Environmental factors associated with allergy in urban and rural children from the South African Food Allergy (SAFFA) cohort

Abstract

The recently published South African Food Allergy (SAFFA) study, indicates a clear rural and urban difference in allergy prevalence within a single country.1,2 Various protective and promoting environmental factors have been postulated to influence food and other forms of allergy. Dietary factors, including the consumption of unpasteurized cow’s milk, fermented milk and the variety of foods introduced during infancy were investigated. The influence of fast food, fried food, and microwaved meat and vegetable consumption on allergy were also assessed. This study also investigates the role of a westernized diet, high in advanced glycation end-products (AGE’s), in allergy prevalence. 398 rural and 1185 urban children (12 months to 36 months of age) were screened for self-reported allergic symptoms, food sensitization, and challenge-proven food allergy. Additionally, a subgroup of children (535 urban and 347 rural) was screened for aeroallergen sensitization. Parents/guardians completed questionnaires on antenatal and post-natal environmental and food exposure, including unpasteurized milk and fermented milk products (‘amasi’). 535 urban and 398 rural participants completed questionnaires on fast food consumption. Overall, higher rates of allergic diseases were reported in rural, as supposed to urban children. In the urban cohort, consumption of ‘amasi’ was associated with lower rates of AR (16.8% vs. 31.3%; p<0.001), AD (21.3% vs. 28.6%; p=0.01) and self-reported asthma (5.3% vs. 11.5%; p=0.003). When compared to rural children, consumption of food containing high advanced glycation end products (AGE’s) was associated with significantly higher aeroallergen sensitization rates in urban children (13.8% vs 2.8%; p<0.01, OR 5.5; 1.6-19.1; p<.0.01). In rural children, high consumption of fried/microwaved meat was associated with food sensitization at 1mm and 3mm with odds ratios of 4.4 (CI 1.5-13.0; p=0.01) and 5.0 (CI 1.2-19.9; p=0.02) respectively. Furthermore, high consumption of fruit and vegetables by rural children were associated with significantly higher rates of self-reported asthma (5.7% vs. 3.6%; p<0.001), food sensitization at ≥3mm (8.9% vs. 2.0%; p=0.01) and food allergy (4.4% vs. 0.0%; p<0.001). Early in life, rural exposure protects against some allergies in childhood. Urbanization may hamper exposure to these modifiable, protective elements.