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Diesel particulate exposure and diabetes mortality among workers in the Ontario construction trades

The world is experiencing a burgeoning epidemic of diabetes associated with increased rates of overweight and obesity. Evidence has accumulated that obesity is associated with a state of chronic low-grade inflammation and that intracellular signalling pathways activated by inflammatory responses are associated with insulin resistance. 3 Diesel exhaust particulate (DEP) has been shown to increase markers of systemic and pulmonary inflammatory response in volunteers and studies of human bronchial epithelial cells in vitro have suggested that DEP induces proinflammatory substances by activating their transcription. Heavy equipment operators (HEOs) are occupationally exposed to DEP. Should these exposures augment a state of chronic low-grade systemic inflammation, then these workers might be at increased risk of diabetes. In a previous analysis I found that HEOs were at increased risk of heart disease mortality in comparison with other construction workers in Ontario. The present analysis was undertaken to explore the hypothesis that DEP-exposed HEOs would also be at increased risk of mortality from diabetes. The methods were described previously. Nine unions provided 124 000 subjects to the cohort (table 1). Subjects were linked to the Canadian Mortality Registry using probabilistic matching methodology. For the 11 341 subjects linked to the Registry, the date and cause of death were retrieved from the death certificate. Mortality odds ratio methodology, a form of case-control study, was used for the analysis. All subjects were from the cohort, and no external reference population was used. Cases were defined as those subjects in the cohort who died from diabetes. Controls were subjects in the cohort who died from any other cause with the exceptions of lung cancer, mesothelioma and accidents. Individuals who had died from these causes of death were excluded because of the possibility of occupational causation in some of the trades. Subjects were grouped among five-year ‘‘year of death’’ and 10-year ‘‘year of birth’’ categories. Mortality odds ratios were computed with conditional logistic regression, using strata formed by combination of these birth and death year categories. After removal of deaths from lung cancer, mesothelioma and external causes there were 7878 deaths for analysis, of which 159 were attributed to diabetes. The distribution of mortality, by union, is shown in table 1. The mortality odds ratio for diabetes was 1.74 (95% CI 1.15 to 2.64) among the HEOs in comparison to all other trades combined. Heavy equipment operators were thus at increased risk of mortality from diabetes in comparison with members of the other construction trades unions. This observation is consistent with the hypothesis that exposure to DEP increases the risk of diabetes, secondary to an increase in systemic inflammation following deposition of DEP in the lungs. It is also possible that this relation was largely, or entirely, the result of confounding by body weight and lower physical activity. In comparison with the other trades, HEOs have a largely sedentary occupation and may have a higher prevalence of obesity. Given the increasing prevalence of diabetes and wide-scale exposure to vehicle exhaust in the environment, further investigation of the role of air pollutants in the development of diabetes is worthwhile. Before any conclusions about the causal influence of DEP and other pollutants can be drawn, it will be necessary to measure and control for confounders such as body mass index, physical activity level and smoking. In the meantime, it would be worthwhile to counsel heavy equipment operators about the observed risk and to encourage weight control and exercise.