Over the past 50 years rapid technological advances and rising standards of living have transformed our lives beyond recognition. But could it be that this frenetic pace of change is linked to the dramatic increase in the incidence of allergies?
In the UK in the 1950’s, 1% or less of the population suffered from asthma or an allergy; by the 1980’s about 10% of the population had an allergy and today some estimates are as high as one in three. There is a clear difference in the incidence of allergies in people living in westernized countries compared to developing countries and similarly allergies are more common in urban than rural areas. A 2013 study found that children and teens born outside the US who immigrated to the US are half as likely to develop asthma and allergies as those who are born in the US; immigrants who are second generation have an identical risk of developing allergy or asthma as US born peers. These facts appear to support the hypothesis that our environment is implicated in the increasing incidence of allergies. Genetics and cultural factors relating to diet and lifestyle are also likely to play a role, but it does seem that something in the environment is causing us to become more allergic.
About 25 years ago, it was thought that the answer lay in the hygiene hypothesis. It was postulated that our environment was too clean. The ‘hygiene hypothesis’ suggested that increased levels of hygiene and cleanliness reduced our exposure to bacteria and lead to a reduction in childhood infections. It was thought that these infections were needed to train the immune system. This led to the idea that we were/are too clean. However, these childhood infections are still most common in the urban areas where the incidence of allergies is highest. The hypothesis has now evolved to become the ‘old friends hypotheses’.
By living a much more rural and outdoor lifestyle, our ancestors were exposed to a wide variety of microbes, the ‘old friends’. Modern lifestyles tend to keep people indoors and increasing numbers of people live in urbanized areas. We no longer have exposure to countless microbes to which people had daily exposure a few generations ago. Studies have shown that the variety of microbes to which people are exposed in the most westernized of countries is far more limited than in developing countries. Could this be the answer?
Indeed, changes to our exposure to these old microbes, be they bacteria, fungi or viruses that forms the core of this new allergy theory. In evolutionary terms – our environment remained relatively unchanged for centuries and it has been revolutionized in only a few decades. The problem is not a lack of exposure to childhood infections but a lack of exposure to those old organisms that we had to tolerate throughout our evolution. It would now appear that these organisms are needed to provide the data that our immune system needs to correctly set up the regulatory pathways – the police force that keeps the immune system in check. While we tend to think of bacteria as harmful pathogens, they are in fact predominantly beneficial to us. We need microorganism to provide essential nutrients, to help us break down food in the gut and to protect us against infection. In fact, exposure to harmless bacteria helps to dampen down the immune system. No one type of bacteria holds the answer – it seems more likely that it is the variety of the micro flora which is important. Without everyday exposure to bacteria – our immune system tends to over react.
Babies are not born with allergies – allergies usually develop during childhood and often in the first few years of life. Research now points to the fact that the first year of life is critical for microbial health. During birth, a baby leaves the virtually sterile environment of the womb and is coated in bacteria, predominantly lactobacillus, as it moves through the birth canal. The natural birthing process appears to be the first step towards a health microbiome. Today however, about 25% of babies in the UK and about 30% in the US (up from 5% in the 1970’s), are born by caesarian or C-section and miss out on this critical first microbiome. These babies are more typically colonized by bacteria found on the skin and hospital surfaces. A large Norwegian study found that babies born by c- section were 52% more likely to be become asthmatic.
Antibiotic use, especially in the first year of life, is also highly predictive for the risk of developing an allergy. While antibiotics have had a dramatic, positive impact on modern health – they kill the harmless normal flora of the gut as well as the pathogens. When babies are exposed to antibiotics early in life and during the critical first year in particular – the antibiotics can wipe out the beneficial natural flora leaving the infant open to colonization by a different and perhaps less broad variety of microbes. One study found that giving babies under the age of one antibiotics, increased their risk of developing asthma by 40%. As with babies born by C-section, wiping out the maturing microbiome with antibiotics can leave the baby open to colonization by a different selection of microorganisms leading the immune system to miss information critical to complete its education. Several studies have shown that the composition of the microbiome of children with allergies is different in terms of composition and diversity to that of healthy children.
But can we change our microbiome? The presence and absence of certain bacteria have been associated with allergies but the ideal composition of the gut has not been defined. Prebiotic and probiotics have been associated with beneficial health effects. Probiotics are food products containing live microorganism such as yogurt and dairy drinks. Prebiotics are the indigestible dietary fibers which can help the natural gut microorganisms to flourish. Many health claims have been associated with probiotics but the most we can say is that they may help to reduce sensitivity to allergens.
The only way to cure or clinically reduce sensitivity to allergens is through very careful and repeated exposure to low doses of the allergen. Several companies, e.g. Stallergenes and ALK Abello, have developed desensitization product to allergens such as pollen, house dust mites and ragweed. These immunotherapies are administered by repeated injections and more recently approved product can be given in tablets or drops under the tongue. French company, DBV Technologies, is showing good success with its novel skin patch to treat peanut allergies.
Based on what we now know – the incidence of allergies is likely to continue to increase unless we become more cognizant of the need to maintain a healthy microbiome particularly in the early stages of life and literally go back to our roots.