Are Fish Oils Harmful To Your Health?

You may have seen last week’s highly publicized study targeting fish and fish oil as a cause of increased prostate cancer. Published in the online edition of the Journal of the National Cancer Institute, the authors state that EPA, DPA and DHA (the fatty acids derived from fatty fish and fish-oil supplements) are associated with a 71 percent increased risk of high-grade prostate cancer, a 44 percent increase in the risk of low-grade prostate cancer, and an overall 43 percent increase in risk for all prostate cancers. These figures are enough to scare any man away from eating even one more salmon dinner.

 

But I believe there is something fishy going on with this study. For years, I’ve recommended eating salmon and other cold-water fish and supplementing with good quality fish oil supplements because I’m firmly convinced of the numerous health benefits provided by the special omega-3 fatty acids found only in seafood. This recent study doesn’t concern me, except that it might keep people from eating fish or taking fish oil.

In my extensive research spanning more than two decades, I’ve collected dozens of studies that prove the value of consuming omega-3 fatty acids, either in the form of fish or fish oil supplements. For prostate health alone, I have a file of at least 20 clinical studies from major medical journals that have found only positive effects of omega-3 fatty acids (in the form of dietary fish or fish oil) on inhibiting and/or suppressing prostate cancer. For example, studies analyzing human tissue and serum samples have shown that the ratio of omega-6 to omega-3 fatty acids is higher in patients with benign hyperplasia as compared to normal tissue, and even higher in prostate cancer patients (Mamalakis G. et al., 2002).

Another very recent study of 2268 men found that while salted or smoked fish may increase the risk of advanced prostate cancer, fish oil consumption may be protective against the progression of prostate cancer in elderly men. In addition, no association was found between overall fish consumption in early or midlife and prostate cancer risk (Torfadottir J. et al., 2013).

The author of the recently published negative study doesn’t confine his attack on omega-3s to prostate cancer. He also mentions an analysis of omega-3 fatty acids showing no benefit at inhibiting all-cause mortality, heart attacks, or strokes. According to the researchers:

“We’ve shown once again that use of nutritional supplements may be harmful,” said Alan Kristal, D.Ph., the paper’s senior author and member of the Fred Hutch Public Health Sciences Division. Kristal also noted a recent analysis published in the Journal of the American Medical Association that questioned the benefit of omega-3 supplementation for cardiovascular diseases. The analysis, which combined the data from 20 studies, found no reduction in all-cause mortality, heart attacks or strokes.”

Apparently, Dr. Kristal is providing us with only with a few negative studies and fails to mention the overwhelming number of positive studies that have taken place over the past several decades. For example, he seems to have overlooked more than 100 studies showing that fish consumption and/or fish oil supplements provide protection against heart disease, as well as all major chronic degenerative diseases. He even failed to mention a significant recent review of current evidence on the influence of omega-3 fatty acids on cardiovascular events published in the British Medical Journal. In this comprehensive analysis, the researchers concluded: “Marine omega-3 fatty acids are effective in preventing cardiovascular events, cardiac death and coronary events, especially in persons with high cardiovascular risk,” (Delgado-Lista J et al., 2012).

Dr. Kristal also failed to mention the findings of the recent breast cancer and omega-3 fats study that I wrote about just a few weeks ago. In this analysis of 21 studies encompassing more than 800,000 participants from Asia, Europe, and the U.S., researchers determined that people who consume higher levels of dietary marine n-3 polyunsaturated fatty acids (PUFAs) have a 14% lower risk for breast cancer than those who consume less. The authors noted that fish (especially salmon, tuna, and sardines) are the most abundant source of marine n-3 PUFAs; fish oil supplements were also considered as sources of these marine fatty acids. In their study, the researchers cite various lab studies suggesting that n-3 PUFAs are the most promising subtypes of dietary fat “to inhibit or curtail carcinogenesis and reduce risk.” It’s important to note that the researchers also determined that alpha linoleic acid (the plant-based source of omega-3 PUFAs) does not provide the same protection (Zheng, et al. 2013).

Despite my critique of Dr. Kristal’s paper, I do not dismiss the results of his study. I carefully evaluate all published research in the field of cancer, nutrition, diet, herbs, and supplements. But even if this study does have some validity, it’s certainly not wise to dismiss the dozens of other studies on prostate cancer and omega-3s that have shown just the opposite effect, or the hundreds of studies that show additional health benefits associated with the omega-3s found in cold water fish and fish oil supplements.

I find the evaluation that Robert Rountree, M.D. made of this study to be very enlightening. In Dr. Rountree’s words:

As you may be aware, an article published in the July 2013 issue of the Journal of the National Cancer Institute suggests there is an association between elevated plasma omega-3 fatty acid levels and a heightened risk of prostate cancer. 

