Endurance athletes who swill a carbohydrate drink are not only helping their muscles but also their immune systems.
Running a marathon, competing in a long-distance cycle race or doing an extended workout can stress out your immune system enough to make you ill. In fact, research suggests that marathoners are six times more likely to become ill following their 26-mile races than the average person in the street or the runner who puts in an easy three-miler.
Likewise, heavy-duty training carried out over a period of several weeks can also strain your immune system. This strong link between illness and strenuous training explains why recurrent infections, especially in the upper-respiratory system, represent one of the key indicators of overtraining in athletes. When sports-active people try to do too much, their performances slide and they fall ill.
Learning how to avoid overtraining is one way to stay well, but that's much easier said than done. One key problem is that the physical strain of training is just one of the stressors which can make your immune system slide: vocational, emotional, and other difficulties also take their toll. A particular 'dose' of training might be okay for you at one time of the year but make you ill at other times - when you're under a lot of psychological stress.
Staying away from marathon-type efforts is another doctor- avoidance technique, but that's a strategy which is quite unpopular with marathon runners and long-distance cyclists who really enjoy their pursuits.
So, what's another, relatively easy way to prevent training-related illnesses? Would you believe that taking in a little more sugar would do the trick? Sugar? That white stuff that's maligned by health-food buffs? Well, yes: sugar - ingested before, during, and after your strenuous exertions - can exert a 'ripple' effect that helps keep key hormone levels under control and relieves stress on your immune system.
The research
We know this thanks to pioneering work carried out by Dr. David Nieman and his colleagues at Appalachian State University in Boone, North Carolina and Loma Linda University in California. Recently, Nieman and co-workers divided 18 experienced marathon runners into three groups. Runners from one group ingested 1000 mg of vitamin C daily for one week. On the eighth day of the study, these runners drank about 24 ounces of the sports drink Gatorade and then - 15 minutes later - went for a two-and-a-half hour run at an intensity of about 75 to 80 per cent of VO2max (85-88 per cent of max heart rate). During this run, the subjects swigged about eight ounces of Gatorade every 15 minutes (one litre per hour), providing a total carbohydrate intake of around 60 grams per hour. Following the run, the athletes drank about 16 ounces of Gatorade per hour for 1.5 hours and then 8 ounces per hour for the next 4.5 hours.
Members of the second group ran and consumed Gatorade in an identical fashion but took no supplemental vitamin C during the week preceding the big run. Runners in the third group also took part in the 2.5-hour run, but they ingested no vitamin C during the pre-run week and swallowed only a carbohydrate-free, placebo drink during the long exertion. All runners followed a high- carbohydrate diet (60 per cent of calories) during the week before the marathon-type effort.
The results?
Although it's a popular nutritional practice among health- conscious athletes, vitamin C supplementation had no effect at all on immune-system functioning following the 2.5-hour run. Instead, the big story was carbohydrate: runners who took in the carbohydrate- containing Gatorade had low neutrophil-to-lymphocyte ratios after their exertions, while placebo runners had high ratios of neutrophils to lymphocytes.
You see, neutrophils and lymphocytes are both blood white cells which can help to fight infectious organisms, but their relative numbers tell you a lot about how your immune system is functioning. If you have lots of neutrophils cruising through your blood and few lymphocytes, your immune system is under duress and you're probably more prone to illness. Step down the neutrophils a bit and boost the lymphocytes and your immune system is strong and ready to take on the whole world (of pathogens).
Now, remember that the Gatorade runners had low neutrophil to lymphocyte ratios, indicating that their immune systems were in great shape, even after their taxing, 2.5-hour exercise. The placebo runners were in trouble, checking in with lots of neutrophils and scanty quantities of lymphocytes. Bottom line? Taking in Gatorade before, during, and after your prolonged exercise is good for your immune system (well, let's be fair; most sports drinks on the market resemble Gatorade pretty closely, so we should really say that using a carbohydrate-containing sports beverage is good for your immune functioning).
Cortisol is the culprit
Surprisingly enough, much of our knowledge about white cells and immune system duress comes from research carried out with race horses. Of course, there's been keen scientific and medical interest in keeping high-stakes race horses healthy and happy, and one of the key discoveries in equine research has been the link between neutrophil/lymphocyte quantities and overall health.
The overall set-up is surprisingly simple. 'Basically, you have a health triangle which must remain intact if you want to stay well,' says Nieman. 'The three corners of the triangle are (1) blood glucose, (2) hormone levels, and (3) the movements of various kinds of white blood cells in and out of the bloodstream.'
The interactions between the three sides of the triangle occur in the following way. If you go for a long run (probably longer than an hour or so) without taking in adequate quantities of carbohydrate, your blood-glucose levels begin to drop. Your brain deplores this situation, because it greedily wants to consume blood sugar at high rates. To keep the carbos coming, the brain initiates some physiological processes which raise blood levels of two key hormones - cortisol and epinephrine. This pair of endocrine products do give the sugar-junkie brain a bit of a high, but they also have a pronounced effect on the third side of the triangle - white blood cells. The bigger hormonal player is cortisol, which 'kicks' lymphocytes out of the blood and 'pulls' neutrophils in. The result is a stressed- out immune system which doesn't do a great job of warding off infection.
Now, note that the whole sickness-producing chain of events could be stopped in its tracks if blood-glucose levels stayed high.With lofty blood sugar, the brain wouldn't call for cortisol. Cortisol wouldn't augment the blood's neutrophil ranks and thin the numbers of lymphocytes. Your immune system would stay okay. And there, in one easy lesson, you have an understanding of the incredibly positive effects of a little sugar on the immune system during exercise. If blood glucose stays high, there is little immune suppression associated with exercise, even during long bouts of exertion.
Rebuilding muscles
Keeping blood glucose in line can help prevent other kinds of problems, too. For example, when you go out for a long run, lots of potentially bad things happen to your muscle cells. Muscle membranes become frayed, cells begin to break down and spill out their contents, and energy levels become depleted. It's a mess! You need to recover from such mayhem as quickly as possible, but there's one huge, potential problem: cortisol, the hormonal culprit we mentioned above, tends to enhance protein catabolism, e.g., the further breakdown of key components of muscle cells.
Of course, that's to be avoided at all costs. And a key way to reduce cortisol and get muscles to rebuild rather than further destroy themselves is to ensure that blood-glucose levels stay high. As long as blood sugar stays up, you can attenuate any negative rises in cortisol.
As we mentioned, Gatorade is good for doing that. So are the other sports drinks. If you're going to be exercising for more than an hour, you should ingest approximately 12 ounces about 10 to 15 minutes before you start (the Appalachian State marathoners used 24 ounces, but that can be pretty heavy in the gullet). Then, take in five to eight ounces every 15 minutes as you exercise. Follow your workout with a decent carbo intake, too (sports drinks are nice, but you can also use real, easily digested, carbohydrate-rich food). If you do, you'll help keep your immune system - and your muscles - in tip-top shape. And you'll also recover more quickly and train more consistently. And that, my friend, is one of the key secrets to success as an athlete.
Jim Bledsoe