Researchers from the Fred Hutchinson Cancer Research Center in Seattle conducted a study of the effects of regular exercise on breast cancer in post-menopausal women. Half of the 115 women involved in the study were put on a program in which they exercised moderately for 45 minutes a day, five times a week. The other group did not engage in exercise, but participated in a weekly stretching class for the duration of the yearlong study.
The researchers found that the women in the non-exercise group suffered from twice as many colds as those who did exercise. The protection against colds among the exercise participants was greatest during the last three months of the trial, during which the non-exercisers had three times the risk of catching a cold.
The effects of exercise on the immune system were seen in the active group despite the fact that they managed just 30 minutes of exercise a day, on average. The researchers said previous studies had shown that exercising perhaps increases levels of infection-fighting white blood cells (leukocytes) in the body, which could influence the risk of catching colds.
"The enhanced immunity was strongest in the final quarter of the year-long exercise intervention," said Dr. Cornelia Ulrich, the study's lead author. "This suggests that when it comes to preventing colds, it's really important to stick with exercise long-term.
"In everybody this level of aerobic exercise has been recommended for a number of health outcomes. The women also lost a bit of weight and fresh air could go some way to helping strengthen the immune system," Ulrich said.
Natural health advocate Mike Adams, author of "Conquering the Common Cold," said physical exercise helps prevent colds by boosting circulation, moving lymph and oxygenating the body to help support the immune system.
"The key is finding the right balance," Adams said. "Too much exercise can leave you exhausted and vulnerable to infection, and too little exercise doesn't produce any real benefits. The right amount seems to be 30 to 45 minutes per day, at moderate intensity."