Prolonged, intense physical exercise is challenging for our immune system. In fact, evidence suggests that for a brief amount of time immediately after a workout, our body is more prone to disease. New research examines the best strategies for recovering after intense exercise.
In the long run, physical exercise is extremely beneficial for our health. Scientific evidence strongly suggests that moderate to intense physical activity reduces the risk of heart disease, stroke, diabetes, and various forms of cancer, and it improves longevity overall.
However, immediately following a workout - particularly in the case of athletic, endurance exercise - the body's immune system is strained. Heavy exercise causes intense physiological stress, which has been linked to a high risk of infections and overall immunodepression.
Since nutrition affects almost all aspects of the body's immune system, research into the effects of nutrients on the body's ability to recover is highly significant.
One such study has recently been published in the Journal of Applied Physiology.
The research was led by Dr. Jonathan Peake and Dr. Oliver Neubauer, from the Institute of Health and Biomedical Innovation at Queensland University of Technology in Australia, and comprises a review of existing studies on exercise and immunity.
The effect of intense exercise on the body's immune system
The analysis confirms the notion that intense exercise causes a brief period of immunodepression during post-exercise recovery, and that repeated episodes of intense physical activity may raise the risk of illness.
However, the research also points out that, with the exception of salivary Immunoglobulin A, the exact biological markers signaling this immunodepression have not yet been identified.
The research also confirms that exercise can increase and decrease immune blood cell count. Specifically, it increases levels of circulating neutrophil and monocytes, but reduces circulating lymphocytes during recovery.
However, as the lead author explains, the studies reviewed did not support the common belief that regular exercise - without sufficient breaks in between to allow the body to return to normal - weakens the immune system.
"People often have fewer natural killer white blood cells after a workout, but we now believe they move to other parts of the body, rather than being destroyed," explains Dr. Peake. "Exercise is a form of stress, and more vigorous exercise creates more physiological stress which causes physiological and biochemical changes in the body," he adds. "To tackle the potential threats these changes highlight, the immune cells may simply move out of the bloodstream to the lungs [or the gut], for example."
These changes in immune function that suggest the relocation of immune cells have been noticed by assessing isolated cells ex vivo and in the blood. There is some evidence that the same results have been obtained in vitro, but the authors caution that more evidence is needed to verify this.
Carbs alleviate exercise-induced immunodepression
Dr. Peake warns that despite the body's attempts to protect itself immediately after exercise, intense physical activity still leaves the body more prone to infections:
"This still leaves our bodies vulnerable to infections and, generally speaking, the more strenuous the exercise, the longer it takes for the immune system to return to normal. Epidemiological evidence suggests that regular moderate exercise protects against upper respiratory illnesses, like the common cold, whereas regular intense exercise increases the risk of upper respiratory illnesses."
The most effective nutritional way to avoid these negative changes in the immune system appears to be the consumption of carbohydrates. The research review shows that consuming carbs during or immediately after exercise reduces exercise-related immunodepression and helps the body to recover.
Co-lead author Dr. Neubauer explains that this is particularly helpful for people who undertake high-intensity activity for sessions of 90 minutes or more:
"Between 30 and 60 grams of carbohydrates every hour during exercise help to support normal immune function. Examples of carbohydrates that could be consumed during exercise include carbohydrate-containing fluids, gels, and bars consisting of different carbohydrates such as glucose and fructose. Alternatively, bananas may also do the job," Neubauer adds.
Dr. Peake explains that the reason why carbs are so beneficial could be that they maintain blood sugar levels. "Having stable blood sugar levels reduces the body's stress response, which in turn, moderates any undesirable mobilization of immune cells. However, more research is warranted to verify that this also helps to prevent infections and illnesses," Dr. Peake cautions.
Overall, however, carbs seem to have a proven benefit, particularly for athletes.
"Consuming carbohydrates in the first few hours immediately after strenuous exercise also helps to restore immune function. This is especially important in situations where the recovery duration between two consecutive exercise sessions is short, which is often the case for athletes."
Dr. Oliver Neubauer