Introduction Anthropogenic airborne particulate matter is associated with ischemic heart disease, while little is known about particles from organic dust.

Objective Pigeon breeders are exposed to high levels of organic dust in the pigeon lofts, and the objective of this study is to investigate the association with myocardial infarction.

Methods We followed 6,256 male pigeon breeders and their 1:30 individually matched referents from 1980 or first year of membership in the Danish Racing Pigeon Association if later, until end of study in 2013. Referents were matched on sex and year of birth and randomly drawn from the general Danish population. Information on hospital-based diagnoses, emigration, death and confounders were obtained by record linkage with Danish national registers. Subjects with a diagnosis of myocardial infarction, or chronic ischemic heart disease prior to start of follow-up were excluded. Stratified Cox regression analyses estimated the hazard ratios (HR) of myocardial infarction, adjusted for occupation and place of residence (urban/rural) at start of follow-up.

Results The incidence rate of myocardial infarction was 507 (per 100,000 person-years) among pigeon breeders and 445 among the referents. The crude hazard ratio was 1.16 (95% CI,1.06–1.26), similar after adjusting for possible confounding variables; 1.12 (95% CI,1.03–1.23).

Conclusion In this study we found an increased risk of myocardial infarction among male pigeon breeders. The excess risk is suggested to be explained by exposure to organic dust, pointing to organic dust being a part of ischemic heart disease aetiology. We partly adjusted for lifestyle factors, but the lack of individual information on ex. smoking and dietary factors is a clear limitation. Thus, findings must be interpreted with caution even if adjustment by occupation and place of residence may have reduced such potential confounding. Future research with more detailed information on organic dust exposure and lifestyle factors is warranted.