The latest edition of Current Allergy & Clinical Immunology, the journal of the Allergy Society of South Africa features a number of excellent articles relevant to food allergy. In one of these articles, Dr Claudia Gray of the Allergy & Asthma Clinic at the Red Cross Children’s Hospital in Cape Town, and Dr Shiang-Ju Kung of the Division of Allergy & Immunology at the Children’s Hospital of Philadelphia is the USA, who is also associated with the University of Botswana, discuss the rapid increase in food allergy that has taken place in most westernised countries and how the incidence of food allergy also appears to be rising in South Africa.
Historically most people working in the field of allergy and immunology believed that black Africans, including those living in South Africa, were much less susceptible to allergies in general and food allergies in particular. It was proposed that black Africans were possibly "protected" against food allergy because of factors such as eating a rural diet and possessing a different and unique microflora in the digestive tract as compared to people living in cities.
In the past decade and a half, the incidence of food allergies has increased dramatically in other countries. For example, peanut allergy has doubled in the United Kingdom (UK) and up to 10% of young children in Australia nowadays test positive to food challenges (Gray & Kung, 2012).
South African studies
In the past, studies conducted in Bloemfontein in the 1980s, Gauteng in the 1990s, Pretoria 2005, and Cape Town in 2008, showed that while many individuals of varying ages (2 months to 24 years) reacted positively to skin prick testing (SPT) for wheat, milk, fish, peanut, soy, and egg, only one patient out of a total of 645 subjects had actual symptoms of a true food allergy (Gray & Kung, 2012).
In view of the dramatic increase in childhood food allergy in other countries, a study was conducted in Cape Town to determine the prevalence of allergy to foods such as cow’ milk, hen’s egg, peanut, cashew nut, soya, wheat and codfish, in 100 randomly selected children suffering from atopic dermatitis. The latter condition is regarded as a risk factor for food allergy, although not all patients develop foods allergy when they have atopic dermatitis.
Trigger foods can vary greatly, including all the above mentioned foods, as well as tomatoes, oranges, pineapple, chocolate and foods or drinks containing sulphur.
The average age of the children in the Cape Town study was 3 ¾ years; 41% were of coloured, and 59% of Xhosa origin. 42% of the patients had one food allergy and 12% had multiple food allergies. Peanuts were the most common trigger (26%), followed by egg (24%). Interestingly, fish (3%) and cow’s milk (2%) allergies were much less common. The authors point out that 36% of the young Xhosa patients suffered from a proven allergy to at least one food. 25% of the Xhosa patients were allergic to egg and 17% to peanuts (Gray & Kung, 2012).
Based on these findings Gray and Kung (2012) concluded that, the prevalence of food allergy is high in this high-risk population of young South African patients suffering from atopic dermatitis (also known as eczema) and that the incidence of such food allergies appears to be equivalent to the incidence found in other westernised countries. Such increases in food allergy have also been recorded in other African countries such as Ghana.
Factors that influence food allergy susceptibility
A variety of factors can play a role in causing specific children to develop food allergies. For example the following may be implicated:
- Exposure to allergens (e.g. peanuts) at a younger age and in greater quantities may be protective against food allergy
- The microflora of the gut (this includes all beneficial and also all harmful or pathogenic bacteria that inhabit the gut)
- Gastric acid (generally speaking individuals with higher gastric acid production are less likely to develop food allergies because the allergens are digested by the stomach acid - the increased use of antacids in infants with reflux can reduce the protective effect of gastric acid)
- Dietary changes (change from a rural high-fibre, low-fat diet to an urban diet which is low in fibre, and high in fat and highly refined carbohydrates and sugar)
- Exposure to infections may help to reduce the tendency to develop food allergies. This is known as the "hygiene hypothesis" which states that the increase in allergic diseases in the western world can be explained by a decrease in infections during childhood. In other words, repeated challenges to the immune system will stimulate a robust anti-inflammatory regulatory network that will protect against food and other allergies in later life (Yazdanbakhsh et al, 2002).
- Eczema and other atopic conditions
- Genetic factors (having one or more parent with other manifestations of allergy (e.g. hay fever), will increase the risk that a child may develop food allergy)
(Gray & Kung, 2012)
So what has changed?
As has so often been the case with the emergence in our African population of other diseases which were hitherto practically unknown, the increase in food allergy among black South African children may be due to the rapid urbanisation and westernisation of this population group. Each one of the above mentioned factors has undergone dramatic changes in the past decade as more and more previously rural people move to towns and cities.
For example, an earlier food intake study found that black infants in 2006 were introduced to peanuts at an earlier age and ate larger quantities of these nuts than the Xhosa children studied recently. It is possible that the former children were given an early opportunity to build up tolerance to peanuts that is no longer part of urban child-rearing.
Rural children are more likely to be born by vaginal delivery and thus to be exposed to the microflora of their mother’s bodies. The increase in the rate of caesarian sections, the changing diet of youngsters living in cities, and the much more frequent use of antibiotics, may all contribute to depriving children from developing a robust and resistant microflora in their digestive systems, which can in turn make them more susceptible to food allergies.
From a dietary point of view, urbanisation and westernisation of our indigenous population had resulted in dramatic changes in food intake. Where Africans once ate diets rich in plant foods with a high dietary fibre content, those living in cities have increased their intake of foods derived from animals and of fat and highly processed carbohydrates. Such changes may be contributing to the surge in food allergy.
It is therefore, feasible that we will be facing an epidemic of food allergy as an increasing number of South Africans move to cities and change their lifestyles and diets. Eating unsifted and unprocessed grains and cereals, legumes, vegetables and some fruit may help to stem the tide of advancing food allergy. And perhaps we should let our children play in the sand again and to have pets, to make them less vulnerable to allergies, as has been suggested by researchers for more than 20 years.
(References: Gray C, Kung S-J, 2012. Food allergy in South Africa: Joining the food allergy epidemic? Current Allergy & Clinical Immunology, 25(1):24-29; Yazdanbakhsh M et al, 2002. Allergy, parasites and the Hygiene Hypothesis. Science, 296(5567):490-494.)
Food allergy and atopic dermatitis