MONDAY, November 1 (Health.com) — Regular exercise can improve your mood, help you lose weight, and add years to your life. Still need another reason to hit the gym? A new study suggests that working out regularly helps ward off colds and flu.
In the study, researchers followed a group of about 1,000 adults of all ages for 12 weeks during the winter and fall of 2008. During that time, people who logged at least 20 minutes of moderate aerobic exercise—such as jogging, biking, or swimming—on five or more days per week were sick with cold or flu symptoms for just five days, on average, compared to about 8.5 days among people who exercised one day per week or less.
What's more, regular exercisers tended to have milder symptoms when they were ill. Compared to the people who barely exercised, those who worked out frequently rated their symptoms about 40% less severe overall, according to the study, which was published in the British Journal of Sports Medicine. (Symptom severity was gauged with a standard questionnaire.)
Exercise is thought to boost the circulation of the virus-fighting white blood cells known as natural killer cells—the "Marine Corps and Army of the immune system," says the lead author of the study, David Nieman, a professor of health, leisure, and exercise science at Appalachian State University, in Boone, N.C. "Exercise gets these cells out…to deal with the enemy."
The increased immune activity brought on by exercise only lasts for about three hours, but the cumulative effect seems to keep disciplined exercisers healthier than most. "As the days add up, it adds up to improved protection [from] the viruses that can make you sick," Nieman says.
Endorphins may also play a role, says Len Horovitz, MD, a pulmonary specialist at Lenox Hill Hospital, in New York City. These feel-good neurotransmitters—the source of the so-called runner's high—have "positive effects on the immune system, so it's not surprising there's a spike in immune cells," says Dr. Horovitz, who was not involved in the study.
It's also possible that people who exercise frequently tend to lead healthy lifestyles in general, and are therefore less likely than couch potatoes to get sick.
Nieman and his colleagues measured a host of factors besides exercise that could potentially affect a person's susceptibility to cold or flu, including age, gender, diet, stress levels, marital status, smoking, and educational attainment. Of all of these, physical activity was most closely linked to the number of days a person spent sick, although some characteristics, such as being married and eating a lot of fruit, seemed to help protect against colds and flu as well.
"You can't do much about your age, and you can't do much about your gender. Here's something you can really do," Nieman says. "Exercise is the most powerful weapon that an individual has in their hand to reduce illness days."