Seasonal and allergic symptoms in rural populations
Asthma and hayfever are common diseases in children and adults. There have been dramatic increases in the prevalence of allergic diseases over the last 25 years. Either the environment has become more toxic or the population more susceptible. Concern has been expressed that cultivation of oilseed rape leads to seasonal epidemics of respiratory symptoms in populations living near the crop. In order to investigate this apparently widespread problem a combined epidemiological and environmental study was carried out. A cross sectional study was conducted to determine the prevalence of symptoms in a rape growing area compared with a non-rape area. Detailed environmental sampling and a small case-control study to investigate atopy and bronchial reactivity were also conducted. There have been dramatic changes in the Western diet over the last 30 years, with the diet including progressively less fresh food containing antioxidants. It is possible that these changes have increased the susceptibility of the populations to potentially harmful substances. A case-control study was conducted to test the hypothesis that a diet low in antioxidants is a factor in the expression of allergic diseases. Seasonal symptoms were found to be widespread in both rape growing and non-rape growing areas, with only a very small excess of seasonal symptoms occurring in rape growing areas. Little evidence of allergy to oilseed rape, which is consistent with the low levels of pollen recorded, was found. However, there was an increase in bronchial reactivity during the flowering season, especially among cases. This could be a result of non-specific irritation due to terpenes released from the crop.