In recent times, the attention of scientists has been focusing on the so-called gut-lung axis and on the connection between the health of the intestinal microbiota, that is, the intestinal flora, and that of the respiratory tract, especially in case of viral infections. In particular, it seems increasingly clear that the intake of probiotics through the diet can have a protective role on the upper and lower airways by modulating the immune response and inhibiting the replication of the virus. This is also the result of a very recent review published a few weeks ago in the journal Nutrients by a team of Finnish researchers (Lehtoranta et al, Nutrients, Sep 2020).
Respiratory viruses cause an infection in the body that can affect the upper respiratory tract, such as a cold, or the lower respiratory tract, such as bronchitis or pneumonia. The oral intake of probiotics has as its primary goal to benefit the intestine, however, it also seems to have an impact on the health of the respiratory tract. First of all, following oral intake of probiotics it was possible to detect these substances even in tissues that did not belong to the gastrointestinal tract, such as tonsils, adenoids and the nasopharyngeal mucosa. Then, probiotics, since they act by modifying the intestinal microbiota, supporting and strengthening it, and since the health of the entire organism also depends on the health of the microbiota, are able to indirectly improve the immune response. Not only that, scientific studies have observed that probiotics can stimulate the response of the innate immune system, which is the first line of defense against virus attack. In addition, it has been shown that the intake of probiotics is linked to a lower viral presence in the lungs following the infection caused by the flu and also to a lower level of inflammation in the lungs through the inhibition of proliferation of the virus. It is important to remember, in fact, that an excessive immune response through the mechanism of inflammation can cause greater damage than the viral infection itself.
What emerges is, as pointed out by the authors, that the intake of probiotics is linked to a lower incidence and duration of respiratory tract infections, both in adults and children. However, other studies will have to follow to understand the exact mechanism that makes probiotics so beneficial not only for the intestine but also for the health of the airways.
Finally, probiotics are contained in sauerkraut, miso, soy sauce, tempeh, olives, pickles and yogurt. However, for what concerns yogurt, this should be indicated on the label because not all yogurts contain probiotics, as we have seen thanks to a previous article entitled Probiotics and yogurt.