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Why have allergies and asthma increased?
- Recent epidemiological studies in the United Kingdom and North America have shown that prevalence rates of food allergy in children have increased. In the United Kingdom the incidence of common allergic diseases has trebled in the last twenty years, to become one of the highest in the world. About 20% of schoolchildren in the UK suffer of asthma, about 15% rhinoconjunctivitis, 10-16% eczema and 6-8% food allergies.
- The increase in peanut allergy has been remarkably high. Recent studies have found that peanut allergy prevalence in the UK is 1.8% and affects 1:50 children in schools.
- There are many theories that try to explain the rise in allergies during the past few decades.
- In general, allergies are associated with the Western style of life. For example, the hygiene hypothesis suggests that the lack of early childhood exposure to infectious agents, gut flora and parasites increases susceptibility to allergic diseases by modulating immune system development.
- It has been argued that either excessive vitamin D or conversely vitamin D deficiency has led to increased allergies. It has also been argued that the decrease in consumption of fresh fruit and vegetables (containing anti-oxidants) in the United Kingdom might account for allergies, particularly asthma.
- The dietary fat hypothesis argues that reduction in consumption of animal fats and corresponding increase in the use of margarine and vegetable oils has led to the increase in allergies.
- There is much debate as to whether early weaning with allergenic foods such as cow’s milk can increase the risk of allergies and asthma. There is some evidence that exclusive breastfeeding for the first four months of life protects against allergies but there is no convincing evidence that allergen avoidance beyond 4 months of age is beneficial. Indeed, it has been argued that early introduction of foods such as peanut may lead to tolerance and protect against of the development of peanut allergy. These theories are currently being tested in the LEAP study (www.leapstudy.com) and the EAT study (www.eatstudy.co.uk).