That nutrition affects health would not be argued by many, but questions about specific strategies to prevent chronic disease onset or mitigate disease progression do not yield easy answers. The role of diet in lung health, including chronic obstructive pulmonary disease (COPD), asthma and pulmonary function, has been reviewed repeatedly,1^–4 but whether accumulated findings represent causal links remains an open question. Continuing to build the evidence base is critical, and efforts in this direction will contribute to the formulation of well-informed public health programmes and policies to guide individual, group and industry-level decision making.

In this issue of Thorax, Allen et al5 report the results of a meta-analysis of observational epidemiological studies of vitamins A, C and E in relation to asthma over the life course with the purpose of estimating the effect size for each association (see page 610). Their report summarises data from 40 publications, …