Why the world is becoming more allergic to food
Around the world, children are far more likely than ever before to develop food allergies.
Inquiries into the deaths of British teenagers after eating buttermilk, sesame and peanut have highlighted the sometimes tragic consequences. Last year, a six-year-old girl in Western Australia died as the result of a dairy allergy.
The rise in allergies in recent decades has been particularly noticeable in the West. Food allergy now affects about 7% of children in the UK and 9% of those in Australia, for example. Across Europe, 2% of adults have food allergies.
Life-threatening reactions can be prompted even by traces of the trigger foods, meaning patients and families live with fear and anxiety. The dietary restrictions which follow can become a burden to social and family lives.
While we can't say for sure why allergy rates are increasing, researchers around the world are working hard to find ways to combat this phenomenon.
What causes an allergy?
An allergy is caused by the immune system fighting substances in the environment that it should see as harmless, known as allergens.
These innocent substances become targets, leading to allergic reactions.
Symptoms range from skin redness, hives and swelling to - in the most severe cases - vomiting, diarrhoea, difficulty breathing and anaphylactic shock.
Some of the most common foods for children to be allergic to are:
- milk
- eggs
- peanuts
- tree nuts (eg walnuts, almonds, pine nuts, brazil nuts, pecans)
- sesame
- fish
- shellfish (eg crustaceans and molluscs)
Where are food allergies most likely to occur?
The frequency of food allergy has increased over the past 30 years, particularly in industrialised societies. Exactly how great the increase is depends on the food and where the patient lives.
For example, there was a five-fold increase in peanut allergies in the UK between 1995 and 2016.
A study of 1,300 three-year-olds for the EAT Study at King's College London, suggested that 2.5% now have peanut allergies.
Australia has the highest rate of confirmed food allergy. One study found 9% of Australian one-year-olds had an egg allergy, while 3% were allergic to peanuts.
The increase in allergies is not simply the effect of society becoming more aware of them and better at diagnosing them.
It is thought that allergies and increased sensitivity to foods are probably environmental, and related to Western lifestyles.
We know there are lower rates of allergies in developing countries. They are also more likely to occur in urban rather than rural areas.
Factors may include pollution, dietary changes and less exposure to microbes, which change how our immune systems respond.
Migrants appear to show a higher prevalence of asthma and food allergy in their adopted country compared to their country of origin, further illustrating the importance of environmental factors.
Some possible explanations
There is no single explanation for why the world is becoming more allergic to food, but science has some theories.
One is that improved hygiene is to blame, as children are not getting as many infections.
Parasitic infections, in particular, are normally fought by the same mechanisms involved in tackling allergies. With fewer parasites to fight, the immune system turns against things that should be harmless.
Another idea is that vitamin D can help our immune system develop a healthy response, making us less susceptible to allergies. Most populations around the world do not get enough vitamin D for several reasons, including spending less time in the sun. In the US, the rate of vitamin D deficiency is thought to have almost doubled in just over a decade.
A newer, "dual allergen exposure" theory, suggests food allergy development is down to the balance between the timing, dose and form of exposure.
For example, the development of the allergy antibodies can take place through the skin, particularly through inflamed skin in babies with eczema.
But it is thought that eating trigger foods during weaning can lead to a healthy response and prevent the allergy developing, because the gut's immune system is prepared to tolerate bacteria and foreign substances, such as food.
This was the basis for King's College London's LEAP Study, which showed about an 80% reduction in peanut allergy in five-year-old children who regularly ate peanut from the year they were born.
This study led to changes in US guidelines about peanut consumption in infancy. UK parents have been advised to consult their GP first.
https://www.bbc.com/news/health-46302780
