As usual, we don't know as much as we think we do...There’s been a spate of articles recently about a new study about circulating omega 3 fatty acid levels in the blood and an increased risk of aggressive prostate cancer. Many of these articles, written in non-scientific and inflammatory ways, make claims that “fish oil supplements increase prostate cancer risk!”, despite the fact that the original study does not make this claim.
For many people, essential fatty acid supplementation can be an important addition to a healthy diet and lifestyle. Essential fatty acid supplementation, generally in the form of fish oils, have been shown in studies to be beneficial to heart and metabolic health, mood and attention, for healthy fetal development, and as an all-around anti-inflammatory (there are so many studies on the benefits of fish oil supplementation; I only included a small handful here). Fish oils are so effective, that a pharmaceutical company created a synthetic version called Lovaza so that they could sell this as a prescription-only pharmaceutical, used for raising beneficial HDL cholesterol and improving overall heart health.
The current study that has generated so much media attention was the latest data tabulation based on SELECT, the Selenium and Vitamin E Cancer Prevention Trial, a large clinical trial looking at the role of selenium and vitamin E on prostate cancer. The trial looked at men who were taking either supplemental selenium, supplemental vitamin E (dl-tocopherol acetate, the synthetic form of vitamin E), or both in combination. SELECT looked at over 35,000 men over a 7 year period. The original trial found a slight increase in prostate cancer for men who took synthetic vitamin E alone (not in combination with selenium) over a 7 year period. No increase in cancer rates were seen among men taking vitamin E in combination with selenium, and no explanation is given for this discrepancy.
Because so many blood samples were taken for this trial, the data collected for SELECT has been used for a number of other studies, including this most recent analysis on omega 3 levels and prostate cancer. However, because the original study did not control for omega 3 in either supplements or in the diet, there are many unanswered questions about the true impact of fish and fish oil supplements on prostate cancer risk.
This is the second study showing a possible correlation between omega 3 blood levels and aggressive prostate cancer. A study done in 2011 found that higher circulating blood levels of DHA (docosahexaenoic acid, one of several "omega 3 fatty acid" compounds) correlated with increased risk of developing a specific type of aggressive prostate cancer. That same study also found a decreased risk for that type of prostate cancer with higher circulating blood levels of trans-fatty acids (which are known carcinogens). Given the strong and consistent evidence of the profound harm caused by trans-fatty acids, we certainly will not begin to recommend the consumption of trans-fats in prostate cancer prevention, despite these findings! The original conclusion of the study was that the researchers had no idea why they were seeing the correlations they were seeing. In fact, the discussion section of that study states:
“A comprehensive understanding of the effects of nutrients on a broad range of diseases will be necessary before making recommendations for dietary changes or use of individual dietary supplements for disease prevention.” (Brasky et.al. “SerumPhospholipid Fatty Acids and Prostate Cancer Risk.” Am J Epidemiol. 2011;173(12):1429-1439. )
There are also quite a few studies of varying size and quality that show benefits of using fish oils in helping manage and prevent prostate cancer, including a study done on fish oil supplementation and prostate cell growth, another looking at a combination of fish oils and vitamin D in the inhibition of prostate cancer cell growth, and quite a few others. The truth is, the data available is inconclusive at best.
As to the most recent study, there are several weaknesses worth mentioning. These weaknesses include the following:
- The study never isolated the source of the circulating DHA - they never interviewed their test subjects to find out whether they were taking fish oils (and if so, what kind and how much) or eating fish. While the assumption is that the higher DHA levels are due to either supplementation or excessive fish dinners, there may be some other biological mechanism at work here (might there be some unique biological process that occurs during more aggressive forms of prostate cancer whereby the body conserves O3s?). The truth is, we don't know. And neither do the researchers.
- If the men in the study were taking supplemental fish oils, when did they start? Is it possible some of these men began taking fish oils after already receiving a diagnosis of enlarged prostate or prostate cancer? This information is not provided in the study, since the data collection was a study on the role of selenium and vitamin E, both of which were administered to the test subjects. What if some participants, in learning they had an enlarged prostate, began taking fish oil supplements on their own? This becomes the classic "chicken and egg" problem.
- The study doesn’t look at the relationship between omega 3 fatty acids versus any of the other forms of essential fatty acids (omega 6, omega 9, etc). There have been some hypotheses stating that the body requires a balance of these three unique types of polyunsaturated essential fatty acids, and that the balance may be as important as the actual blood levels of any single fatty acid. We know that a percentage of those with prostate cancer had higher DHA blood levels. We know nothing about the blood levels of other essential fatty acids in relation to the elevated DHA.
- If these men were taking fish oils, what was the form of the oil? Triglyceride form or Ethyl Ester form? There are different types of fish oil products out there and they do not necessarily all work the same. The ethyl ester form of fish oils specifically is a processed form of fish oils, and is not the form used by the body. Ethyl esters need to be metabolized into triglycerides in order for the body to make use of the essential fatty acids found in most fish oil supplements, and questions have been raised about how efficient the body truly is at making this conversion. Triglyceride forms of supplemental fish oil do exist, but are more expensive and more difficult to find than the ethyl ester forms.
- How do we know which study to believe? As mentioned earlier, there are multiple contradictory studies regarding fish oil and prostate cancer. The truth is, the data we have available on the relative benefits or harm of circulating omega 3 blood levels in a variety of types of cancer is contradictory and inconclusive.
- Commercially available fish oil products may contain PCBs and other environmental pollutants. Many supplement companies do not utilize third party testing nor guarantee purity and potency standards in their product. While the study may indicate that these participants might have been taking fish oil products (or eating large amounts of fish), how do we know there wasn’t an additional correlation with circulating mercury levels, PCB or dioxin levels, or other carcinogenic environmental contaminants that we have been warned that we might be exposed to if eating contaminated fish or using contaminated fish products? Are we sure the correlation was purely between prostate cancer and circulating omega 3 levels, or might there be an additional one or several correlations that the study did not evaluate?
In summary, while this new study is certainly cause for further research and careful decision-making around the use of such supplements, I do not believe it is necessarily cause for stopping the use of fish oil supplementation all together. General recommendations for those who choose to continue to use fish oils as a supplement to an overall healthy lifestyle include:
- Be sure your fish oil product is from a credible company, one that independently assays their products or uses third party quality testing. Do not “skimp” on quality of a fish oil supplement!
- Do not exceed 3 grams of fish oil per day unless recommended to do so by a licensed health care provider.
- Watch for the amounts of specific types of essential fatty acids in your fish oil supplement. The active constituents in most fish oils include EPA (ecosapentaenoic acid), DHA (docosapentaenoic acid), and occasionally other potent nutrients like vitamins A, D and E. Several commercial products claim "1000 mg of fish oil per capsule" but do not state on their label how much actual EPA, DHA, or other nutrients are present in their product. Any “fish oil” product that does not provide the actual breakdown of specific nutrients is probably a poor quality supplement that does not provide for quality control. Furthermore, the actual study only shows a correlation between circulating DHA levels and prostate cancer, not with other types of omega 3 fatty acids (like EPA). DHA is an important nutrient for brain and nervous system health, and is essential for pregnant women and infants for proper fetal brain development. Its relative risks and benefits in aggressive prostate cancer is not understood at this time. If you are concerned about the role of fish oil in increased risk for prostate cancer but still want to get the benefits of a fish oil supplement, discuss your concerns with a licensed healthcare provider and consider a high quality fish oil with a somewhat lower level of DHA.