Respiratory symptoms and obstructive lung diseases in iron ore miners: Report from the obstructive lung disease in northern Sweden studies

This is a population-based study on the prevalence of respiratory symptoms assessed by a mail questionnaire. The objective was to examine if work in an iron mine increased the risk of airway symptoms or obstructive diseases. The exposed group consisted of 114 previous or current male miners. Referents, 2472 males from the province, had never been employed by the mining company or worked as miners. Age, smoking and a family history of asthma were considered as possible confounders. The miners had an increased risk for respiratory symptoms (OR=2.2, 95% CI=1.4–3.1) including recurrent wheeze (OR=2.4, 95% CI=1.5–3.9), longstanding cough (OR=1.8, 95% CI=1.0–3.2), and for physician-diagnosed chronic bronchitis (OR=2.2, 95% CI=1.0–4.5). Attacks of shortness of breath and asthma manifestations were similar between miners and referents. Higher risks in miners were found particularly among the non-smokers for physician-diagnosed chronic bronchitis (OR=9.2, 95% CI=3.0–28) and for symptoms as well. A family history of asthma was less common among miners (9.2% vs. 17%, p < 0.05). We conclude that miners in a modern underground iron mine had an increased risk of respiratory symptoms. In contrast to other studies, this increased risk was particularly found in non-smokers. A family history of asthma may be an important confounder in occupational studies of respiratory diseases.