fight off viruses.

The academic, speaking at the Association for Science Education conference, said: “NK cells recognise viral-infected cells as foreign invaders and force them to commit suicide.

“During moderate exercise the activity of NK cells is enhanced, whereas stressful endurance activities such as marathons can turn down NK cell activity. These changes are tightly regulated by stress hormones and other immune cells.”

Speaking on behalf of the Society for General Microbiology and the British Society for Immunology, he told the conference that upper- respiratory tract infections are acute infections that affect the nose, throat and sinuses, and include the common cold, tonsillitis, sinusitis and flu.

Viruses that circulate in the environment usually cause URTIs. While we are constantly exposed to these viruses, it is the status of our immune system that determines whether we succumb to infection or not.

Exercise can have both a positive and negative effect on immune function, combined with genetics and other external factors like stress, poor nutrition and lack of sleep. Collectively these factors determine an individual’s susceptibility to infection, he said.

Professor Gleeson explained why the exercise is a factor in catching bugs. “If you have a tendency to be a couch potato then you probably have an average risk of catching an infection – typically two to three URTIs a year.

“Research shows that those undertaking regular moderate exercise, for example, a daily brisk walk, can reduce their chance of catching a respiratory infection, such as a cold, by up to almost a third,” he added.

The cumulative effect of exercise leads to a long-term improvement in immunity.

Professor Gleeson said: “Conversely, in periods following prolonged strenuous exercise, the likelihood of an individual becoming ill actually increases. In the weeks following a marathon, studies have reported a two- to six-fold increase in the risk of developing an upper respiratory infection.

“The heavy training loads of endurance athletes make them more susceptible to URTIs and this is an issue for them as infections can mean missing training sessions or underperforming in competitions.”

Regular walkers can be cheered by the professor’s findings which, he said, provided a clear message from current understanding of the link between exercise and immune function. “Moderate exercise has a positive effect on the immune system. So to keep colds at bay, a brisk daily walk should help – it’s all about finding a happy medium,” he added.