Omega-3 - New Paper: Linked to Cancer Progression

Omega-3 Fats, Angiogenesis, and Cancer: Part I | Perfect Health Diet

New Paper: DHA Linked to Cancer Progression

A new paper, just published yesterday, from “the largest study ever to examine the association of dietary fats and prostate cancer risk” has linked blood DHA levels to cancer risk. Specifically:

Docosahexaenoic acid was positively associated with high-grade disease (quartile 4 vs. 1: odds ratio (OR) = 2.50, 95% confidence interval (CI): 1.34, 4.65) … [4]

This is a large effect: the highest quartile had 2.5-fold higher risk than the lowest-quartile.

That it was the omega-3 DHA specifically, and not polyunsaturated fats generally, that caused the problem, is supported by the fact that (note: edited to correct error in original post – PJ) omega-6 linoleic acid had no effect, and 18:1 and 18:2 trans-fats which are mostly obtained from partially hydrogenated vegetable oils were associated with protection against cancer:

TFA 18:1 and TFA 18:2 were linearly and inversely associated with risk of high-grade prostate cancer (quartile 4 vs. 1: TFA 18:1, OR = 0.55, 95% CI: 0.30, 0.98; TFA 18:2, OR = 0.48, 95% CI: 0.27, 0.84). [4]

People in the top trans-fat quartile had only half the risk of people in the lowest omega-6 quartile. This makes it looks like omega-6-derived trans-fats were protective.

This result conflicts with the idea that the only influence of omega-3 fats is through regulation of inflammation; if so the anti-inflammatory omega-3 would have suppressed cancer. As lead study author Theodore Brasky said in the press release:

“We were stunned to see these results and we spent a lot of time making sure the analyses were correct,” said Brasky, a postdoctoral research fellow in the Hutchinson Center’s Cancer Prevention Program. “Our findings turn what we know — or rather what we think we know — about diet, inflammation and the development of prostate cancer on its head and shine a light on the complexity of studying the association between nutrition and the risk of various chronic diseases.”

Angiogenesis A Possible Pathway

Angiogenesis is very important for cancer progression. Cancers need to form angiogenic vessels if the tumor is to be able to grow beyond about 0.5 mm (0.02 inch) in diameter.

Indeed, angiogenesis seems to be a controlling factor for cancer mortality risk. It is believed that 50% of adults over age 40, and 100% of adults over age 70, have microscopic cancers. However, most tumors never develop an ability to induce angiogenesis and thus the tumors never grow beyond 0.5 mm and cause no observable disease.

Dietary factors that promote angiogenesis favor cancer progression, and anti-angiogenic factors tend to prevent cancer progression. Diet seems to be crucial for cancer prevention. Here is a TED video by Dr. William Li discussing the link between angiogenesis, dietary influences upon angiogenesis, and cancer.

Conclusion

So far, we’ve set the stage. On Thursday I’ll discuss a mechanism by which excessive DHA intake may promote angiogenesis. If this mechanism is important, then excessive fish oil or DHA supplementation may act as a major cancer-promoting food.

UPDATE: The next post in this series: Omega-3s, Angiogenesis and Cancer: Part II

References

[1] Nanji AA et al. Dietary saturated fatty acids: a novel treatment for alcoholic liver disease. Gastroenterology. 1995 Aug;109(2):547-54. http://pmid.us/7615205.

[2] Church MW et al. Excess omega-3 fatty acid consumption by mothers during pregnancy and lactation caused shorter life span and abnormal ABRs in old adult offspring. Neurotoxicol Teratol. 2010 March – April;32(2):171-181. http://pmid.us/19818397.

[3] Szymczak M et al. Modulation of angiogenesis by omega-3 polyunsaturated fatty acids is mediated by cyclooxygenases. Blood. 2008 Apr 1;111(7):3514-21. http://pmid.us/18216296.

[4] Brasky TM et al. Serum Phospholipid Fatty Acids and Prostate Cancer Risk: Results From the Prostate Cancer Prevention Trial. Am. J. Epidemiol. April 24, 2011 DOI: 10.1093/aje/kwr027 (Will be at http://pmid.us/21518693.)