Study leader Dr Cornelia Ulrich, Fred Hutchinson Cancer Research Center, said: "The enhanced immunity was strongest in the final quarter of the year-long exercise intervention."

"This suggests that when it comes to preventing colds, it's really important to stick with exercise long term," she added.

"In everybody this level of aerobic exercise has been recommended for a number of health outcomes. The women also lost a bit of weight and fresh air could go some way to helping strengthen the immune system."

"It's important to bear in mind that this is the first study to show this and ideally we would like a much larger trial."

The Common Cold Centre at the University of Cardiff say they have always supported the idea of exercise as a way of improving health so the results of this study were pleasing, exercise increased levels of leucocytes, boosting the immune systems ability to fight off infection a perfectly reasonable piece evidence.

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