It is increasingly recognised that long-term exposure to air pollutants may have an effect on lung cancer mortality rates.
The objective of this study was to investigate the association between the incidence of lung cancer and long-term air pollution exposure in two large Scottish cohorts with at least 22 years of mortality follow-up.
Detailed individual baseline risk factors among 22,000 Scottish participants (aged 35–64) were collected during 1970–1976, and linked to mortality records from the General Register Office for Scotland. Records of black smoke data were obtained from The UK National Air Quality Information Archive. Missing daily observations at the black smoke monitoring sites during the period 1970–1979 were imputed using a log-linear regression model, taking into account day of the week and seasonal effects. The median air pollution levels of the 10 year period at the subjects’ residential addresses were estimated from (inverse-squared distance weighted) geometric mean estimates of the nearby monitoring sites of black smoke. Cox proportional hazards regression analyses were used to investigate the association between exposure and lung cancer mortality for follow-up till 1998.
A substantial amount of exposure data had to be imputed: 162 sites had at least 10% daily black smoke data; but only 67 sites had at least 60% data. Using the latter, the estimated long-term median exposure levels at the participants’ residential addresses ranged from 10.8 to 48.1 μg/m3. More than 1000 people died from lung cancer during the follow-up period from recruitment until 1998. After adjusting for smoking habits, marital status, social class, body mass index and deprivation category, and stratifying the baseline hazard functions by 1 year age groups and gender, the hazard ratio for lung cancer mortality was 1.227 (95% confidence interval, 1.062 to 1.417) for 10 μg/m3increase in average black smoke exposure between 1970 and 1979. Sensitivity analyses of the imputation technique, exposure assignment algorithm, follow-up time, criteria for excluding people who did not live close to a monitoring site, and alternative risk models were conducted.
Exposure to higher levels of black smoke is associated with an increased risk of lung cancer. Few studies have looked at black smoke as a marker for air pollution. Our effect magnitudes are at the higher end of the range reported in previous studies, though it is difficult to make a direct comparison due to the different pollutant and exposure method used. Our results suggest that long term exposure to air pollution may contribute to an increased risk of lung cancer mortality. This project is funded by the UK Department of Health.