Mendelian Randomization Study for Genetically Predicted Polyunsaturated Fatty Acids Levels on Overall Cancer Risk and Mortality

Background: Observational studies evaluating the link between polyunsaturated fatty acids (PUFA) and cancers have yielded mixed findings. We used Mendelian randomization (MR) to evaluate whether genetic evidence supports a causal role for PUFAs on overall cancer outcomes. Methods: We identified genetic instruments for six PUFAs from previous literature and evaluated their association with overall cancer risk (46,155 cases, 270,342 controls) and cancer mortality (6,998 deaths, 270,342 controls) among the UK Biobank cohort. We used the inverse variance weighted model to combine SNP estimates, and derived log (OR) estimates per SD change in each PUFA. Results: None of the six PUFAs showed association with overall cancer risk or mortality, with narrow confidence interval (CI) ruling out all but very small effects, for example, arachidonic acid (AA) overall cancer risk (OR, 1.02; 95% CI, 1.00-1.03). Sex-specific analysis revealed no associations except alpha-linolenic acid for potentially reducing cancer risk in men (OR, 0.92; 95% CI, 0.86-0.98; P = 0.02); however, this was nonsignificant after multiple testing correction. From individual cancers, only colorectal cancer showed evidence for a causal association for higher AA levels (OR, 1.05; 95% CI, 1.03-1.07), with similar results for the other correlated PUFAs. Conclusions: Our study provides no support for the hypothesis that PUFAs reduce overall cancer risk or mortality. Higher AA levels increased the risk for colorectal cancer. Impact: Our well-powered MR study provides robust causal inferences for the PUFAs on overall cancer risk and mortality. Future larger studies are warranted to replicate the individual cancer findings.