Confronting the allergy epidemic

We are in the midst of an allergy epidemic with one in three people currently experiencing one allergic condition or another during the last year.  A Royal College of Physicians report on allergy in 2003  has been followed by a 2007 House of Lords report. The two reports say essentially the same thing – the UK has the highest level of allergy in the world, both in adults and in children. This includes well known conditions such as asthma, eczema, lung fever and food allergy as well as anaphylaxis, hives (angioedema), drug and wasp/bee allergy. 

These conditions are causing a large unmet clinical need that requires urgent attention.  In addition to better clinical services there needs to be a far greater effort to understand why allergy is so common and increasing and what it is about our Western lifestyle that may be driving it.

Careful population based studies in many countries have discovered that allergy is most common in countries that are English speaking and diminishes as one moves East or South.  There are also higher levels of allergy in cities and urban environments than in the countryside.  So what would account for this?  Exposure to farm animals in early life confers a remarkable protective effect against allergy as does consumption of unpasteurised milk, an anthroposophic lifestyle and living in countries where there is a high incidence of parasite infection.  This link is known as the ‘hygiene hypothesis’ – the idea that being overprotected from infection can actually cause allergy.

Immune triggers: turning them on and off

We now recognise that most allergic disease is caused by a special type of inflammation involving immune cells (called Th-2 lymphocytes) which triggers the formation of the allergic antibody (IgE). When in contact with selective allergens the allergic antibody in turn triggers the release of chemicals that cause allergy symptoms like itching, wheezing or coughing. 

But some products from micro-organisms can help prevent the body from over-reacting in this way.  It has been shown that on livestock farms there are very high levels of bacteria, fungi and viruses that interact with special receptors in the lung, nose, gut and skin to reduce the Th-2 response to allergens.  These ‘pattern (or pathogen) recognition’ receptors also respond to altered gut bacteria.  This demonstrates that in the absence of significant levels of bacteria, fungi and viruses, a link exists between acquisition of allergy and diet. 

In turn, this activation of certain pattern recognition receptors has recently been shown to stimulate a second set of lymphocytes (called regulatory T cells or T regs) that damp down Th-2 responses.  This step can prevent or even reverse allergy.  Tropical parasites are potent inducers of regulatory T cells helping explain the protective effects of some types of parasite infection on allergy in Africa, South-East Asia and South America. 

Triggers from Western lifestyle patterns

The implication of these findings is that changes to our environment in moving from rural to urban lifestyles may be depriving our immune response of the necessary stimulation to prevent allergy. 

We may also be increasing our susceptibility to allergy by greater exposure to domestic chemicals, indoor pollutants, chronic stress, antibiotics and paracetamol in infancy, childbirth by elective Caesarean section and food additives.  Feeding infants with artificial cow milk products can also be a factor.  Together these conspire to generate allergy susceptibility.  The development of vaccines that restore this balance and a move to move natural foods have been shown to help but in order to use these treatments very widely we need much more research evidence.

Vaccine therapy for allergy (immunotherapy) stimulates the generation of new regulatory T cells.  This is a possible explanation of how the treatment works, which has been shown to be effective for hay fever, some drug and insect allergies.

Non-indigenous diets

Another contributing factor to allergy is the exposure of our children and young adults to new foods containing allergens that do not normally exist in the indigenous diet.  In the UK examples include peanuts, kiwi fruit, avocado, papaya and soya as well as a vast range of new drugs.  Our children are receiving these at a very young age before their immune system has developed properly.  Many of these foods cross-react with each other and with certain pollens such as birch. 

Drug allergy is a special problem that can be life threatening and may in part be due to an increased susceptibility of the population because of the increase in the number of people living in urban environments.

Solutions?

We need an integrated approach to allergy prevention and management.  Carefully selected allergen avoidance in those who have allergy demands a clear diagnosis of which allergen(s) are causing the problem.  All too often allergic symptoms are treated with drugs without pursuing the underlying cause.  An emphasis on prevention being better than cure must be the way forward.  A healthy, balanced diet and reduced exposure to aggravating agents such as domestic chemicals and indoor and outdoor pollutants would also seem to be sensible although we do need more evidence in these areas.  Finally regular contact with the countryside, exercise and fresh locally grown food are likely to mitigate against allergy and should be part of the management plan of these conditions.

Allergy is a very good example of where prevention and management can give a high reward.  An integrated approach offers our best chance of coping with the spiralling trend.