The Relationship Between Dietary and Supplemental omega-3 Highly Unsaturated Fatty Acid Intake, Blood and Tissue omega-3 Highly Unsaturated Fatty Acid Concentrations, and Colorectal Polyp Recurrence: A Secondary Analysis of the seAFOod Polyp Prevention Trial

Abstract

Background: The seAFOod randomized controlled trial tested colorectal polyp prevention by the omega-3 (ω-3) highly unsaturated fatty acid (HUFA) eicosapentaenoic acid (EPA) and aspirin. Variable dietary intake of omega-3 HUFAs (also including docosahexaenoic acid [DHA]) and differential EPA capsule compliance could confound analysis of trial outcomes.

Objective: The objective of this study was to investigate the relationship between total (diet and capsule) daily omega-3 HUFA intake, red blood cell (RBC), and rectal mucosa omega-3 HUFA concentrations, and colorectal polyp outcomes in a secondary analysis of the seAFOod trial.

Methods: Individual-participant dietary omega-3 HUFA intake (mg/d) was derived from food frequency questionnaires using the European Prospective Investigation into Cancer and Nutrition-Norfolk fatty acid nutrient database. Capsule EPA intake (mg/d) was adjusted for compliance (capsule counting). Fatty acids were analyzed by liquid chromatography-tandem mass spectrometry (as % of total fatty acids). HUFA oxidation was measured using the HUFA/saturated fatty acid (SAT) ratio. The colorectal polyp detection rate (PDR; % with ≥1 polyps) and polyp number per participant were analyzed according to the change in RBC EPA concentrations during the trial (ΔEPA), irrespective of treatment allocation.

Results: There was a small degree of HUFA degradation over time in RBC samples stored at > -80^oC at research sites (r = -0.36, P<0.001 for HUFA/SAT ratio over time), which did not affect analysis of omega-3 HUFA concentrations. Low baseline EPA concentration, as well as allocation to EPA and % compliance, were associated with a high ΔEPA. Individuals with a ΔEPA value >+0.5% points (ΔEPA_high), irrespective of allocation to EPA or placebo, had a lower PDR than ΔEPA_low individuals (odds ratio: 0.63; 95% confidence interval [CI]: 0.40, 1.01) and reduced colorectal polyp number (incidence rate ratio: 0.74; 95% CI: 0.54, 1.02).

Conclusions: Analysis of the seAFOod trial according to the change in EPA concentration, instead of treatment allocation, revealed a protective effect of EPA treatment on colorectal polyp recurrence (ISRCTN05926847).

Keywords: colorectal cancer; compliance; diet; docosahexaenoic acid; eicosapentaenoic acid.

FIGURE 1

The ratio of HUFAs to saturated fatty acids (HUFA/SAT ratio) in baseline RBC samples from seAFOod trial participants according to the duration of storage at trial research sites at either A) >−80^oC, or B) −80^oC. The HUFA/SAT ratio was calculated as the ratio of the sum of % content values for EPA, AA, n–3DPA and DHA divided by the sum of the % amounts of palmitic acid and stearic acid. Individual data points represent the HUFA/SAT ratio for the baseline RBC sample for every seAFOod trial participant who provided a baseline blood sample regardless of subsequent treatment allocation. Of 463 V1 samples stored at a temperature greater than −80^oC, 333 (72%) samples were stored at −20^oC, 53 (11%) samples were stored at a temperature between −21^oC and −30^oC, and 77 (17%) samples were stored at a temperature between −31^oC and −79^oC. Abbreviations: HUFA, highly unsaturated fatty acid; RBC, red blood cells.

FIGURE 2

Dietary and supplement consumption of omega-3 PUFAs in seAFOod trial participants, according to FFQ and capsule IMP compliance, in relation to RBC omega-3 PUFA concentrations. (A) Overlaid frequency histogram of daily dietary EPA+DHA intake categories in the 4 treatment groups. The dashed line represents the dietary EPA+DHA intake per day (0.45 g/d) equivalent to the UK Government recommendation to eat 2 portions of fish per week, 1 of which should be oily [16]. (B) The relationship between daily dietary EPA+DHA intake and the RBC EPA+DHA concentration at baseline (V1). (C) The relationship between daily dietary EPA+DHA intake measured by the V6 FFQ and the rectal mucosal EPA+DHA concentration at colonoscopy (V6) in participants allocated to placebos only. (D) The relationship between daily dietary EPA+DHA intake at baseline (V1) and at the end of the trial intervention (V6). (E) Profile of IMP capsule compliance in seAFOod trial participants. Percentage compliance across the whole intervention period is expressed as a fraction on the X axis. (F) The relationship between overall EPA+DHA intake (from diet and supplement) and the individual RBC EPA+DHA concentration stratified by treatment arm. Abbreviations: FFQ, food frequency questionnaire; UK, United Kingdom; IMP, Investigational Medicinal Product.

FIGURE 3

The change in RBC concentrations of EPA, DPA and DHA at 6 mo during seAFOod trial participation according to random assignment to EPA or placebo. The difference in omega-3 HUFA concentration after treatment for 6 mo (V4) compared with baseline (V1) (ΔEPA) is plotted at individual participant-concentration according to the baseline EPA value for (A) EPA, (B) DPA, and (C) DHA. Summary curves represent the distribution of data points for participants that received placebo (red) or EPA (blue). The insert box in (A) highlights the few participants who were randomly assigned to placebo but displayed a high ΔEPA value. The dashed line in (A) represents the cut-off ΔEPA value (0.5 % points) used for the treatment-independent analysis of colorectal polyp outcomes according to the ΔEPA value during the first 6 mo of trial intervention. Abbreviation: HUFA, highly unsaturated fatty acid.

FIGURE 4

Multivariate models of (A) colorectal polyp detection rate, and (B) colorectal polyp number in seAFOod trial participants independent of treatment allocation to EPA or placebo. The change in RBC EPA concentration at 6 mo from the baseline concentration (ΔEPA_high; defined as an increase in RBC% EPA concentration >0.5% points) was added to (A) logistic regression, and (B) negative binomial regression models, including sex, allocation to aspirin use, and repeat colonoscopy at baseline as covariables. Abbreviation: RBC, red blood cells.