It is possible to exercise yourself into illness. There’s a happy medium where sufficient quantities of exercise can bestow health benefits, including an optimally functioning immune system. But at the upper end of this spectrum, where extreme or exorbitant amounts of physical activity are undertaken, immune system suppression can be a consequence that leads to increased susceptibility to infection. Particularly, heavy training or competition loads undertaken by athletes can increase the risk of acquiring an upper respiratory tract infection (URTI), which can compromise the nasal cavity, mouth, and throat. URTI is an umbrella term that encompasses many infections that affect the upper respiratory tract. Infection types can include the following: tonsillitis, sinusitis, laryngitis, pharyngitis, the “common cold” (which can be caused by many different viruses), influenza, pertussis, and infectious mononucleosis.
One hypothesis as to why hard-training athletes may be more vulnerable to infection is that exhaustive exercise can create an ‘open window’ in the hours following a training session. In this post-exercise period, many components of the immune system may become depressed. While this effect is short-lived, if high-intensity training occurs frequently (as depicted in Figure 1) it can provide many repeated ‘windows’ for infection to opportunistic bacteria and viruses.
A potential contributing factor to this ‘open window’ is the availability of the amino acid tryptophan. During exercise, particularly of an exhaustive or intense nature, the body will accelerate its catabolism (i.e. breakdown) of tryptophan which may be utilized in energy (ATP) and serotonin production. A depression of tryptophan may be an indicator for a decrease in the body's immunosurveillance capability - the ability for your body to ‘check in’ on its immune functions. Prior data has indicated the gut microbiome can play a role in modulating tryptophan levels. In a study of endurance-trained men, supplementing with a probiotic containing six strains (Bifidobacterium bifidum W23, Bifidobacterium lactis W51, Enterococcus faecium W54, Lactobacillus acidophilus W22, Lactobacillus brevis W63, and Lactococcus lactis W58) attenuated markers of inflammation and intestinal permeability - factors that could bolster immune function. However, tryptophan metabolism was not assessed in that study, so its contribution to this effect could not be estimated.
In the study under review, the investigators sought to answer two questions:
Does the use of a multi-species probiotic preserve tryptophan levels?
Are higher tryptophan concentrations associated with a decrease in incidence of URTIs in actively training athletes?
Athletes undertaking intense or prolonged training loads may be more vulnerable to a category of illnesses known as upper respiratory tract infections (URTIs). This vulnerability may be due, in part, to the short-term suppression of some immune system components in the post-exercise window. Levels of serum tryptophan may be used as a marker to assess immune system function. The current study sought to determine if the use of a multi-species probiotic may be able to help fortify tryptophan levels during these intense training periods and stave off URTIs.