Background Although asthma is currently the most common chronic disease in childhood worldwide, it is not the key focus of prevention strategies. Diverse modifiable parental and child lifestyle factors has been individually associated with the risk of asthma and allergy symptoms in childhood; however, the quantification of their joint effect is lacking. A healthy lifestyle index (HLI) was developed to examine the combined effect of modifiable lifestyle factors on asthma, rhinoconjunctivitis, and eczema using data from the multicentre International Study of Asthma and Allergies in Childhood (ISAAC) Phase Three. We used this multidimensional lifestyle approach to estimate the impact of potential prevention strategies (mainly recommended for non-respiratory diseases) upon the population burden of asthma, rhinitis, and eczema in childhood.

Methods Information on symptoms of asthma, rhinoconjunctivitis, eczema and several lifestyle factors was obtained from children aged 6–7 years through written questionnaires. The HLI combined five lifestyle factors: no parental smoking, child’s adherence to Mediterranean diet, child’s healthy body mass index, high physical activity and non-sedentary behaviour. The HLI was modelled as a continuous and categorical variable with four categories (0 or 1 factor, 2 factors, 3 factors, and 4 or 5 factors), using 0 or 1 factor as the reference category. The association between the HLI and risk of asthma, rhinoconjunctivitis, and eczema was evaluated using multilevel mixed-effects logistic regression models. To estimate the proportion of cases in the entire study population that could be prevented had all children been following four or all five healthy lifestyle factors (i.e. lowest-risk exposure group), we derived centre-specific population-attributable risk fractions.

Results Data of 70795 children from 37 centres in 19 countries were analysed. Each additional healthy lifestyle factor was associated with a reduced risk of current wheeze (OR=0.87, 95% CI 0.84–0.89), asthma ever (OR=0.89, 95% CI 0.87–0.92), current symptoms of rhinoconjunctivitis (OR=0.95, 95% CI 0.92–0.97), and current symptoms of eczema (OR=0.92, 95% CI 0.92–0.98). Theoretically, if associations were causal, a combination of four or five healthy lifestyle factors would result into a reduction up to 16% of asthma cases (ranging from 2.7 to 26.3% according to region of the world).

Conclusion These findings should be interpreted with caution given the limitations to infer causality from cross-sectional observational data. Efficacy of interventions to improve multiple modifiable lifestyle factors to reduce the burden asthma and allergy in childhood should be assessed.