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(指出) that those who engage in frequent aerobic exercise(有氧训练) are also less likely to catch cold or have other respiratory(呼吸的) symptoms.
About 1,000 participants in the study filled out a daily diary of their exercise, and then the numbers were crunched(嘎吱咀嚼，这里指分析) 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."
Specifically, aerobic physical activity, bouts(回合) of 20 minutes or more, enough to increase the heart rate and break a sweat.
"People that put in those bouts, five days a week during the 12-week period, had more than a 40-percent reduction in sick days."
Five weekly aerobic sessions(时间段) 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 when the body kicks into exercise mode: these immune cells start roaming the blood stream, looking for invaders(入侵者), such as the viruses that cause colds and other respiratory infections(传染病).
"Most immunologists(免疫学家) interpret(解释说明) this as what they call improved immunosurveillance(免疫监视), or the ability of the immune system to detect and then engage pathogens(病原体) and destroy them."
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.