With colds and flu, as in war, defense is the best offense.

With colds and flu, as in war, Defense Is the Best Offense

It's that season again. Have you felt the symptoms yet? Runny, stuffy nose; scratchy, sore throat; with some coughing? Then you probably had the cold, an affliction that children experience an average of six to 10 times a year and adults two to four. If the onset was more sudden, the symptoms more severe, including headache, high fever, and extreme fatigue and weakness, then, most likely, you had the flu (see box 1).

These uppower respiratory tract infections, as physicians and researchers call them, cost us more than physical suffering. The Centers for Disease Control has estimated that the 429 million colds and flu that occur annually in the United States result in $2.5 billion in lost school and work days in addition to medical costs.

Science has yet to discover a cure for the common cold and flue. While the proper use of nonprescription drugs such as decongestants, antihistamines, and cough suppressants can be effective in relieving many of the symptoms, they do not cure these conditions.

Preventing colds and flu, most scientists agree, is ideally accomplished by avoiding exposure to the viruses that cause them. The viruses are spread by microscopic droplets of body fluid from secretions we breathe out all the time. Our hands, eyes, lungs, and skin are in contact with them constantly. Many researchers believe that as we rub our eyes and touch our mouths and noses, we bring the virus into contact with mucous membranes that transmit the virus into our bodies. As we breathe the air near sick people, the viruses can also be transported in. Completely avoiding cold and flue viruses thus appears nearly hopeless, unless one lives as a hermit on some distant Pacific island.

So having a strong immune system within our bodies becomes all-important. If the war cannot be prevented, a strong defense system may win the day. As the viruses enter the body they encounter a legion of nearly 1 trillion highly specialized cells that have the marvelous ability to identify and destroy all foreign substances (see box 2). Keeping this army vigilant and healthy is where you and I get involved.

The immune system can be weakened or strengthened by several lifestyle factors. Most vitamins and minerals are important for proper immune function. Many researchers have shown that undernutrition such as is common in developing countries impairs the immune system. On the other hand, obesity and excessive intake of polyunsaturated fatty acids (plant oils), iron zinc, and vitamin E also suppress immune function. And nearly all scientific studies have failed to show that large does of vitamin C prevent colds and flu. Thus a balanced diet without vitamin and mineral supplements appear most helpful.

Mental stress also depressed the activity of the immune system. Marital discord, excessive life change and undue depression and anxiety have each been shown to enfeeble immune function. Widowed women, for example, have considerably more episodes of colds and flu than married women. In a six-month study conducted in Australia, people measured as having high stress in their lives experienced twice as many days with cold and flu symptoms as a low-stress group. Moderating life change and stress, and taking time to sleep and relax, are important weapons in shoring up your defense system.

The role of exercise. Many exercise buffs believe that regular exercise promotes "resistance" to colds and flu. In one study that I conducted on a group of runners training 40 miles a week, 90 percent felt that their exercise program during the previous five years had helped them to reduce their risk of colds and flu. Interestingly, however, 70 percent felt that following intense marathon race events, their risk was increased.

The physician of the U.S. cross-country ski team has also noted that toward the end of the competitive season, there is a high incidence of respiratory illnesses, resulting in a significant loss of skiers from active competition. European investigator have reported an increased incidence of infections in highly trained sportsmen at the time of intensive training. At the recent Olympic Games, some of the worked's premiere athletes, including Sebastian Coe, were unable to complete because of illness through overtraining. Earlier in this century, some clinicians observed that severe exertion was associated with an increase in incidence and severity of the paralytic form of polio. Many animals studies have also shown that excessive exercise decreases resistance to infection.

These observations have led to a flurry of research during the past several years by investigators around the world. My research team at Loma Linda University has been one of the most active.

