Gut health and allergies - how they are associated with each other

More and more studies suggest that there is a link between the excessive immune response that occurs with allergies and an imbalance in the intestine. This is not all that surprising, as the gut and immune system are closely linked. Containing almost 80 percent of all immune cells, the intestines are home to the vast majority of our immune system. Together with an intact intestinal mucosa, which represents the mechanical boundary, the intestinal flora and the intestinal immune system form a 3-phase defence against undesirable germs and substances. If the intestinal balance is impaired (e.g. due to a miscolonisation in the intestinal flora and/or a damaged intestinal mucosa), this can also affect our immune system and promote the onset of hypersensitivity or an overreaction to allergens.

The intestinal flora interact with our immune system. Useful intestinal bacteria not only fight off pathogens and pollutants, but also act as a "training camp" for our entire immune system. Here, our immune cells collect valuable "fighting" experience and also learn – especially in the first year of life – to distinguish between friend (the body's own or harmless antigens) and enemy. This “immune tolerance” is considered an important property of an intact immune system. In addition, these microscopic intestinal inhabitants also stimulate the formation of the body’s own defences, which benefit the entire organism.

However, our own bacterial zoo does not just train our immune cells. It also strengthens our intestinal barrier by breaking down non-digestible fibres into short-chain fatty acids, which in turn nourish our upper intestinal mucosal cells. If, however, the barrier function of the intestinal mucosa is impaired, uncontrolled substances such as allergens can increasingly enter the bloodstream and thus promote hypersensitivity or an overreaction of the immune system.

Allergies are becoming increasingly common worldwide. Since the middle of the last century, allergies have increased sharply, especially in the major cities of developed countries. In addition to changing environmental conditions (e.g. higher pollen count), dietary habits and lifestyles, researchers suspect that this trend is also based on the sharp rise in hygiene standards (“hygienic hypothesis”), which can make the “inexperienced” immune system more sensitive to allergens.

Most changes in the environment also affect human bacterial colonisation (e.g. skin, mucous membranes, intestines). While the intestinal flora of primitive peoples, such as those in the Amazon region, comprise a wide variety of intestinal germs, the intestinal flora of people from developed countries has already lost 40% of its biodiversity. Studies indicate that a high microbial diversity in the intestinal flora (mouse model), as well as in the environment (e.g. children living on farms), is associated with a lower risk of allergic diseases, such as asthma or hay fever.

The composition of our intestinal flora has been affected not only by the rise in hygiene standards, but also by changed dietary habits. Ready meals and industrially processed foods often contain preservatives that kill the microorganisms in the food – our immune system is less exposed to germs and can thus become more susceptible to allergies.