Exercise Appears to Boost Immune System - to a point
By: Judy Foreman
01/01/1996

You head out the door, virtue personified, for the first run, or at least brisk walk, of the year.

You know -- who doesn't by now? -- that regular exercise is great for your heart, your muscles, your mental health.

You may even think -- as exercisers usually do -- that working out is a tonic for your immune system. Indeed it may be, provided you don't push yourself to the max too often.

But as the once-tiny field of research into exercise and immunity blossoms -- the two-year old International Society of Exercise and Immunology wrapped up its second meeting in Europe recently -- researchers are finding that the links between exercise and immunity are more slippery than once thought.

The emerging picture, they say, is that any connection between exercise and, say, the risk of getting a cold, probably follows a J-curve, with both too little and too much exercise being deleterious, and moderate exercise, potentially beneficial.

But caveats are in order.

Compared to research on exercise and heart function, the study of exercise and immunity is in its infancy. Just figuring out what to measure is tricky
because exercise varies in type, intensity and duration, people vary in basic fitness and the immune system is one of nature's most complex creations.

Links between exercise and immunity are "interesting, but speculative," says Dr. Jerome Groopman, chief of hematology and oncology at Deaconess Hospital.

"What's required is a very critical look at how immune function is measured in these studies," he says.

Some studies do show that the activity of some immune cells "can be affected by exercise," says Roger Fielding, an exercise physiologist at Boston University. The problem is how to interpret this.

Blood counts of immune cells called neutrophils, for instance, "go up if you do a bout of exercise," Fielding says. But this may only be a sign that the inflammatory process by which the immune system repairs exercise-induced muscle tears is working, not a sign the body is better primed to fight infections or cancer.

With other measures, like observed increases in natural killer cells, it's unclear whether changes are big enough or last long enough to impact immunity, he says, adding, "I'm very skeptical."

Still, the consensus is that regular, moderate exercise "will boost some aspects of immune function," says William Evans, director of the Noll Physiological Research Center at Pennsylvania State University in University Park. "And it's likely that people who exercise regularly have lower rates of certain kinds of cancer and greater resistance to infection."

Studies from Texas, for instance, show that deaths from all causes -- including cancer -- are lower in people who are regular, moderate exercisers than in sedentary people.

"There's also evidence," says Evans, "that people who exercise regularly have higher levels of IL-1, a natural substance that raises body temperature -- producing fever -- and helps kill invading organisms.

David Nieman, professor of health and exercise science at Appalachian State University in Boone, N.C., has been finding growing evidence of links between exercise and immunity.

In two randomized, controlled studies, Nieman, president-elect of the exercise and immunology society, compared overweight, sedentary women who began a program of brisk walking for 45 minutes, five days a week, with matched controls who remained sedentary. He found the walkers suffered only half as many sick days for colds as the others.

More intriguing, Nieman found that the number of immune cells -- some of which normally live in the spleen and lymph nodes -- increased temporarily in the walkers' bloodstreams. There, at least in theory, they'd be more available to fight off germs.

Other researchers have shown that "graded exercise" may help people with HIV infection or chronic fatigue and immune dysfunction syndrome (CFIDS) -- perhaps by improving mood, which in turn may influence immune function. But this remains unproven.

Dr. Leonard Calabrese, head of clinical immunology at Ohio's Cleveland Clinic, has found that his chronic fatigue patients feel better if they walk a bit -- three to four minutes a day -- and increase this by one to two minutes every two weeks.

Graded exercise seems to benefit people with HIV infection, too, provided they are in decent shape to start with.

Among Calabrese's HIV patients, exercise seems to boost natural killer cells and at least does not decrease the number of CD4 cells, the main type of immune cell attacked by the AIDS virus.

Weight lifting, he finds, doesn't seem to affect the immune system, though it helps retain lean body mass.

And as with so much else in life, however, if you overdo it, exercise can become too much of a good thing. In fact, though many people exercise too little, some do far too much, especially world class athletes who, says Evans of Pennsylvania, "are always on the edge of overtraining."

"Excessive exercise can backfire," agrees Dr. Kenneth Cooper, founder of the Cooper Aerobics Center in Dallas. He believes too much exercise stimulates an outpouring of free radicals, chemicals formed in the body when oxygen is burned.

Whether free radicals -- which the body fights by increasing production of anti-oxidant enzymes -- impair immune function is not clear, but Cooper
recommends taking anti-oxidant supplements anyway, though others say the data to justify this is incomplete.

