Maternal diet vs lack of exposure to sunlight as the cause of the epidemic of asthma, allergies and other autoimmune diseases.

smoke or mite allergen exposure, which could explain the improvement in respiratory symptoms. These types of study are extremely difficult, expensive and time consuming, but also virtually impossible to blind. Patient reporting bias could explain the soft positive outcomes, especially in conjunction with the low follow-up rate (6 months ,55%, 12 months ,75%). Even if the study is accepted as supporting mould control, we do not know which component of mould control is effective (removal, or fungicide, or increased ventilation , or perhaps all three combined). Or perhaps improving ventilation and reducing humidity is a good thing for respiratory health whatever the mechanism? The answer to this question has been the subject of a truly landmark study from New Zealand 21 which studied 1350 non-insulated homes with low income families. The houses were generally stand-alone wooden homes on piles, with heating of a living room only. Two-thirds of homes had damp and three-quarters had visible mould. The homes had at least one household member with respiratory symptoms in the last year or a history of asthma, pneumonia or chest infections. Homes were randomised to have ceiling insulation installed, draught stopping around windows and doors, and moisture impenetrable barriers fitted below the floors (cost £700/house) or to control. Over 12 months there were substantial (of the order of 50%) improvements in self-rated health, wheezing and reduced time off work and school in the intervention group, with fewer visits to GP and hospital. Visible mould was reduced by 50%. Again it is impossible to fully blind this study, but it was single blind and the size of the study and the size of improvements for a mix of hard and soft outcomes give it great weight. Essentially, the authors have identified an important and cost effective public health intervention. Whether it works by reducing mould exposure or whether mould is a bystander of housing quality is an open question. So there is the challenge for any society with a social conscience. The New Zealand study needs to be reproduced around the world, accounting for local housing conditions and climate, to see if the results are transferable. In New Zealand the intervention not only improves respiratory health in a vulnerable part of society, it actually saves them money. Overall heating costs went down by 20%, and that can't be bad for that other big environmental challenge—outdoor climate change! REFERENCES 1 Chapman MD. Challenges …