Ask your grandparents. It is likely that when they were children, they probably had never heard about anyone being allergic to milk or to peanuts. And having asthma was almost incidental. And what about now? One can bet for sure you know people with asthma or atopic dermatitis. Allergic diseases are more and more on the rise and indeed they have been over the last few decades. There have been several attempts to explain the reason why, but only recent research has been able to identify the crucial factor: microbiota.

As we have already explained in this blog, gut microbiota are in charge of training the immune system. When there are alterations in the composition of our gut microbiota, consequences may arise. But how? Which are the key factors affecting this relationship between microbes and health? And can we restore gut microbiota functionality and improve immune system response?

Those were some of the questions a team of researchers in Spain, led by Hospital Clínic and August Pi i Sunyer Biomedical Research Institute (IDIBAPS) in Barcelona, asked themselves and led them to do a review of the scientific literature published between 1989 and 2017 regarding the association between gut microbiota and allergic diseases. They wanted to know what the scientific evidence was and which factors had already been demonstrated to be linked to the development of allergies.

Here is what they found regarding the link between gut microbiota and allergies. Firstly, they have seen the mode of delivery impacts the establishment of gut microbiota in the infant. C-section or vaginal delivery can produce important differences in the composition of the community of bacteria. The Spanish researchers who did the review reported that children born through C-section have lower levels of some species of bacteria than those born vaginally. And that those differences in the composition of gut microbiota are linked to a higher risk of developing allergic diseases and asthma.

Secondly, diet is a key factor in order to prevent the onset of allergies. Breastfeeding increases the colonization by some beneficial bacteria you may have heard of, such as Lactobacilli and Bifidobacteria. Breast milk, for instance, contains oligosaccharides, a type of complex carbohydrates which are the main food for gut microbiota and that contribute to have a balanced bacterial community able to train the immune system. After the weening, the composition of gut microbiota in babies changes, it becomes more diverse and studies show it is important to follow a diet rich in fiber to nourish beneficial bacteria.

Thirdly, as Pérez-Gordo highlights, the exposure to antibiotics have been demonstrated to be one major causes of gut microbiota imbalances. And it is known now that imbalances are linked to diverse health problems. There is solid evidence the maternal intake of antibiotic during pregnancy increases the risk of allergy in the newborns. And antibiotic during the first month of life has been associated with cow’s milk allergy later on.

Sometimes, there is nothing we can do about the mode of delivery or breastfeeding or even antibiotics intake; think about ear infections, so common in infants; frequently they are bacteria-caused and need to be treated with antibiotics. In this sense, for instance, maybe probiotics could be used to cope with aintibiotics side effect; and that is what the  Spanish researchers have seen: probiotics, prebiotics and synbiotics, which are a combination of prebiotics and probiotics, can be used to restore the gut microbiota and even boost the immune system against allergies.

 

ARTICLE:

Pascal M, Pérez-Gordo M, Caballero T et al. Microbiome and Allergic Diseases. Frontiers in Immunology. 2018; DOI=10.3389/fimmu.2018.01584

Cristina Sáez
Cristina Sáez
Cristina Saez is a freelance science journalist. She works for several media, for instance the Spanish newspaper La Vanguardia, where she coordinates the science section, Big Vang; as well as research centres and scientific societies. She has been awarded for her journalistic work, among others, with the Boehringer Ingelheim Award in Medical Journalism 2015. Follow Cristina on Twitter @saez_cristina