Dietary patterns and colorectal cancer risk in the United Kingdom Women’s Cohort Study

ABSTRACT Background: Some dietary patterns have been associated with colorectal cancer (CRC) in observational studies but the findings are inconclusive. The aim of this study is to explore associations between two dietary patterns, derived using different dietary assessment methods, and risk of CRC. Methods: CRC event data for the UK Women’s Cohort Study were obtained from NHS Digital. Adherence scores to the Mediterranean dietary pattern and to the 2007 World Cancer Research Fund / American Institute of Cancer Research (WCRF/AICR) cancer prevention recommendations respectively were generated. Cox regression was used to estimate hazard ratios (HRs) for CRC risk, for each score separately, using a cohort approach for food frequency data and a case-cohort design for analyses with food diary data. Agreement between scores derived by the two different assessment methods was assessed by weighted Kappa statistics and the Bland-Altman method. Results: After 17 years, 527 CRC cases were observed. The Mediterranean dietary pattern, assessed using the food frequency questionnaire (FFQ), was associated with a decreased risk of CRC. For a 2-point increment in the Mediterranean diet (MD) score, HR 0.88, 95% CI: 0.78, 0.99; Ptrend = 0.03. No evidence of an association was observed when data from food diaries was used for deriving the dietary pattern: for a 1-unit increment in the MD score, HR 0.94; 95% CI: 0.83 to 1.06; Ptrend 0.32. Similarly, no significant associations were observed between higher adherence to the WCRF/AICR guidelines and risk of CRC. For a 1-unit increment in the WCRF/AICR score, HR 0.92, 95% CI: 0.82, 1.03; Ptrend 0.169 for FFQ data whilst HR 1.01; 95% CI: 0.83, 1.24; Ptrend 0.87 for food diary data. The Bland-Altman method showed higher energy intake by the FFQ in comparison to the food diary and agreement between the two methods was slight for the MD score (Κ=0.15; 95% CI: 0.14, 0.16) and fair for the WCRF/AICR score (Κ=0.38; 95% CI: 0.37, 0.39). Conclusion: The Mediterranean dietary pattern is inversely associated with CRC risk whilst a higher adherence to the WCRF/AICR cancer prevention guidelines did not significantly decrease CRC risk in this cohort of British women