Factors associated with bronchial hyperresponsiveness in Australian adults and children.

To accurately assess putative risk factors for bronchial hyperresponsiveness (BHR), we have used multivariate models to analyse data from 4,366 children living in four regions and from 878 adults. A standard protocol was used to measure bronchial responsiveness to histamine. The prevalence of BHR was high at 7-9 yrs (16-18%), decreased significantly at 11-14 yrs (7-8%), and then increased in adults (12-14%). Atopy was the most important risk factor for BHR at all ages. In children, parental asthma, early respiratory illness and being born in Australia also had a significant influence, and eating fish more than once a week had a protective effect. No effect of parental smoking, gender or race was found. In adults, BHR was associated with being female and with smoking history. It appears that many factors have a significant influence on the presence of BHR, with environmental factors, particularly atopy, birthplace and diet, being the most important.