Changes in the relationship between asthma and associated risk factors over fifty years

Childhood asthma is a common condition whose prevalence is changing. We hypothesized that the relationship between asthma and associated risk factors has changed over a 50-year period.

An ecological study design was used. Children aged 8-13 attending schools in Aberdeen city were surveyed on seven occasions between 1964 and 2014. The following were determined: history of asthma, history of eczema, parental smoking, parental asthma, sex and socio-economic status. Analysis was by a structural change model with two knots. The outcome reported was the change in odds ratio between asthma and a given risk factor during a given period.

There were 23,241 questionnaires distributed and 17,439 returned (75%). The odds ratio (OR) for a child with asthma to have eczema increased between 1989 and 1999 by 1.031 [95% CI 1.028, 1.035] and by 1.042 between 2004 and 2014 [1.038, 1.047]. The OR for a child with asthma to have a parent who smoked rose by 1.032 [1.028, 1.036] between 1989 and 1999 and by 1.043 [1.038, 1.047] between 2004 and 2014), and to have a parent with asthma (1.027 [1.022, 1.031] for 1994-99 and 1.042 [1.037, 1.048] for 2004-2014). The OR for a child with asthma being male, but not and being from the most deprived communities, rose between 1989-1999 and 2004-2014.

The relationship between asthma prevalence and particular risk factors changed over the 50-year period of study, and this might reflect changes in children's environment and/or susceptibility.