Daily supplementation of 1 g marine ω-3 fatty acid did not reduce risk for conventional adenomas or serrated polyps, according to a study published by JAMA Oncology.
Although epidemiologic data remain unclear, several prospective studies have indicated that a putative chemopreventive benefit of marine ω-3 fatty acids may act in the early stage of colorectal cancer (CRC) development. In this ancillary study of the placebo-controlled, randomized, clinical vitamin D and omega-3 trial (VITAL), adults in the US general population without cancer or cardiovascular disease (N=25,871) were randomized to receive either 1 g marine ω-3 (n=12,933) or placebo (n=12,938) daily, for a median treatment period of 5.3 years. This study followed the CONSORT reporting guideline for randomized clinical trials. Participants were required to forgo the use of fish-oil supplements, to limit use of vitamin D from all supplemental sources, including multivitamins to 800 IU per day, and to complete a 3-month placebo run-in phase. Participants completed questionnaires and indicated whether they had received a diagnosis of any colorectal polyp in the prior 4 years; researchers acquired medical records only for patients who confirmed the diagnosis. Low-and high-risk subgroups were classified on the basis of the size and histologic features of polyps.
The researchers collected medical records from 35.0% of participants who reported diagnoses of colorectal polyps by the end of the study period (n=999). Diagnosis of conventional adenomas was confirmed in the patients receiving marine ω-3 fatty acids (n=294) and in the placebo group (n=301). Serrated polyp diagnoses were confirmed in patients in the ω-3 group (n=174) and in the placebo group (n=167). Marine ω-3 fatty acid treatment was not associated with risk for either conventional adenomas (multivariable odds ratio 1.05; 95% CI, 0.83-1.15) or serrated polyps (odds ratio 1.05; 95% CI, 0.84-1.29). Null results were found in sensitivity analyses when excluding participants with colorectal polyps that occurred within the first 2 years after the beginning of the trial.
This study was limited by the potential for undiagnosed polyps because the protocol did not mandate regular screening endoscopy. Medical record reviews were possible for only a subset of participants with reported polyps whose physicians recommended surveillance colonoscopy within 5 years. Researchers were also unable to assess a dose-response relationship because only single-dose levels of marine ω-3 fatty acid were used in the trial.
Overall, the researchers discovered thatω-3 supplementation of 1 g per day was not associated with risk of a colorectal premalignant lesion. However, the findings did not rule out a potential benefit of marine ω-3 fatty acid either at higher doses or in high-risk populations, as reported in previous studies of patients with familial adenomatous polyposis14 or with established CRC.
Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.
Song M, Lee IM, Manson JE, et al. Effect of supplementation with marine ω-3 fatty acid on risk of colorectal adenomas and serrated polyps in the US general population: a prespecified ancillary study of a randomized clinical trial [published online November 21, 2019]. JAMA Oncol. doi: 10.1001/jamaoncol.2019.4587