To Örebro University

BACKGROUND: The observed association between the parental socioeconomic status (SES, measured as education/income) and asthma or wheezing in offspring may be explained by confounding of unmeasured factors (shared genes and family environment). We aimed to study the association between parental SES and asthma/wheeze using cousin-comparison.

METHOD: Data was collected on individuals born in Sweden 2001-2013. Parental SES (education and income) was gathered from Statistics Sweden. Asthma/wheeze was identified using national health registers. The association between parental SES at birth and incident asthma/wheeze was estimated using Cox regression also comparing differently exposed cousins. The association between parental SES at five years and current asthma was estimated using logistic regression.

RESULTS: Included were 955 371 individuals. Mothers with compulsory school only (lowest education group) compared to those with further education (highest education group) was associated with incident asthma/wheeze below one year of age HRadj=1.45(1.38-1.52) and over one year of age HRadj=1.17(1.13-1.20). The corresponding estimates for the lowest income group were HRadj=1.61(1.54-1.69) and HRadj=0.94(0.92-0.97) respectively. In maternal cousin-comparisons, the associations for asthma/wheeze over one year of age was HRadj=1.21(1.05-1.40) for compulsory school only and HRadj=0.94 (0.84-1.07) for the lowest income group. The ORadj for current asthma at five years was 1.05(1.00-1.11) for mother's compulsory school only and 0.98(0.94-1.02) for mother's lowest income group. Results for estimates were similar for father's SES.

CONCLUSION: We confirm an association between low parental SES (measured as education) and asthma/wheeze. Cousin-comparison suggests that this association is not wholly due to confounding of unknown familial factors, therefore supporting a causal relationship. The relationship between parental income and asthma/wheeze is less clear. This study is important for understanding risk factors for asthma/wheeze and for future prevention strategies. Further research is warranted to investigate the possible mechanisms for association between parental education and asthma/wheeze.