Cancer incidence and cause-specific mortality in 2663 male submariners with service in the Royal Norwegian Navy between 1942 and 2005: a registry-based cohort study

Objectives A previous cohort study of male Norwegian Navy submariners showed higher overall cancer incidence and lower all-cause mortality than the general Norwegian population. We have extended the follow-up and show more precise estimates through seven decades. Design Historical cohort study using outcome data from Norwegian cancer incidence and cause-of-death registries. Setting Linkage with the outcome registries was performed by means of unique national identification numbers given to all Norwegian citizens. Participants 2663 military men who ever served aboard a Navy submarine between 1942 and 2005. Outcome measures Standardised incidence ratios for cancer and mortality ratios were calculated from national period-specific, gender-specific and age-specific rates. Poisson regression was used to compare cancer incidence in groups with different length of submarine service (>2 years vs <= 2 years). Results The overall cancer incidence was 15% higher than expected from the national rates, with colon, lung, skin (melanoma and non-melanoma) and urinary tract contributing 90% of the excess number of cases. Most of the excess was confined to those with shorter-time service, who also showed elevated risk of alcohol-related cancers. Excess non-melanoma skin cancer was most clearly seen among submariners with >2 years of service. Mortality from all causes combined was lower among submariners than in the general population, due to a markedly low mortality from non-neoplastic diseases and external causes. Conclusions Increased risk of non-melanoma skin cancer was found among submariners with long-term service, and skin exposure to carcinogens in petroleum products was hypothesised as an explanation. Less support for occupational risks was found for other cancers, although the lack of specific exposure data and limited statistical power reduced the possibility of identifying such associations. A 'healthy soldier effect' appeared in the mortality data, mainly restricted to low mortality from non-neoplastic diseases and external causes.