Cancer incidence among seafarers and fishermen in the Nordic countries

Our plain-English summary of Cancer incidence among seafarers and fishermen in the Nordic countries, by K. Ugelvig Petersen, E. Pukkala, J.I. Martinsen, et al (Scandinavian Journal of Work, Environment & Health, 2020).

The study

• Authors: K. Ugelvig Petersen, E. Pukkala, J.I. Martinsen, E. Lynge, L. Tryggvadottir, E. Weiderpass, K. Kjærheim, S. Heikkinen, J. Hansen
• Journal: Scandinavian Journal of Work, Environment & Health
• Published: 2020;46(5):461-468
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives Maritime workers may be exposed to several occupational hazards at sea. The aim of this study was to assess cancer incidence among seafarers and fishermen in the Nordic countries and identify patterns in morbidity in the context of existing studies in this field. Methods A cohort of 81 740 male seafarers and 66 926 male fishermen was established from census data on 15 million citizens in the five Nordic countries. Using personal identity codes, information on vital status and cancer was linked to members of the cohort from the national population and cancer registries for the follow-up period 1961-2005. Standardized incidence ratios (SIR) were calculated applying national cancer incidence rates for each country and pooling results. Results The overall incidence of cancer was increased among the male seafarers [SIR 1.22, 95% confidence interval (CI) 1.19-1.23]. Significant excesses were observed for multiple cancer sites among the seafarers, while results for the fishermen were mixed. Lip cancer incidence was increased among both maritime populations. For mesothelioma (SIR 2.17, 95% CI 1.83-2.56 seafarers) and non-melanoma skin cancer (SIR 1.23, 95% CI 1.14-1.32 seafarers), incidence was increased among the seafarers. Conclusion In our cohort, seafaring was associated with a higher overall incidence of cancer compared to the general population. While the majority of cancers could not be linked to specific occupational factors, increases in mesothelioma, lip and non-melanoma-skin cancer indicate previous exposure to asbestos, ultraviolet radiation and potentially also chemicals with dermal carcinogenic properties at sea.

In plain English

This study followed men aged 30 to 64 in Denmark, Finland, Iceland, Norway and Sweden who reported in censuses taken between 1960 and 1990 that they worked as seafarers (81 740 men) or fishermen (66 926 men). The researchers linked the men to national cancer registries for follow-up between 1961 and 2005. They compared observed cancers with the number expected from national rates. For all cancers excluding non-melanoma skin cancer, seafarers had more cancer than expected (standardized incidence ratio, SIR, 1.22, 95% CI 1.19–1.23), while fishermen were close to expected (SIR 1.02, 95% CI 1.00–1.04). Seafarers had 143 mesotheliomas, about twice the expected number (SIR 2.17, 95% CI 1.83–2.56), and the excess was clearest in the later follow-up periods. Fishermen had 26 mesotheliomas, fewer than expected (SIR 0.44, 95% CI 0.29–0.65). Lip cancer was raised in both groups. Asbestos exposure itself was not measured. The authors concluded that the mesothelioma excess among seafarers indicates previous asbestos exposure at sea. They noted that they had no information on lifestyle, specific jobs or length of employment.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Census-based cohort study with linkage to national population and cancer registries. It used standardized incidence ratios (observed versus expected cancers based on national rates), pooled across countries.
• Who was studied: 81 740 male seafarers and 66 926 male fishermen in Denmark, Finland, Iceland, Norway and Sweden, drawn from censuses between 1960 and 1990. They were aged 30–64 years and were followed 1961–2005. Seafarers included officers, machinists, deck and engine room crew, and ship maintenance and repair workers. Fishermen included whale and seal hunters in Iceland and Norway. There were too few women to analyse.
• Exposure: Self-reported occupation as a seafarer or fisherman in a census. Asbestos and other exposures were not measured. The authors discuss asbestos-containing materials on merchant ships as a likely source of exposure.
• Main results:
  • Seafarers: overall cancer incidence was increased, SIR 1.22 (95% CI 1.19–1.23), for all cancers excluding non-melanoma skin cancer.
  • Fishermen: overall cancer incidence was on par with the general population, SIR 1.02 (95% CI 1.00–1.04), for all cancers minus non-melanoma skin cancer.
  • Mesothelioma, seafarers: 143 cases, SIR 2.17 (95% CI 1.83–2.56). Mesothelioma, fishermen: 26 cases, SIR 0.44 (95% CI 0.29–0.65), which was significantly decreased.
  • Mesothelioma among seafarers by follow-up period: 4 cases in 1961–1975, SIR 1.33 (0.36–3.41); 54 cases in 1976–1990, SIR 2.34 (1.76–3.06); and 85 cases in 1991–2005, SIR 2.14 (1.71–2.65). The excess was clearest in the later periods.
  • Lip cancer: seafarers had 185 cases, SIR 1.19 (1.03–1.38). Fishermen had 384 cases, SIR 2.26 (2.04–2.50).
  • Lung cancer: seafarers had 3582 cases, SIR 1.62 (1.57–1.68). Fishermen had 2546 cases, SIR 1.16 (1.12–1.21).
• The authors' conclusion: The authors concluded that seafarers had a higher overall cancer incidence, though most of their cancers were not related to specific occupational factors. In their view, three excesses indicate previous exposure at sea to asbestos, intense ultraviolet radiation and potentially chemical dermal carcinogens: mesothelioma and non-melanoma skin cancer among seafarers, and lip cancer among both groups.
• Limitations the authors state:
  • The census data gave no information on lifestyle, detailed job descriptions or length of employment.
  • Without information on health behavior, an occupational contribution to some cancers (for example lung, kidney, bladder and liver) could not be assessed.
  • Foreign crew members on Nordic fleets were not included, and their cancer pattern may differ from that of Nordic residents.
  • Too few women were in these occupations to draw conclusions about them.
  • With many comparisons, some findings may be due to chance. The authors give the lower non-Hodgkin lymphoma incidence as an example.

Topics

The National Library of Medicine indexes this study under subjects our site covers: The Navy.

Medical terms in this study, explained in our Lexicon: Standardized Incidence Ratio (SIR), Incidence, confidence interval, Mesothelioma, Carcinogenic.

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• Occupational exposures and male breast cancer: A nested case-control study in the Nordic countries — M. Talibov, J. Hansen, et al. (2019)
• Cancer at sea: a case-control study among male Finnish seafarers — H. Saarni, J. Pentti, et al. (2002)
• Heavy metals, welding fumes, and other occupational exposures, and the risk of kidney cancer: A population-based nested case-control study in three Nordic countries — I.M. Michalek, J.I. Martinsen, et al. (2019)

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