Keep Taking Your Fish Oil
The mass media flew into action in early July reporting titillating headlines related to a paper by Theodore Brasky, PhD, and his colleagues at the Ohio State University Comprehensive Cancer Center suggesting a slight link between plasma levels of long-chain omega-3 fatty acids and prostate cancer risk.
Despite the remark within the study manuscript by Brasky and his team that “a lack of coherent mechanism has led authors of previous studies, including us, to consider these findings suspect,” mainstream media outlets were quick to launch attention-grabbing headlines such as “Omega-3 Supplement Taken By Millions ‘Linked To Aggressive Prostate Cancer’,” and “Hold the Salmon: Omega-3 Fatty Acids Linked to Higher Risk of Cancer.”
Alas, this study wasn’t about fish oil supplementation or even eating meaningful amounts of fish in the diet. It was about a single blood test that measured plasma levels of long-chain omega-3s in men up to six years before they were diagnosed with prostate cancer. However, plasma fatty acid levels are highly variable and fluctuate widely depending on short-term dietary composition. In fact, consuming a single meal containing fatty fish hours before testing completely skews the results.
Flawed and inconsistent
Brasky’s findings run counter to copious evidence indicating that omega-3s protect against prostate cancer, not cause it. When a study draws a conclusion inconsistent with much of the existing scientific literature, one has to ask why.
In this case, a reason for these atypical findings may be neglect for baseline characteristics of study participants, which could have dramatically impacted the results. For example, the authors did not control for baseline prostate specific antigen (PSA—a prostate cancer blood marker) levels between case and control subjects in the study. This appears to be a significant methodological flaw as 41.1 percent of men who developed prostate cancer had a relatively high baseline PSA of ≥3 ng/mL compared to only 7.3 percent of those who remained cancer-free.
Regardless of long-chain omega-3 status, or any nutritional biomarker, it is clear that the group with higher baseline PSA levels would have higher prostate cancer incidence. If the authors had controlled for baseline PSA values, the results of this study may have been very different.
Trivial difference in omega-3 levels between groups
The difference in plasma omega-3 fatty acid levels between the study subjects with cancer and without cancer was miniscule: 4.66 percent vs. 4.48 percent. Although the very slight difference in results (0.18 percent) reached mathematical significance due to the number of subjects enrolled, it is not likely to be biologically significant.
The difference was so trivial, and plasma fatty acid levels change so rapidly with diet, that if a man ate a tiny amount of fatty fish the night before, he could have fallen into the higher omega-3 group even if he never ate fish again.
Data indicate that supplementing with about two grams of omega-3 fatty acids from fish oil leads to an increase in the plasma omega-3 percentage from about four percent at baseline to 9.5 percent after eight weeks. It therefore appears that virtually all of the subjects in Brasky’s analysis had insufficient omega-3 levels, were likely not supplementing with fish oil, and did not eat meaningful amounts of cold-water fish.
In the bigger picture of fatty acid physiology and prostate cancer biochemistry, there was virtually no difference in omega-3 levels in men who developed prostate cancer compared to those who did not.
The take-home message
Although popular media outlets created startling headlines based on this flawed study, the reality is that an overwhelming body of evidence suggests that ensuring adequate intake of omega-3 fatty acids is likely to confer numerous health benefits, including cancer prevention. In fact, in a prostate cancer intervention trial, men taking fish oil supplements had less proliferation of cancerous tissue than those that were not supplementing. Moreover, the numerous flaws in the Brasky paper deal a significant blow to its conclusions and render them suspect at best.
Flawed studies will continue to be published, and the mass media will continue to incite panic and confusion by failing to diligently analyze the content upon which they’re reporting. As for us, we’re going to continue taking our omega-3 fish oil supplements.