At the very least, there's growing evidence that athletes who push too hard for too long seem to be more susceptible to colds.

In 1987, Nieman surveyed 2,311 runners training for the Los Angeles marathon, including in his study both those who raced and those who dropped out for nonmedical reasons. He found that those who raced were six times more likely to get colds afterwards, a sign of how stressful the long race can be.

To see which immune components might be involved, he then coaxed 50 marathoners into his lab -- by offering $100 a head -- and asked them to run for 90 minutes to three hours on a treadmill at 80 percent of maximum aerobic capacity.

By measuring blood levels of immune cells -- neutrophils, monocytes, natural killer cells, T cells and B cells -- before and after the run, he found immune cells "leave the blood and go to muscles," presumably to repair damaged muscle fibers.

This suggests, he says, that the risk of infection may increase temporarily after a long, hard workout because "the front lines don't have as many soldiers," though immune function does bounce back to normal nine to 24 hours later.

Nieman also measured runners' levels of cortisol, a hormone and powerful immunosuppressant that soars in response to both mental and physical stress. He found that after a 3-hour morning run, cortisol soars and stays high all day.

For that reason, Nieman recommends that exercisers stay out of "cortisol country." The way to do that, his studies show, is to work out at 70 percent of your maximum heart rate for no more than 90 minutes per session.

The bottom line, says exercise physiologist Edmund Burke at the University of Colorado, is that while exercise is necessary, if done to excess "it's a double-edged sword."

And while most of us need to hear primarily the first half of that message, some need to hear the last.

Indeed, Bicycling magazine, citing two small but alarming studies in Poland and Australia, recently warned that while riding hundreds of miles a week leads to fitness, it may also lead to impaired immunity.

Nieman came to that same conclusion two years ago. After running 58 marathons, he quit. "My own research was convincing me it was not a healthy thing to do," he said.

To increase fitness without damaging muscles or the immune system, exercise physiologists suggest several DOs and DON'Ts:

SIDEBAR:
EXERCISE: THE RIGHT WAY AND WRONG WAY TO DO IT

DOs

• Spend at least 30 minutes on moderate physical activity on most, preferably all, days -- brisk walking, cycling, swimming, yard work, etc. -- either continuously or in 10-minute bouts.
• If you run, a good goal is 10 to 15 miles a week. More than that won't boost longevity or health, and running more than 30 miles a week may be detrimental.
• To maintain muscle mass and bone density, lift weights two to three times a week. Weights should be heavy enough that you can only lift them 8 to 10 times before needing a rest.
• For cardiovascular conditioning, keep your heart rate at 65 to 90 percent of maximum for 30 minutes, three to five times a week. To find the right range for your heart rate, subtract your age from the number 220, then multiply the result by 0.65 to get the minimum, by 0.9 for the maximum.
• If you have a serious disease such as HIV infection, chronic fatigue syndrome or cancer, ask your doctor about exercising. Moderate exercise, under supervision, may be beneficial.
• Eat a balanced diet, with lots of fruits and vegetables, and allow time for sleep and rest.
• The data is incomplete, but some specialists recommend anti-oxidant supplements if you exercise heavily: 1,000 milligrams a day of vitamin C, 400 International Units of vitamin E and 25,000 International Units of beta- carotene.
• Follow the NECK UP rule for exercising with a cold -- if symptoms are primarily nasal, exercise as usual.

DON'Ts

• Don't exercise if you have symptoms below the neck such as a bad cough or a fever or muscle aches. Muscle aches may be a sign of infection with the coxsackie virus; exercise can cause this virus to migrate to the heart, with potentially fatal consequences. If you're coughing from bronchitis, exercise may trigger asthma.
• Don't exercise hard for any more than 90 minutes at a time to avoid release of cortisol, a stress hormone and immune suppressant.
• Don't over train lest you compromise immunity, especially if you have other stresses like major job problems or divorce.
• Don't expose yourself to unnecessary germs if you're training hard. Avoid crowds when you can, wash hands and disinfect things other people touch, like telephones, door knobs or keyboards.
• Don't lose weight too fast. Losing more than two pounds a week may compromise T cells. If you exercise and starve yourself, your body may interpret this as stress and pump out cortisol.

Judy Foreman’s column runs every other week. Past columns are available on www.myhealthsense.com.

 Listen to her live call-in webcast radio show every Wednesday night from 8:30 to 9:30 EST on http://www.healthtalk.com.