Omega-3 Fats & Cancer

Tuesday, January 9, 2007 - 4:01pm

By Donna Feldman, MS, RD

Omega 3 fats are in the nutrition spotlight these days, linked to all kinds of chronic conditions from heart disease to mental illness to cancer. Needed in small amounts by the human body, omega 3 fats have been virtually eliminated from modern diets by food production methods. Few natural food sources of this important fat remain, except for oily fish like salmon and tuna. Cancer researchers only recently started to investigate the possibility that this group of essential fats might have some role to play in prevention or treatment of cancer. So far, most studies are limited to estimating omega 3 intake from diet histories and comparing intake to cancer incidence. This type of study doesn’t always give the most accurate results for intake, and doesn’t address the issue of cancer treatment or omega 3 supplements at all. Some cancer patients and their health care providers are taking matters into their own hands, taking fish oil supplements in an attempt to help fight off cancer. Are they making a good choice?

More fish - less risk
Fish is the main human food source of omega 3 fats. But there is a problem with studies that just look at fish consumption: not all fish are created equal in omega 3 fat content. As Karen Collins, a dietitian with the American Institute for Cancer Research points out, the most popular fish varieties in the U.S. are low in omega 3 fats. This fact complicates conclusions from research that uses fish consumption as a marker for omega 3 intake. In the U.S., fish consumption doesn’t always mean omega 3 consumption. In Northern European countries, where salmon and herring are popular, omega 3 intake from fish is higher, and research findings are more meaningful. Studies comparing populations that eat lots of fish to populations that don’t indicate a trend: more fish, less cancer risk.

Results are encouraging
In one large study, reported in the American Journal of Clinical Nutrition1, almost 50,000 men were followed for 14 years for development of prostate cancer. When researchers looked at intake of the two main fish oils, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), men with the highest intakes had significantly lower risk for cancer, and less risk for advanced cancer.


Intervention studies lacking
As yet there are no reported results from intervention studies with human cancer patients, using omega 3 supplements to prevent or treat existing cancer. This kind of study would be ideal, as the omega 3 intake from supplements could be controlled. Some studies done on animals do show encouraging results. Omega 3 fats seem to have some anti-cancer effect in animal experiments. These studies use special genetically engineered animals, and very specific cancer cell types, so it’s impossible to generalize to human cancer treatment. A colon cancer patient can’t conclude that, because experimental mice implanted with skin cancer cells improved with omega 3 supplements, taking omega 3 supplements will defeat colon cancer.

If there’s one definite thing to say about omega 3 fats and cancer, it’s this: stay tuned. There are many theories as to why omega 3 fats would affect cancer cell growth and proliferation. There is no proof for any of these theories at the moment. Taking omega 3 supplements based on the hope that they will fight cancer should be discussed with your health care team. Omega 3 fats are known to affect other health problems, such as heart disease. The possibility that they can help with cancer is very exciting, but shouldn’t lead anyone to expect miracles.

1 Am. J. Clin. Nutr. 2004;80:204-16