Introducing our Research Spotlight!

Our new feature series highlights research that is of interest to those fascinated by the science of the gut microbiome, helping to connect the dots between research study and real-world application.

Exercise-Induced Bronchoconstriction (EIB) and the gut microbiome

This Research Spotlight introduces Exercise-Induced Bronchoconstriction, a physical response to exercise that is of concern to both athletes and recreational exercisers.

Read further to see how gut microbiome modulation could be adopted by athletes and exercisers.

What is EIB?

Exercise-Induced Bronchoconstriction (EIB) was first recognised in people with asthma in response to exercise in the 1960s, where forced expiratory volume (FEV1) was reduced with exercise duration of 5-10 minutes and fell below the resting level during and after the exercise.

The FEV1 reduction was a result of bronchoconstriction1. Later, it was found that environmental factors such as humidity and air temperature can affect EIB. demonstrating the significance that environment has for both the athletic population and general public2.

EIB is described as acute airway narrowing as a result of exercise (during or after), occurring in a large proportion of patients with asthma, as well as in patients not known to have asthma. The high prevalence of EIB in athlete populations is partly a response to the environmental conditions including pollution and air conditions.

EIB occurs as a result of drying of the airways, causing the release of inflammatory mediators. The condition can be treated pharmacologically using short-acting beta2 agonists or long-acting beta2 agonists. Non-pharmacological methods are often used to minimise occurrence, these include warm-ups using a scarf or face mask to humidify the air, losing weight if necessary, improving overall fitness levels or modifying dietary intake3.

Population effects of EIB

The prevalence of EIB is between 5-20%, however the true prevalence is not known due to a lack of epidemiological studies differentiating between asthmatics and non-asthmatics. There is a high prevalence of Exercise-induced Bronchoconstriction in the asthmatic population because asthma is a comorbid factor for EIB, and 90% of asthmatics will experience EIB.

There is a greater prevalence of EIB in performance athletes compared to the general population due to inhalation of dry, cold air and air pollutants. There is also a higher prevalence of EIB in children, particularly children in urban environments compared to the general population4.

There is an effect on quality of life (QOL) in those who experience EIB due to the physical and emotional burden. Almost half the patients with asthma report that their participation and performance in sport is affected4. This has public health implications, as well as affecting the wider health of these patients. In turn, this demonstrates the need for effective management of EIB.

Managing EIB in patients with asthma

There are global guidelines to follow when seeing patients with asthma and this could be referred to for medications and other management options5.

Exercisers and athletes are additionally recommended to add a 10 to 15-minute moderate intensity warm-up as a ‘refractory period’ before the planned activity, to allow their body to adjust. Performance nutritionists need to be aware of the World Anti-doping Agency’s guidelines6, inform the athlete and encourage them to discuss the best option for them with their GP.

EIB and prebiotics

In the literature, Hyperpnoea-Induced Bronchoconstriction (HIB) is commonly referred to in place of EIB, due to it being a highly reproducible surrogate for EIB. Under laboratory conditions, HIB tends to be a simulation of EIB7.

Systemic inflammation can be part of asthma, whether that be a cause, an effect, or both is uncertain. Diet can reduce systemic inflammation, just as a Western Diet has been demonstrated to promote a pro-inflammatory environment, due to a lack of antioxidants and a surplus of saturated fatty acids, associated with immune activation8.

Additionally, the gut microbiome can be responsible for metabolites that affect immune and metabolic responses.

Short chain fatty acids (SCFAs) are metabolites associated with immunomodulation and produced when prebiotic fibre found in fruit, vegetables, grains, legumes and pulses are fermented8. Whilst the dietary effect on asthma is inconclusive, a Western Dietary pattern appears to have a detrimental effect on asthma8.

Prebiotic supplements can be used when a person may find it difficult to include enough fibre in their diet. A prebiotic galactooligosaccharides (GOS) mixture, including Bimuno®, reduces severity of HIB, the surrogate for EIB, and markers of airway inflammation9.

This study highlighted in this Research Spotlight included 18 participants, of which 10 people with asthma were in the HIB group and 8 were in a control group, with no history of asthma.

Each group had five male participants and both groups were randomised for a crossover design to supplement with either Bimuno or placebo, with a 14-day washout period. The eucapnic voluntary hyperpnoea (EVH) method was used to cause a highly reproducible HIB in a laboratory setting9.

Bimuno supplementation reduced the severity of HIB, determined with reduced systemic Th2-driven inflammatory markers. Through its impact on the gut microbiome, this research suggests that Bimuno has the potential to modulate the underlying immunopathology of asthma, and thereby reduce hyper-responsiveness of the airways that is associated with HIB/EIB.

The precise mechanisms by which Bimuno modulates immune function and reduces airway inflammation is unclear and requires further exploration9.

Exercise and the immune system

The findings above suggest that prebiotic GOS supplementation can modulate the immunopathology of asthma, and since asthma can be exacerbated by exercise, there are other interactions to consider between exercise and immunity.

There is a J-shaped curve demonstrating the association between exercise training load and infection risk. At the highest training loads that performance athletes undertake, their infection risk is higher than those exercising at lower levels, particularly risk of upper respiratory tract infections (URTIs)10.

Similarly to how prebiotics reduce inflammation associated with EIB in the above example, nutrition appears to have immunological benefits in high exercise loads. Carbohydrate, protein and fluid intake are important in post-exercise recovery to prevent exercise-induced immune impairment.

While macronutrients play a role in recovery and immune modulation, micronutrients and non-nutritive food compounds including antioxidants can improve the inflammatory response to physiological stress in high exercise loads10.

Probiotics and prebiotics, as nutritional supplements used in athlete and non-athlete populations, have demonstrated reduced inflammation and less occurrence of URTIs during times of high exercise load10.

It seems apparent that a dietary pattern could be the ultimate recommendation for athletes to maintain optimal functioning of their immune system, whether that be related to URTIs or EIB. More research on diet and asthma, and using nutrition for health and performance in athletes, is more important than ever.


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