Does fish oil consumption have positive effects on the survival of cancer patients?

Fish and omega-3 polyunsaturated fatty acids (PUFA) have been suggested to play a role in improving cancer prognosis. However, results from epidemiological studies remain inconsistent. A new systematic review was aimed at creating clarity by assessing the association between dietary fish and/or omega-3 PUFAs intake and cancer prognosis. For this purpose, the authors conducted a meta-analysis of observational studies.

A systematic search of related publications was performed using PubMed and Web of Science databases. Hazard ratios (HR) and 95% confidence intervals (CI) were extracted and then pooled using a random-effect model. Potential linear and non-linear dose-response relationships were explored using generalized least squares estimation and restricted cubic splines.

As a result, 21 cohort studies were included in the analysis. Compared to the lowest category, the highest category of fish intake was associated with a significant lower mortality in patients with ovarian cancer (n = 1, HR = 0.74, 95% CI: 0.57-0.95) and overall cancer (n = 12, HR = 0.87, 95% CI: 0.81-0.94). Marine omega-3 PUFAs intake rather than total omega-3 PUFAs intake showed significant protective effects on survival of overall cancer (n = 8, HR = 0.81, 95% CI: 0.71-0.94), in particular prostate cancer (n = 2, HR = 0.62, 95% CI: 0.46-0.82).

Yes, correlation is not causation, I know. This is all the more important, as the mechanism of action of PUFAs in relation to cancer seems speculative at present. On the other hand, causality is rendered more likely by a dose-response meta-analysis. It indicated a nonlinear and a linear relationship between fish intake, as well as marine omega-3 PUFAs intake, and overall cancer survival, respectively.

Thus I feel that the conclusion drawn by the authors is reasonable: our analysis demonstrated a protective effect of dietary fish and marine omega-3 PUFAs consumption on cancer survival.