Frequent Aerobic Exercisers Get Fewer Colds

There's been lots of research over the years concluding that physically active people are less likely to have serious conditions, such as heart disease. Now, a new study indicates that those who engage in frequent aerobic exercise are also less likely to catch cold or have other respiratory symptoms.

Some 1,000 participants in the study filled out a daily diary of their exercise, and then the numbers were crunched by researchers led by David Nieman of Appalachian State University in North Carolina.

"We found that the most important lifestyle factor in predicting the number of sick days during the winter and fall was the amount of physical activity," he said in a telephone interview.

Specifically, aerobic physical activity, bouts of 20 minutes or more, enough to increase the heart rate and break a sweat.

"People [who] put in those bouts, five days a week during the 12-week period, had more than a 40-percent reduction in sick days."

The reduction factored in other data, such as study participants' diet, weight, education, and gender.

Five weekly aerobic sessions of about 20 minutes each seemed to produce the best results. Those who exercised less frequently were more likely to catch cold.

Nieman says the explanation comes from what happens to certain white blood cells [Neutrophils and natural killer cells] when the body kicks into exercise mode: these immune cells start roaming the blood stream, looking for invaders, such as the viruses that cause colds and other respiratory infections.

"Most immunologists interpret this as what they call improved immunosurveillance, or the ability of the immune system to detect and then engage pathogens and destroy them," Nieman explained.

The so-called common cold is one of the most frequent illnesses in many parts of the world. According to one study, the economic burden is estimated at $40 billion a year in the U.S. alone.

David Nieman's study is reported in the British Journal of Sports Medicine.