NEW YORK (Reuters Health) - People who exercise regularly appear to be less likely than couch potatoes to catch colds, US researchers report.

"Our research provides evidence that being active may actually reduce the number of colds people get in a year," lead author Dr. Charles E. Matthews of the University of South Carolina in Columbia told Reuters Health.

Given that colds are a leading cause of visits to the doctor and missed work days, Matthews added that employers might do well to encourage their workers to get off their duffs on a regular basis.

"While getting a cold is generally a minor nuisance for the individual, the wider public health implications are that being active may also reduce healthcare costs and increase productivity in the workplace by reducing the number of individuals getting a cold," he said.

Matthews and his colleagues obtained their findings from surveys of 547 healthy adults, administered at regular intervals over the course of a year. During the study period, the participants noted how many colds they had experienced, and how often they engaged in moderate physical activity.

For the purposes of the investigation, exercise considered moderate or vigorous included anything that people engaged in during their daily lives that was more strenuous than a walk, including household, occupational and leisure activities.

The average adult develops between two and five colds each year. However, the investigators report in the August issue of Medicine & Science in Sports & Exercise, people who reported being the most active had 25% fewer colds over the course of a year, relative to those who were the least active.

In an interview with Reuters Health, Matthew explained that previous studies have suggested that extremely low or high levels of activity can have negative effects on the immune system, thereby increasing the risk of developing colds. For example, he noted, people who run a marathon appear to have a significantly higher risk of a cold during the week after the race than non-runners.

In contrast, he added, "moderate levels of activity have been hypothesized to be associated with enhanced immune function, and our data--indicating a reduced risk for infection--are consistent with this hypothesis."

SOURCE: Medicine & Science in Sports & Exercise 2002;34:1242-1248.

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