Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2019 Aug 8:11:669-682.
doi: 10.2147/CLEP.S207413. eCollection 2019.

Exploring geographical differences in the incidence of colorectal cancer in the Norwegian Women and Cancer Study: a population-based prospective study

Sunday Oluwafemi Oyeyemi  1 , Tonje Braaten  1 , Edoardo Botteri  2   3 , Paula Berstad  2 , Kristin Benjaminsen Borch  1
Affiliations

Exploring geographical differences in the incidence of colorectal cancer in the Norwegian Women and Cancer Study: a population-based prospective study

Sunday Oluwafemi Oyeyemi et al. Clin Epidemiol. .

Abstract

Purpose: Norway has experienced an unexplained, steep increase in colorectal cancer (CRC) incidence in the last half-century, with large differences across its counties. We aimed to determine whether geographical distribution of lifestyle-related CRC risk factors can explain these geographical differences in CRC incidence in Norwegian women.

Methods: We followed a nationally representative cohort of 96,898 women with self-reported information on lifestyle-related CRC risk factors at baseline and at follow-up 6-8 years later in the Norwegian Women and Cancer Study. We categorized Norwegian counties into four county groups according to CRC incidence and used Cox proportional hazard models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for risk factors. We used the Karlson, Holm, and Breen (KHB) method of mediation analysis to investigate the extent to which the risk factors accounted for the observed differences in CRC incidence between counties.

Results: During an average of 15.5 years of follow-up, 1875 CRC cases were diagnosed. Height (HR=1.12; 95% CI 1.08, 1.17 per 5 cm increase); being a former smoker who smoked ≥10 years (HR=1.34; 95% CI 1.15, 1.57); or being a current smoker who has smoked for ≥10 years (HR=1.28; 95% CI 1.12, 1.46) relative to never smokers was associated with increased CRC risk. Duration of education >12 years (HR=0.78; 95% CI 0.69, 0.87) vs ≤12 years, and intake of vegetables and fruits >300 g (HR=0.90; 95% CI 0.80, 0.99) vs ≤300 g per day were associated with reduced CRC risk. However, these risk factors did not account for the differences in CRC risk between geographical areas of low and high CRC incidence. This was further confirmed by the KHB method using baseline and follow-up measurements (b=0.02, 95% CI -0.02, 0.06, p=0.26).

Conclusion: Lifestyle-related CRC risk factors did not explain the geographical variations in CRC incidence among Norwegian women. Possible residual explanations may lie in heritable factors.

Keywords: NOWAC study; colorectal cancer; diet; lifestyle; risk factors; women.

PubMed Disclaimer

Conflict of interest statement

The authors report no conflicts of interest in this work.

Figures

Figure 1
Figure 1
Map of Norway showing the 19 counties and regions.
Figure 2
Figure 2
Multivariable hazard ratios (HRs) and 95% confidence intervals (CIs) of factors associated with colorectal cancer (CRC) incidence at baseline and follow-up with chained multiple imputations, in the Norwegian Women and Cancer study.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. GLOBOCAN 2018. Estimated cancer incidence, mortality and prevalence worldwide in 2018. 2018. Available from: http://globocan.iarc.fr/. Accessed October7, 2018.
    1. WHO. World Health Organisation 2018. Top 10 causes of deaths in high-income countries in 2016. 2018. Available from: https://www.who.int/en/news-room/fact-sheets/detail/the-top-10-causes-of.... Accessed December14, 2018.
    1. NORDCAN. Association of the Nordic Cancer Registries 2017. Cancer statistical fact sheet: Colorectal cancer in Norway. 2017. Available from: http://www-dep.iarc.fr/NORDCAN/English/StatsFact.asp?cancer=590&country=578. Accessed November10, 2018.
    1. Larsen IK, Bray F. Trends in colorectal cancer incidence in Norway 1962–2006: an interpretation of the temporal patterns by anatomic subsite. Int J Cancer. 2010;126(3):721–732. - PubMed
    1. Cancer Registry of Norway: facts on colorectal cancer “Tykk- og endetarmskreft”. 2017. Available from: https://www.kreftregisteret.no/Generelt/Om-kreft/Tykk-og-endetarmskreft/. Accessed July 30, 2019.

LinkOut - more resources