Social predictors of adult asthma: a co-twin case-control study

Background-Environmental factors are needed to explain the observed increas e in the prevalence of asthma during recent decades, despite the existence of a recognised genetic component in asthma. A co-twin case-control study w as undertaken to examine possible social risk factors for asthma. Methods-Asthma diagnoses were based on register data of reimbursed asthma m edication. During 17 years follow up of the Finnish twin cohort, 262 twin p airs discordant for incident asthma were identified. Conditional logistic r egression for 1-1 matched data was used for risk calculation. Results-The atopic twin had an increased risk of asthma compared with the n on-atopic co-twin (RR 2.91, 95% CI 1.81 to 4.68). The more educated twin ha d a decreased risk of asthma compared with his/her twin sibling with less e ducation (RR 0.45, 95% CI 0.23 to 0.86), and the twin who participated in c onditioning exercise had a decreased risk of asthma compared with the more sedentary cotwin (RR 0.55, 95% CI 0.34 to 0.88). Conclusions-In addition to allergic diseases, educational level and physica l activity are associated with adult onset asthma, which indicates a role f or factors associated with life style.