Too frequent exercise may increase risk of contracting the flu during an epidemic.
Like many unfortunate people this winter I had to suffer through the flu. For me, it was easy to see a link between excessive exercise and catching the flu. I developed flu-like symptoms the very night after completing a long run and bike ride. I awoke the next morning to an unwanted flu. There has been a lot of research done on the flu’s link to exercise.
In 2008, a study entitled Is Exercise Protective Against Influenza-Associated Mortality looked at the association between physical exercise frequency and influenza-associated mortality risk of Hong Kong residents. The study found that those who exercised moderately (once per month to three times a week) showed the smallest risk of influenza mortality. People who reported exercising frequently (4 or more times per a week) showed no significantly lower risk of influenza mortality than those who reported never/seldom exercise (less than once a month). The results were statistically the same even when controlling for environmental and lifestyle factors.
The researchers explain these results through exercise’s affect on immune function and recovery. Exercise results in beneficial effects on immune function through viral clearance function, antibody titer and neuroendocrine factors. However, exercise also results in impaired immunity requiring a recovery period.
To convolute the exercise and infectious disease relationship further, a study published in 2000 found an inverse relationship between physical activity and upper respiratory tract infections in healthy, elderly people. The study, entitled The symptomology of upper respiratory tract infections and exercise in elderly people, looked as the number of days and number of independent episodes of upper respiratory tract infections in subjects from ages 66-84.
Apparently, if not contracting influenza is your number one priority this winter avoid excessive exercise. However, as the authors of the 2008 study recommend, exercise should only be limited when an influenza outbreak is present.
Please comment on this research and your personal experiences with exercise and the flu.