Objectives Farming as an occupation is considered a risk factor for asthma and reduced lung function. By contrast, living on a farm during infancy has been reported to be associated with lower risk of asthma in adulthood. However, little is known about the association between farming environment during infancy and lung function in adulthood. We aimed to study the prospective longitudinal association between farming environment during infancy and lung function in adulthood.

Design A prospective birth cohort study.

Setting Northern Finland.

Participants 5666 participants born in 1966 were followed up at the age of 31 years.

Primary outcome measures Spirometry at the age of 31 years.

Results To be born into a farmer’s family was associated with higher forced expiratory volume in 1 s (FEV1) (36 mL; 95% CI 6 to 67 mL) and forced vital capacity (FVC) (40 mL; 95% CI 5 to 75 mL) at the age of 31 years. Contact with farm animals during infancy was associated with higher FEV1. No associations were seen with FEV1/FVC (FEV1/FVC ratio). Having dogs in childhood revealed similar associations. There was a suggestive dose-dependent association with the number of animal species during childhood and higher FEV1 and FVC at adulthood, especially among women.

Conclusions Farming environment in early life may have a positive impact on lung function in adulthood.