Difficult to prevent childhood asthma

Efforts to avoid exposure to house dust mites along with dietary changes in the first few years of life do not prevent asthma in children with a family history of the condition. Sensitisation to house dust mites, and consumption of diets with low amounts of omega-3 fatty acid (such as found in fish oils) relative to omega-6 fatty acid have been linked to asthma. Researchers from the Woolcock Institute of Medical Research in New South Wales, Australia, assessed whether attempts to modify these factors could actually prevent asthma and allergic disease in young children. The study involved 616 children. On a random basis they were allocated to receive a diet rich in omega-3 to relative to omega-6 fatty acids, measures to avoid exposure to house dust mites, both interventions, or no intervention during the first 5 years of life. Of these children, 516 were available for evaluation at 5 years of age.The dust mite avoidance effort involved the use of allergen-impermeable linens and regular washing with an anti-mite detergent. With the diet intervention, parents were encouraged to prepare their children's meals using canola-based oils and give them tuna oil capsules to boost omega-3 levels.Although the dust mite avoidance measure reduced bedding allergen levels by 61 percent, it had no effect on the occurrence of asthma or wheeze. In fact, eczema - another allergic condition - was actually more common in the dust mite avoidance group than in no-intervention group, at 26 percent vs. 19 percent. Similarly, while the diet intervention did succeed in increasing the omega-3 to -6 fatty acid ratio, it did not prevent asthma, wheezing or eczema.Previous reports support the view that, under certain circumstances, asthma can be prevented. However, given the null findings of the above study, the researchers conclude that the most effective, practical forms of early life environmental modification and the circumstances under which it will be appropriate to implement them remain to be established.