Research Findings

New discoveries on long chain Omega-3 Fatty Acids and prostate cancer

New discoveries on long chain Omega-3 Fatty Acids and prostate cancer

20 July 2013


1. On the 10th July, 2013, eleven scientists, associated with the Fred Hutchinson Cancer Research Center in San Antonio, Texas, reported that they had once again found an increased prostate cancer risk in men with high blood concentrations of long chain omega-3 fatty acid, specifically DHA.

2. This work was published in the prestigious Journal of the National Cancer Institute.

3.  The study involved 834 men with prostate cancer, of which 156 had high-grade cancer as well as 1393 men who acted as controls.

4. The mean value of the percentage of DHA in controls was 2.91, whereas in low grade cancer this value was 3.01 and in high-grade cancer it was 3.09.

5. When plasma phospholipid fatty acids were compared to prostate cancer risk, by prostate cancer grade, it was found that only DHA correlated significantly with high-grade prostate cancer.

The authors do not report this vital statistic”.

6. The authors state “It is unclear why high levels of long-chain omega-3 polyunsaturated  fatty acids would increase prostate cancer risk, and further study will be needed to understand the mechanisms underlying the findings reported here.”

7. The authors point out that the results were contrary to expectations but were not a novel finding because it has been previously reported in two other studies and now they believe the data strongly suggests that long chain omega-3 fatty acids such as DHA do play a role in prostate cancer.

Position statement by CANSA

1. CANSA regards this publication in a serious light and will continue to focus on it and obtain further information.

2. CANSA wishes to highlight the fact that this study did not involve fish oil supplements. None were given to the participants and no data is published on which fish oil supplements or fish were consumed, if at all. In the light of this fact it is incorrect to conclude that fish oil supplements were involved in prostate cancer in this study.  There is no proof for this at all.

3. CANSA wishes to focus attention on different mechanisms and alternative interpretations  that could have been involved in this study. The higher DHA in some participants could simply be due to a low fat diet because in the study DHA is stated as a percentage of all the fatty acids which means that if the percentage of some fatty acids dropped due to a lower fat diet, then the percentage of others will rise.  In other words, higher concentrations of DHA in some participants could be due to the diet and not necessarily the intake of DHA from fish oil .

There is also evidence that the metabolism of certain poly-unsaturated fatty acids can be influenced by the presence of cancer in a given individual. It was found that the conversion of omega-6 to arachidonic acid was stimulated in human breast cancer tissue. It is conceivable but not proven that prostate cancers could have an influence on the conversion of DHA to EPA. If this process were inhibited it could cause an increase in DHA. In such a case cancer could be the cause of the association between high DHA and prostate cancer and not the result. There is no indication that this possibility was considered  by the authors of the study.

4. CANSA is concerned that the quality of fish oil supplements may be an important factor in these findings. CANSA has commissioned the chemical analyses of 65 different fish oil supplements sold in South Africa and found that many of them contain ethyl esters of fatty acids and are also often oxidised. CANSA is concerned that these chemical changes in the fish oil, which were not there when the oil was fresh, may be involved in the prostate cancer discoveries in America. Because of these considerations, CANSA does not think it is wise to reject all fish oil products at this stage but to rather correspond with the American scientists concerning possible chemical alteration of long chain omega-3 fatty acids as an explanation of what was found.  In other words, CANSA will seek more clarity.

5. CANSA is also concerned that the exact nature of the omega-3-containing products used privately by the participants in the study were not reported or carefully scrutinised. Participants or any consumer could not know whether the supplements they were using contained ethyl esters or were severely oxidised – or not.  CANSA considers this to be a significant weakness in the study and appears to make it almost impossible to find out exactly what source of fish oil or fish the participants were using when and before the study was done. In fact there is no proof at all that a significant number of the participants were using any fish oil products including fish at all. The authors do not report this vital statistic.

6. Many fish oil products, contain ethyl-ester-fatty acids which are semi- synthetic products and not natural. Furthermore such products can be severely oxidised if kept on the shelf for a long time.  The fish oil study done for CANSA focused on these aspects especially and it was found that about 30 of the 64 products had fatty acids oxidised beyond the recommended limit – to a greater or lesser extent.  It is possible that oxidised fatty acids such as DHA may be involved in the formation of prostatic cancer. If this is the case the problem is not the intake of fish oil capsules or eating fish like salmon. The problem is the quality of these products in terms of oxidation. This is a hypothesis and not a fact. Future research is needed to discover if there is any link between oxidised DHA and cancer, especially prostate cancer.

7. It can also be reasoned that if DHA, as such, was carcinogenic for prostate cancer, then individuals and nations eating numerous portions of fish per week, should have the highest prostate cancer rate. There is no evidence for this – the opposite is true. Japanese have higher DHA levels in the blood than Americans (5.94 versus 2.91 per cent fatty acids). Other than suggested by the present study, the Japanese do not have higher levels of prostate cancer. In fact the average rate is 12.6 cases per 100 000 compared to 119 per 100 000 in the US. This is almost 10-times lower and makes no sense of the DHA –prostate -cancer link at all. A major difference between the Japanese and the Americans could be that the Japanese obtain DHA mainly from fresh fish which is quite natural and not overly oxidised.

8. No conclusions can be drawn from the study because as yet it is not known if the DHA is the cause of the prostate cancer or simply associated with it. This study says nothing about cause or fish oil supplements. All that it does is associate a so-called high concentration of DHA with aggressive prostate cancer. Association does not mean cause.

9. It has been argued that the difference in the omega fatty acid concentration between the cancer-free group (4.48%) and the high-grade cancer group (4.71%) is only 0.23 of 1%. This is not strong evidence and begs the question of how strong it really is.

10. CANSA does not recommend that using omega-3 supplements or eating fish or fish products should be stopped at this stage due to the work published.  The jury is out.

11. Nevertheless, CANSA sees this development as a wake-up call for the entire fish oil industry to make sure that the products sold to the public are as fresh and natural as possible.

12. CANSA will continue to monitor this subject both locally and internationally and keep the public informed of any further developments.


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