Objective: A meta-analysis of epidemiologic studies was carried out on lung cancer risk among shipyard, mild steel, and stainless steel welders, and the role of asbestos exposure and smoking was considered.
Methods: The meta-analysis consisted of calculating combined relative risks (RR) and their variances through a logarithm transformation of published RR values and a weighing using the inverted variance of each RR.
Results: The literature provided 18 case-referent and 31 cohort studies. The combined RR values were 1.38 [observed 1028, 95% confidence interval (95% CI) 1.29-1.48] for "all or unspecified welding categories", 1.30 (observed 305, 95% CI 1.14-1.48) for shipyard welders, and 1.35 (observed 173, 95% CI 1.15-1.58) for nonshipyard welders. Similar combined RR values (RR) were observed for mild steel welders (combined RR 1.50, observed 137, 95% CI 1.18-1.91) and stainless steel welders (combined RR 1.50 observed 114, 95% CI 1.10-2.05). No significant heterogeneity was discerned between studies of any welding or study design category. A marked healthy worker effect may also lead to an underestimation of the standardized mortality ratio for lung cancer among stainless steel welders. Furthermore, welders of any category are likely to be exposed to asbestos. Welders also seem to smoke more than the general male population, and therefore the hypothesis of tobacco overconsumption among welders could not be discarded.
Conclusions: A 30-40% increase in the RR of lung cancer among welders cannot be explained by hexavalent chromium and nickel exposure among stainless steel welders. The combination of the carcinogenic effects of asbestos exposure and smoking may account for part of the lung cancer excess observed.