| |
|
|
|
An estimated 40% of the UK population suffers from some sort of allergy. Food allergy occurs in up to 8% of children under the age of 5 years, and two percent of under fives have an allergic reaction to cow’s milk protein. Although around 20% of the adult population believes they suffer from a food allergy, tests suggest that just under two percent of adults have a true food allergy (if we look at those who tested positive for IgE, 3% did ), but up to 50% of the population may have a food intolerance.
In recent years, there has been an increase in reported problems digesting food, such as IBS; but there is no evidence to suggest that there is an actual increase in the number of people who have allergies, or that we are eating more ‘allergenic’ food. That said, the science of allergy has evolved greatly over the last twenty years or so, and, generally speaking, much of the population is more attuned to the way their bodies react to food; we no longer hear about people being ‘bilious’ the way we once did. Public perception of allergy is always greater than the actual incidence; a 1983 US Department of Agriculture report suggested that around half the adult population believed that they, or their children, had some degree of sensitivity to food. The actual incidence of allergy in the general population was under 15%.
Allergy and Intolerance may be caused by many things, but it is certain there is a genetic component involved. For example, 25% of the US population suffers from lactose intolerance. If we look at these numbers by ethnic origin a genetic component is clearer: 79% of the Afro-American population is lactose intolerant, and 90% of the Asian US population is lactose intolerant. As more intermarriage between cultures and races occurs, so the propensity to intolerance may spread.
For all allergies, a clearer genetic picture can be painted
If neither parent has an allergy, any child has a 5% to 15% chance of being atopic (i.e. allergy-prone)
If one parent is atopic, then any child has a 20% to 40% chance of being atopic
If both parents are atopic, then any child has a 20% to 60% chance of being atopic
If both parents are allergic to the same substance, then any child has a 60% to 80% chance of being allergic to the same substance as its parents
If one sibling is atopic, then other children in the same family have a 25% to 35% chance of being atopic, even if their parents are not atopic.
Scientifically speaking, with a food allergy, it’s likely that you’ve got a very permeable epithelium; the cells that divide the gut from the blood stream are more widely spaced, and hence allow food allergens to reach the immune system. With a food intolerance, a severe digestive upset, or a viral illness, may have caused you to be more sensitive to certain foods.
There are reasons why guts become more permeable. Babies, for example, have very sensitive guts, especially when they are aged less than six months. Their first encounters with food can lead to toleration, or, in some rare cases, sensitisation – which is why it is important that children avoid potentially allergenic foods during this period, in order to reduce the possibility of a food allergy later on.
In adults, the picture tends to be more complicated: inflammation due to infection can cause a more permeable gut wall. Moreover, stress can have an effect on the digestive system. Combined allergic reactions can make a reaction more likely, for example, food allergens that are of a similar shape to the allergens in the inhalants. Alcohol, exercise, and hormones can also act as catalysts to the reaction with the allergen, particularly in women, whose hormone levels naturally fluctuate from month to month, as well as throughout their lives.
There is no one simple answer as to why a person may become allergic to a particular food stuff; or why they may suffer from an intolerance to it.
It is possible to ‘grow out’ of an allergy; babies will often outgrow mild food allergies, particularly to milk, wheat, egg and soya before the age of three, and generally before the age of five, particularly if they do not come from an atopic family. Allergies acquired after the gut wall has lost its initial permeability i.e. after the age of three years, are, however, less likely to disappear . Allergies to peanuts, nuts, shellfish and fish are more likely to persist into adulthood. It is estimated that 80% of children who are atopic are allergic to one or two foods.