This study must be interpreted with a significant degree of caution for a variety of reasons:

• The data came from what is referred to as a retrospective, nested, case-control study. The data was extracted from another, much larger, previously conducted trial that was not originally intended to examine the relationship between omega-3 fatty acid levels and prostate cancer. In other words, the original study was not designed to determine any of the conclusions reached in the analysis contained in the article.
• The study’s results conflict with the results from other studies that do suggest that omega-3 fatty acids offer a protective benefit against prostate cancer; and these other studies were, in fact, designed to analyze that very outcome. (See link) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3629172/ 
• Identifying one particular physiologic marker in a group of individuals with a given condition – in this case, an elevated omega-3 level in men with prostate cancer – does not prove causation, especially when that marker can be influenced by diet or behavior and is only measured at a single point in time.
• It is also hugely important to realize that the authors of this study did not assess any of the participants’ dietary intake of fatty fish or omega-3 nutritional supplements – the study’s conclusions are based wholly on the results of a single blood test.
• The omega-3 index, which measures both EPA and DHA within red blood cells, is a much more accurate indicator of long-term omega-3 intake and tissue status than is the plasma omega-3 level, which is subject to significant day-to-day variability.
• A number of confounding risk factors might have influenced the purported outcomes in the study, despite attempts by the investigators to account for them:
• Considering the extensive body of literature that supports the anti-inflammatory effects of omega-3 fatty acids, there is no credible biological mechanism, nor is one suggested in the article, that would explain why these essential fatty acids might increase tumorigenesis.

1. 53 percent of the subjects with prostate cancer were smokers.
2. 64 percent of the cancer subjects regularly consumed alcohol.
3. 30 percent of the cancer subjects had at least one first-degree relative with prostate cancer.
4. 80 percent of the cancer subjects were overweight or obese.

Summary:  Given the inconsistent data attributable to omega-3 fatty acids and prostate cancer, and acknowledging the broad range of health benefits that are almost universally accorded to omega-3 fatty acid consumption, it would be premature to stop eating fish or to discontinue taking omega-3 nutritional supplements on the basis of this study.

 

References:

Akinsete, J. et al. (2012) Consumption of high v-3 fatty acid diet suppressed prostate tumorigenesis in C3(1) Tag mice. Carcinogenesis, 33: 140–148.

Apte S. et al. (2013) A Low Dietary Ratio of Omega-6 to Omega-3 Fatty Acids May Delay Progression of Prostate Cancer et al. Nutrition and Cancer. Volume 65, Issue 4, DOI: 10.1080/01635581.2013.775316.

Astorg, P. (2004) Dietary N-6 and N-3 polyunsaturated fatty acids and prostate cancer risk: a review of epidemiological and experimental evidence, Cancer Causes Control, 15, 367–386.

Cavazos, D. et al. (2011) Docosahexaenoic acid selectively induces human prostate cancer cell sensitivity to oxidative stress through modulation of NF-kB. Prostate, 71: 1420–1428.

Chavarro, J. et al. (2007) A prospective study of polyunsaturated fatty acid levels in blood and prostate cancer risk. Cancer Epidemiol Biomarkers Prev, 16: 1364–1370.

Chavarro, J. et al. (2008) A 22-y prospective study of fish intake in relation to prostate cancer incidence and mortality. Am. J. Clin. Nutr., 88, 1295–1303.

Connolly, J. et al. (1997) Effects of dietary fatty acids on DU145 human prostate cancer cell growth in athymic nude mice. Nutr. Cancer, 29, 114–119.

Fradet, V. et al. (2009) Dietary omega-3 fatty acids, cyclooxygenase-2 genetic variation, and aggressive prostate cancer risk. Clin. Cancer Res. 15, 2559–2566.

Hedelin, M. et al. (2007) Association of frequent consumption of fatty fish with prostate cancer risk is modified by COX-2 polymorphism. Int. J. Cancer, 120, 398–405

Hu, Y et al. (2010) Syndecan-1-dependent suppression of PDK1/Akt/bad signaling by docosahexaenoic acid induces apoptosis in prostate cancer. Neoplasia, 12: 826–836.

Kao V. et al. (2005) 15-lipoxygenase metabolites of g-linolenic acid/eicosapentaenoic acid suppress growth and arachidonic acid metabolism in human prostatic adenocarcinoma cells: Possible implications of dietary fatty acids, Prostaglandins, Leukotrienes and Essential Fatty Acids 72, 363–372.

Leitzmann, M. et al. (2004) Dietary intake of omega-3 and omega-6 fatty acids and the risk of prostate cancer. Am J Clin Nutr, 80: 204–216.

Mamalakis, G. et al. (2002) Prostate cancer vs hyperplasia: relationships with prostatic and adipose tissue fatty acid composition. Prostaglandins Leukot Essent Fatty Acids, 66: 467–477.

Ritch, C. et al. (2007) Dietary fatty acids correlate with prostate cancer biopsy grade and volume in Jamaican men. J Urol, 177: 97–101.

Szymanski, K. et al. (2010) Fish consumption and prostate cancer risk: a review and meta-analysis. Am J Clin Nutr, 92: 1223–1233.

Terry, P. et al. (2001) Fatty fish consumption and risk of prostate cancer. Lancet, 357, 1764–1766.

Torfadottir, J. et al. (2013) Consumption of Fish Products across the Lifespan and Prostate Cancer Risk, PLoS One. 2013 Apr 17;8(4):e59799. doi: 10.1371/journal.pone.0059799.

Tzonou, A. et al. (1999) Diet and cancer of the prostate: a case-control studyin Greece. Int. J. Cancer, 80, 704–708.

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Yang, Y. et al. (1999) Comparison of fatty acid profiles in the serum of patients with prostate cancer and benign prostatic hyperplasia. Clin Biochem, 32: 405–409.