The relationship between toluene diisocyanate exposure and respiratory health problems: A meta-analysis of epidemiological studies

Human epidemiological studies have shown inconclusive results over the effects of diisocyanates on respiratory health problems. A meta-analysis combined evidence on the association between occupational asthma (OA), respiratory function, and toluene diisocyanate (TDI) inhalation exposure. Sixty-one articles on occupational toluene diisocyanate exposure were identified via two databases. Fourteen studies were included in the meta-analysis. The Newcastle-Ottawa Scale (NOS) was used to assess the quality of the studies. Odds ratios (ORasthma) for the association between TDI exposure compared to non-exposure and OA were calculated. The difference in mean differences (MD) of forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC), and the annual mean change differences-in milliliters per year (mL/yr)-in FEV1 and FVC pulmonary function between TDI exposed and non-exposed, were calculated. When applicable, a random effects meta-analysis was performed. The overall summary ORasthma for TDI exposed versus non-exposed was 1.18 (95% CI = 0.78-1.79). The summary of the predicted mean percentage difference (MD%predicted) between exposed versus non-exposed was 2.96% for FEV1 and 3.75% for FVC. A very small decrease of 5 mL/yr for FEV1 and 10 mL/yr for FVC, respectively, was observed between the exposed and the non-exposed groups. There was moderate to low heterogeneity between study results, and most studies were evaluated as high-quality. This meta-analysis found no statistically significant adverse association between TDI occupational exposure and OA. No meaningful differences in lung function were detected between exposed and unexposed groups.