Cancer incidence and all-cause mortality in a cohort of 21,582 Norwegian military peacekeepers deployed to Lebanon during 1978-1998.

Objective: We investigated cancer incidence and all-cause mortality among 21,582 Norwegian male military peacekeepers deployed to Lebanon during 1978-1998. We also looked at cancer risk according to duration of service in Lebanon, in the occupational groups of cooks and mechanics, and the risk of alcohol- and smoking-related cancers among those who served during high- or low-conflict periods.

Methods: The cohort was followed for cancer incidence and all-cause mortality from 1978 through 2012. Standardised incidence ratios (SIR) for cancer and mortality ratios (SMR) were calculated from national rates for the total cohort. SIRs were calculated according to duration of service; among cooks and mechanics; and according to high- and low-conflict exposure. Poisson regression, expressed as rate ratio (RR), was used to see the effect of duration of service, and of conflict exposure.

Results: A decreased risk was found for cancer incidence overall (1050 cases, SIR=0.90, 95% confidence interval [CI] 0.84-0.95) and for cancers of the prostate (SIR=0.78) and skin (other than melanoma) (SIR=0.58). The incidence of rectal cancer was 73% higher in those who served for 1 year or more than in those with shorter-term service (RR=1.73, 95% CI 1.00-3.02). The cancer risk in cooks and mechanics was within expected values. The risk of lung cancer was higher in the high-conflict exposure group than in the low-conflict exposure group (RR=1.79; 95% CI 1.00-3.18). In the total cohort, all-cause mortality was lower than expected (SMR=0.83; 95% CI 0.78-0.88).

Conclusion: We found a "healthy soldier effect" for overall cancer incidence and all-cause mortality. Service during high-conflict periods was associated with a higher risk of lung cancer than service during low-conflict periods, but this risk was in line with that of the reference population.