One of our first studies involved 2,300 marathon runners who participated in the March 1987 Los Angeles marathon. We looked at the incidence of colds and flu during the two-month period prior to the race (peak cold and flu season) and the week following the race event. Slightly more than 40 percent of the runners reported at least one cold or flu during the two months before the race, and runners training more than 60 versus less than 20 miles a week doubled their odds of getting sick. Most important, 13 percent of runners who ran the race became sick during the week after, in comparison to only 2 percent who trained for the event but then decided not to run. Controlling for important factors, we concluded that the odds of getting sick after running a marathon race are six times greater than for equally experienced runners who do not. These research findings suggested to us that the combined physical and psychological stress of running a 26.2-mile marathon depressed the immune system in some way.

We next brought 10 seasoned marathoners to our Human Performance Laboratory, and ran them at their fastest pace for three hours while collecting blood samples before, during, and one day following the run. The blood was analyzed carefully for many immune system parameter and hormone changes.

Our most important finding was that the stress hormone cortisol increased 50 percent above pretest levels after the run, which depressed natural killer cell activity more than 30 percent for nearly six hours. Natural killer cells play an important role in the body's "first-line defense" against foreign invaders. More research needs to be conducted to confirm our findings, but we propose that subsequent to an exhausting marathon run, for at least six hours the immune system is more vulnerable than normal to attack by foreign invaders.

Our next step was to research whether or not moderate exercise was beneficial in reducing the risk of coming down with a cold or flu and in strengthening the immune system. We selected 50 women who were not on an exercise program, and randomly divided them into exercise and nonexercise groups. For 15 weeks (February through mid-May), the exercise group briskly walked 45 minutes, five days a week, at 60 percent of their maximum oxygen capacity. Subjects in both groups recorded how they felt, using daily logs with a special health coding system. This was the first study ever to investigate the relationship between moderate exercise training, immune system function, and upper respiratory tract infections.

To our pleasant surprise, the women in the walking group experienced half the days with cold and flu symptoms during the 15-week period as compared with the nonexercise group (5.1 versus 10.8 days). Natural killer cell activity increased in the walking group from the very beginning of the study, a finding opposite to that of the marathon runner study. Other components of the immune system changed in such a way that it was prepared to deal more successfully with an infectious challenge. These results suggest that moderate exercise is beneficial in strengthening the immune system and lessening the onslaught of winter sickness.

Practical advice. Our research findings and those from other laboratories in South Africa, Russia, and Europe indicate that the combination of intense training and the stress of competition makes some athletes more susceptible to infection because of suppressed immune systems. On the other hand, moderate exercise appears to be protective, enhancing immune function. The "J-shape" relationship between exercise and risk of colds and flu is depicted in Figure 1.

Although brisk walking was the mode of exercise used in our study, there is every reason to believe that moderate jogging, swimming, cycling, and other aerobic exercise are just as beneficial. The important principle is that of moderation. When exercise becomes stressful (high intensity or long and exhausting), cortisol rises strongly in the bloodstream. This hormone has been shown to depress the ability of certain immune cells to function properly.

For those athletes who must exercise intensely for competitive reasons, several precautions can help decrease the risk of sickness. Sensible practices include spacing vigorous workouts and race events as far apart as possible, eating a well-balanced diet, keeping other life stresses minimal, avoiding over-training and chronic fatigue, and obtaining adequate sleep. There are many other risks involved in training for competitive athletic events, including muscle, bone, and joint injury, menstrual cycle disturbance, iron deficiency, and heat injury. All of these risks can be minimized by prudent training practices. Nonetheless, the decision to train intensely for competition should be made circumspectly. Athletes pay a painful price for their achievements.

A final word of advice based on personal experience. Following intense race events, be unusually careful (for at least six hours) to avoid people who are sick. I learned this the hard way a few years ago. I had just run a hard 13.1-mile race; then I rode 45 minutes home in my pickup truck with a friend who had a cold and a stomach virus. Because the day was cool, I kept the windows up. The next evening, I came down with the exact same symptoms that my friend was experiencing.

David C. Nieman, D.H. Sc., M.P.H., F.A.C.S.M., is chairman of the Department of Health Science at Loma Linda University's School of Public Health.