Nov. 12, 1998 A new University of Colorado at Boulder study suggests that choosing to exercise regularly in moderation may help guard against the negative effects of stress on the body's immune system.
People who exercise regularly are less likely to get sick after stressful situations than people who don't exercise, said Assistant Professor Monika Fleshner of the department of kinesiology and applied physiology at CU-Boulder. Doctors know exposure to mental or physical stress can increase susceptibility to and severity of disease.
Fleshner's study measured the effect of stress on immune responses in laboratory rats that could either choose to exercise or remain sedentary. Rats that began running on a wheel for four weeks prior to exposure to stress were protected against the suppressive effect of stress exposure on immune response.
But rats that either began running on the day of stress or that remained sedentary suffered the negative effects of stress exposure, she said. Fleshner will present her findings Nov. 10 at the annual meeting of the Society for Neurosciences, to be held in Los Angeles.
Although Fleshner's study was done with animals, it could have important implications for people. "If a person who regularly exercises in moderation is under stress, that person is less likely to get sick than someone who has been sedentary and faces the same challenge," she said.
"This suggests that what we need to do is keep our exercise programs going and keep moderate, regular and voluntary exercise going," she said. "Then when we are hit with our deadlines or stress at work, marital stress or loss of a loved one, we may be able to better buffer those negative effects of stress on the immune system."
To reap the benefits of exercise, the exercise program needs to begin before the stressful situation, she said. A person who begins exercising on the day the stress begins will not prevent the negative effects of stress on the immune system.
For the study, six groups containing 10 adult male rats each were assigned to one of the following groups: wheel running before and after stress; wheel-running only after stress; no wheel running and stress; or one of three no-stress control groups, Fleshner said.
The animals were injected with a foreign protein called keyhole limpet hemocyanin, or KLH, so the status of their immune systems could be assessed. They were injected immediately before exposure to a 90-minute laboratory stress that is known to suppress immune response. The injection stimulates an immune response similar to that produced by a vaccination, she said.
The level of the immune response was determined by measuring antibodies in the blood against KLH. Blood samples were taken once a week for five weeks after the KLH injection. The results revealed that only the rats that ran before and after the stress were protected against the suppressive effect of stress on the antibody response to KLH.
Rats that were sedentary or began running on the day of stress exposure had suppressed antibody responses to KLH, Fleshner said.
The study was a logical extension of her previous experiments on rats and stress, which found forced exercise is stressful and can actually suppress several measures of immune function. But if individual rats are able to exert control over the type, intensity and duration of their physical activity, exercise can benefit the immune system, she said.
The future goal of her research is to understand the neuro-hormonal adaptations produced by exercise that protect against the negative effects of stress, Fleshner said.
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