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"We have known for a long time that damp and mould will make asthma worse if you already have it," the study’s lead author Dr Caroline Shorter says.
"But this is one of the first studies to show that mould may be actually causing asthma to develop," she said.
Dr Shorter is a research fellow in the He Kainga Oranga, Housing and Health Research Programme at the University of Otago’s Wellington campus.
The major study, published yesterday in the international journal Indoor Air, was funded by the Health Research Council and carried out by undertaken by researchers from the housing programme.
Strong links between asthma and mould were "particularly concerning" given that surveys undertaken by the Building Research Association and others showed that about half of all New Zealanders had mould in their homes. It had also been estimated that about 60%-70% of New Zealand rental accommodation also had mould.
"We urgently need to improve the quality of our children’s home environments," she said.
The study investigated the homes of 150 children who had visited their GPs for their first prescribed asthma medication, and compared them with the homes of 300 matched children who had never wheezed.
"We found that mould and leaks were more likely to be found in the bedrooms and homes of children who had just started wheezing compared to the children who had never wheezed," she said.
Youngsters who had the equivalent of several A4 sheet-sized sections of mould in several places in their bedrooms had a 14-fold increased risk of developing wheezing. New Zealand also had "very high rates of asthma". One in six adults and one in four children were reported to have the condition.
Worldwide prevalence of indoor mould was estimated at 10%-30% of homes, and asthma rates were one in twenty. Ventilating houses for 10 minutes a day, as well as cleaning windows and washing curtains, and heating the house to make it drier could make a "reasonably big difference" to reducing mould and making houses healthier.
Dr Shorter was "very pleased" that the research had been published and said research work had taken "quite a long time" to reach that stage.