Endotoxin exposure and lung cancer risk: a systematic review and meta-analysis of the published literature on agriculture and cotton textile workers

Objective To examine the association between exposure to endotoxins and lung cancer risk by conducting a systematic review and meta-analysis of epidemiologic studies of workers in the cotton textile and agricultural industries; industries known for high exposure levels of endotoxins. Methods Risk estimates were extracted from studies published before 2009 that met predefined quality criteria, including 8 cohort, 1 case-cohort, and 2 case-control studies of cotton textile industry workers, and 15 cohort and 2 case-control studies of agricultural workers. Summary risk estimates were calculated using random effects meta-analyses. Potential sources of heterogeneity were explored through subgroup analyses. Results The summary risk of lung cancer was 0.72 (95% CI, 0.57-0.90) for textile workers and 0.62 (0.52-0.75) for agricultural workers. The relative risk of lung cancer was below 1.0 for most subgroups defined according to sex, study design, outcome, smoking adjustment, and geographic area. Two studies provided quantitative estimates of endotoxin exposure and both studies tended to support a dose-dependent protective effect of endotoxins on lung cancer risk. Conclusion Despite several limitations, this meta-analysis based on high-quality studies adds weight to the hypothesis that occupational exposure to endotoxin in cotton textile production and agriculture is protective against lung cancer.