Older men who exercise regularly may not only keep themselves in good shape, they may also give their immune systems a boost, new study findings show.

Physically active seniors who were injected with a protein to provoke an immune system reaction mounted an immune response similar to that seen in men half their age.

“Maintaining a physically active lifestyle may prevent or slow age-associated decline in immune function,” study author Dr. Monika Fleshner the University of Colorado at Boulder told AMN Health.

“Not only is it likely that these older physically active men are better able to fight infectious illness, but they are also probably better able to mount effective immune responses against influenza vaccinations,” she added.

The normal aging process involves a gradual decline in the immune system’s ability to respond to foreign substances. This puts older individuals at risk of infectious disease and also prevents them from effectively responding to various vaccinations.

Other researchers have reported that regular walking, cycling or other moderate exercise training may help compensate for some of the immune system changes observed in older people, but many such studies have involved laboratory tests with immune system cells rather than patients.

To further investigate, Fleshner and her team injected 46 active and sedentary men between 20 and 35 years or 60 and 79 years with KLH, a protein derivative of sea mollusks, to provoke a new immune system response.

“The immune system requires very different cellular responses when mounting a response for the first time versus for the second or third times,” Fleshner said. “Our study eliminated this added complexity, making our finding very clear to interpret.”

The active study participants said they engaged in running, cycling or some type of aerobic activity three or more times each week and had done so for more than two years; their sedentary peers said they had engaged in no regular exercise during a similar time period.

After immunizing the study participants against KLH, the researchers injected them with the same protein again three weeks later. As expected, the older men - active and sedentary - had a weaker immune system response than did their younger counterparts, the researchers report in the August issue of the Journal of Applied Physiology.

However, the physically active seniors had a stronger immune system response than did their sedentary peers. In fact, their immune response was similar to that observed among the younger men. In contrast, the physically active young men had an immune response that was generally similar to that observed among their less-active peers.

The immune response in young men “is already optimal,” Fleshner said. “There is no reason to increase an already optimal immune response, and in fact, too much immunity is as bad as too little.”

Yet, Fleshner was “quite amazed” that the older men were able to maintain an immune response “in the face of aging” that was close or similar to a young man’s immune response, she said.

Whether the physically active older men owe their increased immunity to their participation in regular exercise or to genetics, however, is unknown, Fleshner added.

SOURCE: Journal of Applied Physiology, August 2004.