 Moderate exercise improves immunity and decreases illness rates. By far the most important finding that has emerged from exercise immunology studies over the past two decades is that positive immune changes take place during each bout of moderate physical activity. Over time, this translates to fewer days of sickness, with the common cold and other upper respiratory infections. We're talking a 25 to 50% reduction in sick days. I named one drug or supplement that can do that, and it doesn't take much. Let kids run around for just six minutes, and you can boost the numbers of immune cells circulating their bloodstream by more than a third. And at the other end of the life cycle, exercise may help prevent age-related immune decline. Sedentary women in their 70s may have a 50% chance of getting an upper respiratory illness during the fall season every year, but walk a half hour a day, and your risk is down to 20%. And the runners in the group got it under 10. That's just like a five-time better immune system. Now, while regular physical activity improves immune function and lowers upper respiratory infection risk, sustained and intense exertion may have the opposite effect, forming a so-called J-shaped curve relationship. As you go from inactive to active, your infection risk declines, but hardcore athletes that over-train may actually put excessive stress on their bodies and increase their risk of infection. Then you could lose training days, your performance could suffer. So what can you do? Well, traditional sports medicine doesn't appear to have much to offer, advising athletes to, you know, don't pick your nose, avoid sick people, get a flu shot. A new study, though, found that one can better maintain one's level of circulating white blood cells after exhaustive exercise by consuming a special type of fiber found in bakers, brewers, and nutritional yeast. Brewer's yeast is bitter, but nutritional yeast has a nice cheesy flavor. I use it mostly sprinkle on popcorn. Anyway, normally two hours after cycling your brains out, you can experience a dip in circulating monocytes, one of our first line of defense white blood cells. But those who had been eating the equivalent of less than three quarters of a teaspoon a day of nutritional yeast ended up even better than when they started after strenuous exercise. But does this increase in immune cells translate into fewer illnesses? Well, let's try it on some marathon runners. In the weeks following the Calls Bad Marathon, this is how many runners reported to experience upper respiratory tract infection symptoms taking a placebo. But if instead they had the equivalent of a daily spoonful of nutritional yeast, they cut their rates in half. What's even more remarkable is that they felt better. They asked how they felt on a scale of 1 to 10. People taking the sugar pills were like, OK, down around 4 or 5, but those taking identical looking capsules of the fiber found in nutritional yeast were up at like 6 or 7. Evidently, elite athletes tend to normally experience deterioration and mood state during intense training periods and before and after a marathon race. But sprinkle a little spoonful of nutritional yeast, and you may feel less tense, less fatigued, less confused, even less angry, and my favorite, significantly more vigor.