The healthy worker effect and incomplete exposure information have been problems in former studies regarding the association between exposure to Portland cement dust and respiratory effects. We included former workers and made an individual estimation of particle exposure to reduce the selection bias in this controlled cross-sectional study on the effects of cement dust exposure on respiratory symptoms and ventilatory function in long-term exposed Norwegian cement plant workers. A total of 119 workers from the largest cement plant in Norway and 50 workers from a nearby control plant, born 1918 to 1938, performed spirometry and gave information on respiratory symptoms in 1998 and 1999. The prevalence of symptoms and mean pulmonary function indices were similar for exposed workers and controls. There was no dose-response-related increase in symptoms or decrease in lung function indices. The estimated power to detect a true difference between forced expiratory volume in one second (FEV1) in the two groups of 0.3l was 0.90, assuming 95% significance level. The prevalence of chronic obstructive pulmonary disease was 14.3% in the exposed group and 14.0% among the controls. These findings do not support the hypothesis that cement dust exposure has a negative impact on lung function or gives an increase in respiratory symptoms.

ObjectivesDeclining participation in epidemiological studies has been reported in recent decades and may lead to biased prevalence estimates and selection bias. The aim of the study was to identify possible causes and effects of non-response in a population-based study of respiratory health in Norway.DesignThe Telemark study is a longitudinal study that began with a cross-sectional survey in 2013.SettingIn 2013, a random sample of 50 000 inhabitants aged 16–50 years, living in Telemark county, received a validated postal questionnaire. The response rate was 33%. In this study, a random sample of 700 non-responders was contacted first by telephone and then by mail.Outcome measuresResponse rates, prevalence and OR of asthma and respiratory symptoms based on exposure to vapours, gas, dust or fumes (VGDF) and smoking. Causes of non-response.ResultsA total of 260 non-responders (37%) participated. Non-response was associated with younger age, male sex, living in a rural area and past smoking. The prevalence was similar for responders and non-responders for physician-diagnosed asthma and several respiratory symptoms. The prevalence of chronic cough and use of asthma medication was overestimated in the Telemark study, and adjusted prevalence estimates were 17.4% and 5%, respectively. Current smoking was identified as a risk factor for respiratory symptoms among responders and non-responders, while occupational VGDF exposure was a risk factor only among responders. The Breslow-Day test detected heterogeneity between productive cough and occupational VGDF exposure among responders.ConclusionsThe Telemark study provided valid estimates for physician-diagnosed asthma and several respiratory symptoms, while it was necessary to adjust prevalence estimates for chronic cough and use of asthma medication. Reminder letters had little effect on risk factor associations. Selection bias should be considered in future investigations of the relationship between respiratory outcomes and exposures.