The “allergy epidemic” in the Western world has become a public health crisis, with allergy incidence climbing 20% in the last ten years. The reason behind such a rise might be right under our noses – in fact, researchers suggest it’s in our food, our medicine cabinet and our overly sterile lifestyle.
Up until recently, not even medical practitioners thought twice about prescribing antibiotics, while increasing rate of Caesarean births and large proportion of formula-fed infants have been blamed for particularly common allergies in young children. A growing body of evidence points to our Western life choices, which might be accountable for destroying our natural microbiota and inducing a cascade of adverse health effects.
Why common food products cause allergies in some
90% of food allergies occur in response to eight common types of food, including milk, eggs, shellfish, fish, peanuts, soybeans, tree nuts and wheat. While the immune system should not react to products that ensure our basic nutrition, increasing number of people develop allergies, which usually follow a characteristic pattern. That is, young children tend to develop atopic dermatitis, which is followed by food allergy, allergic rhinitis and asthma later in life. While allergies are often transient in infancy, some, especially those involving peanuts or shellfish, may persist and pose a risk of anaphylactic reaction at all stages of life.
“As specific organisms and their mechanisms of action continue to be discovered, we can expect new therapies emerging in the near future – however, making healthy microbe-friendly decisions may be just as important.”
Specific allergens that irritate the immune system (e.g. milk protein) have been well established, however this knowledge does not bring us any closer to understanding why some people are affected, while others are not. On the other hand, evidence is piling up suggesting the integrity of our immune system relies greatly on our fellow travelers – our microbiome, which might be the key in explaining the rising incidence of allergies.
The role of friendly bacteria in fending off allergies
Recent evidence suggests our natural microbiota may play a central role in preventing food sensitization. A new study, which was published online last month, advocates commensal Clostridia bacteria, which are common colonizers of the gut, are crucial in keeping the lines of communication open between the digestive tract and the immune system. In other words, by promoting a healthy barrier in the intestines, these bacteria ensure that food allergens (such as milk protein) do not reach the circulation where they might trigger the immune system, manifesting in an allergic reaction.
Commensal microbes have also been demonstrated to produce anti-inflammatory molecules, which are active in various regions of the gut, and diverse metabolites produced by certain bacteria, such as short-chain fatty acids, have also been implicated in regulation of the immune response. These findings suggest that microbial diversity is not only crucial to maintain, but certain organisms, such as Clostridia, could give rise to novel immunotherapies.
Antibiotics wipe out protective microbiome
A number of recent studies have demonstrated the link between extensive antibiotic use and allergy prevalence. Researchers suggest that antibiotics are particularly hard on Bacteroidetes and Firmicutes bacteria (famous for diverse Lactobacillus species), which are particularly prevalent in the gut.
Interestingly, the administration of broad-spectrum antibiotics caused new born mice to develop a peanut allergy, which was later relieved by a fecal transplant from unaffected mice; the same protection has been observed when mice were supplemented with Clostridia. Also known as fecal bacteriotherapy, the approach has been successfully used for treating inflammatory disease and recurrent C. difficile infections, especially post antibiotic therapy.
Moreover, antibiotic use before and during pregnancy has been associated with increased risk of cow’s milk allergy in newborns. The same applies for antibiotic use in offspring. Thus, the necessity of antibiotic therapies during pregnancy should be carefully considered, and in cases where they are unavoidable probiotic counter-therapies may be an option.
Natural birth and breastfeeding ensures a healthy microbial ecosystem in infants
Increasing number of elective C-sections and a large proportion of formula-fed infants is probably the next greatest issue accountable for reduced microbiome diversity in babies an young children.
The benefits of breast milk have been well established – it is known to reduce the chance of ear infections, and other infectious diseases later in life, promote a healthy immune system. Exclusive breastfeeding has even been linked to higher IQ scores etc. The reason behind the many health benefits of breast milk is beginning to unravel – researchers now suggest that long-term benefits of breastfeeding may lie in its ability to promote a healthy microbiome in the gut. In fact, another recent study has demonstrated that antibodies present in breast milk promote a diverse community of gut microbes, which are in turn responsible for a healthy immune function in the intestines.
Moreover, a number of studies have looked into the role of natural birth in establishing “starter” microbes, which lead to a diverse microbiome in early infancy. A research, which was conducted in Canada in 2013, has found that natural birth significantly improves microbial richness in young infants (especially compared to elective C-section), while an analytical study a few years back has suggested an increased prevalence of food allergies in infants born by a C-section.
Overall, yhe accumulating body of evidence suggests that the microbiomes of allergic infants differ dramatically from non-allergic ones, and health promoting probiotics are being explored for treatment of the allergic disease. As specific organisms and their mechanisms of action continue to be discovered, we can expect new therapies emerging in the near future – however, making healthy microbe-friendly decisions may be just as important.
Written by Egle Marija Ramanauskaite