Lifeguard Bob Speca looks forward to spending a little less than four hours today--his 29th birthday--running in the Los Angeles Marathon. The Ventura resident has completed 17 marathons and also has several triathlons to his credit.
Nat Pisciotta, 82, of Whittier, also expects to run the race. It will be the retired mechanical engineer's 20th marathon since he started running 14 years ago.
Both runners maintain that since they started running, their health has improved and their resistance to colds has increased.
After he began distance running in the 10th grade, Speca said, his muscle tone improved, his body fat decreased and his heart rate slowed. He admits to catching occasional colds, but says they don't linger the way they did before he took up running.
People like Speca and Pisciotta who exercise regularly may be healthier than those who don't because, among other reasons, elevated body heat due to exercise may help immunize them against bacterial and viral infections, according to emerging medical evidence.
Body temperature rises as a result of exercise as well as a result of infection. There is evidence that the fever-related rise in body temperature caused by bacterial or viral infection helps fight that infection. And some researchers say there's a strong possibility that increased body heat due to exercise has the same therapeutic result.
In fact, there are a remarkable number of similarities among the physiological responses to exercise and to infection, according to University of Michigan physiologists Joseph G. Cannon and Matthew J. Kluger writing in the journal Science.
Doctors and scientists emphasize that while there is evidence that body heat from exercise helps fight infection, they are not ready to state it positively. "This is an exciting area of research," said Dr. David Heber, chief of the division of nutrition at UCLA Medical Center. "Increases in body temperature have great potential for fighting bacterial and viral infections. On the other hand, it is probably premature for anyone with such infections to count on curing them by exercising to raise his or her body temperature."
Exercising During Illness
There is evidence that elevated body heat may be beneficial if a viral infection does not already exist, according to Dr. Peter G. Hanson, a cardiologist at the University of Wisconsin Medical School. "But I would be very cautious about any theory (suggesting) that people exercise during a viral illness. Strenuous exercise during acute viral illness may actually lead to viral damage to the heart," the physician warned.
Heber, Hanson and others are cautious about assessing the impact of exercise-induced body heat on infection because most studies on the subject have used small numbers of subjects and show the benefits only of acute exercise, not how long-term conditioning might increase the body's resistance to infection.
The exercise/immune theory is also criticized on the ground that fevers and exercise use different mechanisms to increase body temperature. Elevated temperature from fever results from activity in the hypothalamus, the "thermostat" in the brain that regulates body temperature. Exercise-elevated body temperature stems from building body heat faster than the body can get rid of it.
Kluger's studies of reptiles with bacterial infections show that when fevers are suppressed with drugs, the animals fare very poorly and most of them die; when they are allowed to generate fever, the animals usually recover.
Starving Out the Invaders
Fever is a protective device. When bacteria or viruses infect the bloodstream, a fever develops. Indirectly, that fever causes the invading organisms to starve.
Starvation of bacteria and viruses results from the release by white blood cells of the protein endogenous (within) pyrogen (fever producer), also called EP or interleukin-1. It is this protein that acts on the hypothalamus to cause the increased body heat associated with fever.
Cannon and Kluger reasoned that if EP is released during infection and produces a fever, then perhaps EP also is responsible for the elevated temperature that occurs after prolonged vigorous activity, which lasts for as long as 11 hours.
The two physiologists tested their theory on 10 men and four women who volunteered to pedal bicycles for one hour at 60% of their aerobic capacity. Blood taken from the cyclers before exercise and injected into rats had no effect on the animals, but blood taken after exercise did produce fever when injected into the rats.