Why has the number of allergy sufferers in the world increased?


Experts still aren’t sure why the number of allergy suffers has risen. However, they do think that if you have more siblings, were born in summer or ate the optimum amount of peanuts in your early childhood you are less likely to develop an allergy.  The University of Manchester has launched an allergy app in the UK. British allergy sufferers can log their symptoms to assist scientists and also view allergy factors for their area such as pollen count. 

The number of people with food, respiratory or skin allergies has increased globally in recent decades and the European Academy of Allergy and Clinical Immunology predicts that by 2025 half of the EU’s population will have an allergy.

Hospital admissions for food-induced anaphylactic shock (an allergic reaction which is potentially fatal) in Australia increased 350% between 1994 and 2005, and in the UK, admissions for food allergies increased 500% between 1990 and 2006.

The growth in sufferers across developed countries isn’t limited to food allergies either. In the UK from the 1960’s to 2007 the percentage of children with eczema and hay fever more than tripled. Moreover, the prevalence of asthma has increased globally by 50% every decade and The Global Initiative for Asthma estimates the condition kills around 250,000 people yearly.

A number of studies have reported possible plateauing or even decline in asthma and eczema in developed countries, but this isn’t certain.

Why have the number of allergy sufferers increased?

There are many theories as to why the number of allergy sufferers has risen globally.

Adnan Custovic, a clinical professor of paediatric allergy at Imperial College London, suggested in the 2007 House of Lords Allergy report that this rise must be due to changing environmental factors, because the genetic background of the population has not changed significantly in the past 50 years.

‘Hygiene hypothesis’
A view of the Mathare Valley slum (Claudio Allia: CC BY SA 3.0)
A view of the Mathare Valley slum (Author Claudio Allia: CC BY SA 3.0)

The ‘hygiene hypothesis’ says those living in cramped, less sanitary conditions are less likely to develop allergies.

It suggests that experiencing fewer infections as a result of a cleaner environment and having less contact with animals, particularly at an early age, can be factors. This is because, even when exposed to non-threatening substances such as pollen, our immune systems aren’t able to tell the difference between harmless and threatening irritants. This is supported by studies that show people living on farms develop fewer allergies, which is thought to be be due to increased exposure to microbes from animals.

Moreover, children who drink raw unpasteurised milk in the first year of their life (more common on farms) are less likely to develop allergies. Some studies have suggested that having a large number of siblings also makes you less likely to develop allergies. This is because if any of your siblings get an infection you are more likely to catch it too, which makes your immune system tougher.

Pregnancy and diet
pregnantwoman2loweres
Pregnant woman (Pexels: CC0 license)

The 2011 EuroPrevall birth cohort study on food allergy (one of the largest studies in the area) found that caesarean births and children from older mothers, over 35, were more likely to be lactose-intolerant.

The quantity of peanuts eaten by the mother during pregnancy is also thought to influence the likelihood of a child developing peanut allergy. Studies from Canada and the US have found that mothers eating too many peanuts increased the likelihood of their child developing a peanut allergy. Mothers eating few during pregnancy and while breastfeeding, reduced the chances.

Peanut allergies in U.S. children doubled from 1997 to 2002, but there is no evidence that the consumption of peanuts or the awareness of food allergies increased as much during this time. Dry-roasting peanuts, which is frequently done in the U.S., UK and Australia, is more likely to create a peanut allergy compared with boiling or frying them instead, as is common in China.

According to Professor Hugh Sampson, from the Mount Sinai School of Medicine, the Chinese introduce peanuts at an early age in a boiled/mushed type form. This is also typical of many African countries, which have very low rates of peanut allergies.

Changing Climate
Melting snow ( Jaymantri: CC0 License)
Melting snow (Author Jaymantri: CC0 License)

When you are born is also thought to influence the risk of contracting a food allergy. Korean and USA studies show that children born between autumn and winter were more likely to develop food allergies at a young age than those born during spring and summer.

