The notion of an Ironman triathlete laid up in bed with a cold may seem like a contradiction, but in reality, endurance training and triathlon competitions can temporarily impair immune function, leaving you vulnerable to colds.
Researchers found that among 150 ultra-marathon runners competing in a race in South Africa, one-third developed upper respiratory tract infections within two weeks after the race. Among more than 1,800 runners competing in the Los Angeles Marathon, almost 13% reported coming down with a cold within a week after the race. And in the Western States Endurance Run, about one in four athletes reported symptoms of an upper respiratory tract infection within two weeks after the race.
Why the spike in colds after these endurance events? The thinking is that the physical stress of endurance exercise increases the circulating concentrations of stress hormones like adrenaline and cortisol. In the short term, these hormones can help you meet the immediate physical demands of Ironman competitions, but the price paid can be a temporary suppression of the immune system — often just enough to allow a head or chest cold to set in.
So, how do you reap the benefits of your training, and compete in an Ironman triathlon, without suppressing your immune system? Nutrition may help.
A possible key strategy for avoiding the immunosuppressive effects of heavy exercise is to ensure that your diet provides all that you need in the way of nutrients and other dietary factors that play important roles in supporting immune function. For example, protein in the diet is important because many components of the immune system are made up of protein. In addition, essential vitamins and minerals are needed to support the rapid replication of immune cells that are critical to warding off cold bugs and other infectious agents.
Calories are important, too. As an Ironman triathlete, you train long, hard hours, and it can sometimes be a challenge to meet your daily calorie needs. Or, perhaps you’re ramping up your workouts while cutting calories, to try to get leaner. Unfortunately, that seems to be a quick route to a cold. Scientists have found that, in endurance athletes, even a few weeks of dieting to lose weight can impair the function of your immune cells. To ensure that your immune system stays strong, avoid dieting or inadvertent calorie shortfalls during periods of heavy training and strenuous competition.
Your intake of carbs also seems to play an important role in immune function. Studies show that athletes eating low-carbohydrate diets who engage in prolonged strenuous exercise show sharp increases in circulating levels of stress hormones. As stress hormone levels rise, the number and activity level of key cells involved in immune function decline. However, consuming carbs during exercise reduces the rise in stress hormones and helps to offset the suppressive effect on immune function. Will this translate to fewer colds? No one knows for sure, but given that carbs during exercise have been shown to extend endurance, the potential immune system boost is a bonus.
There is no strong evidence that any specific nutrient or herb can offset the effects of strenuous exercise on immune function, and few studies have actually looked at the effect of these dietary factors on rates of upper respiratory tract infections. However, the exception seems to be vitamin C. In two different studies, ultra-marathon runners taking 500 to 600 mg of vitamin C daily for a few weeks before and a few days after an ultra-marathon had lower rates of upper respiratory tract infections compared to those taking a placebo. Unfortunately, other investigators weren’t able to replicate these findings, so definitive proof is lacking. Nonetheless, taking a daily, 500-mg vitamin C supplement or boosting your vitamin C intake from fruits and fruit juices for a few weeks before and the week after competing in a triathlon might be a measure to consider. Plus, a reasonable argument can be made for taking a balanced, once-a-day-type multivitamin/mineral supplement to help ensure that you are consistently getting adequate amounts of the micronutrients needed to support your immune system.
There is some emerging evidence of other dietary factors (e.g., probiotics, glutamine, and whey protein) having roles in supporting healthy immune function, but more research is needed to see if these types of dietary factors help with the temporary suppression of immune function that occurs in endurance athletes in particular.
In summary, here are some things you can do to help avoid the Ironman sniffles:
- Make sure not to compound the physical demands of the event itself or difficult Ironman training days by scrimping on calories.
- Consume carbs during the event — they not only can increase endurance but also may reduce the immune-system suppression associated with strenuous endurance exercise.
- Consider a daily multivitamin/mineral supplement to ensure that your diet always has an adequate supply of the nutrients needed to support immune function.
- A little extra vitamin C a week or two before and after the event may give your immune system an added boost.
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Reference:
Gleeson M. Can nutrition limit exercise-induced immunodepression? Nutr Rev. 2006;64:119–131.
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