On a larger time scale, the rise of average global temperatures and C02 levels in the last century are considered to have contributed to the worldwide increase in asthma prevalence and severity. This is because the subsequentally longer growing seasons and faster plant growth have increased pollen quantities. There also appears to be a link between asthma and hay fever: the 2001 European Community Respiratory Health Survey (ECRHS) found that up to 70% of participants had both asthma and hay fever.

On top of this, according to the National Trust, UK children are spending less time outside than previous generations. This reduces exposure to sunlight, and could be resulting in more cases of vitamin D deficiency. Vitamin D is key for the development of the lungs and immune system.

However, after a paper was published concluding that supplementary vitamin D provided protection against acute respiratory tract infection, the British Society for Immunology (BSI) released a response. Professor Catherine Hawrylowicz of King’s College London and BSI spokesperson, said in a statement, “Observational and experimental studies predict that vitamin D supplementation will reduce susceptibility to acute respiratory tract infections, but clinical trials, which vary greatly in design, have not consistently shown benefit.”

Links with other allergies

According to the National Center for Health Statistics (NCHS), which is part of the United States federal government, “in 2007, 29% of [American] children with a food allergy also reported having asthma, compared with 12% of children without a food allergy” and approximately “27% of [American] children with a food allergy also reported having eczema or a skin allergy, compared with 9% of children with no food allergy”.

Diagnosis

Testing for allergies: skin prick test

Drs Fiona Culley and Akhilesh Jha (Imperial College London) demonstrate one of the main tests used to diagnose allergies, the skin prick test.

The pin prick test allows doctors to easily diagnosis people’s sensitivity to most allergies. Credit: British Society for Immunology

Is it possible that the rise in allergy numbers is down to increased awareness and reporting? While the 2007 House of Lords report acknowledges that increased awareness and improvements in detecting them have lead to an increase in allergies over the last few decades, it still claims allergies are under reported. This is because many studies use hospital admissions for food allergies, but these exclude the majority of allergy sufferers whose symptoms aren’t severe enough for hospital treatment.

According to a senior lecturer in immunology, at The University of Manchester, Sheena Cruickshank: “Overall it’s probably due to there being more allergies rather than increased awareness. Almost certainly increased awareness will factor into that, but I don’t think that can be responsible for the increase that we see, not to the extent that we see.”

Allergy App

#BritainBreathing

British allergy sufferers are to turn citizen scientists in a bid to decode the poorly understood world of seasonal allergies thanks to a free new app. The app – called #BritainBreathing – a collaboration between the Royal Society of Biology, the British Society for Immunology, and The University of Manchester, aims to help the one in four people in the UK who suffer from seasonal allergies like hay fever and asthma.

Britain Breathing is an app which allows users to log their allergy symptoms. Credit: University of Manchester

Britain Breathing is a joint project between the BSI, Royal Society of Biology and the University of Manchester. The researchers have developed an app, Britain Breathing, which allows users living in the UK to submit their allergy symptoms and severity. These are then logged in relation to their location. Sheena Cruickshank, who is working on the project, says it’s very easy to use. You just click on the app, choose a face icon that represents how you are feeling, and then on a sliding scale, for nose, eyes, and breathing, select the symptoms’ severity.

Cruickshank says users don’t need to worry about security issues either. “As soon as you press submit, what it’s doing is capturing the timestamp of when you sent that data, as well as the symptoms that you’ve recorded, and your approximate geo-location. So we can’t say you were standing outside your house in your street, but we will get the sort of rough area that you were in. And that was important, in terms of data and anonymity, that we couldn’t track you down to the precise house and precise street.”

This data is then overlaid with other data sets such as the weather, pollutants and pollens to try and understand what in the environment is causing allergic reactions. The data for the 2016 pilot scheme is already publicly available. This allows you to see where in the UK people experienced different allergic symptoms over the course of eight months.

Symptoms data is important, says Cruickshank, because, “we’ve got diagnosis data, and we’ve got hospitalization data, and we’ve got limited prescription data [but] we don’t have all the other stuff in the middle.’

The Britain Breathing app can be downloaded for free from Google Play for Android and iOS.

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