Do Omega-3s Really Cause Prostate Cancer?

You probably know that I’m a big believer in the benefits of fish oil, those omega-3 fatty acids you get from eating oily, cold water fish such as salmon, albacore (white) tuna, mackerel, herring, sardines, lake trout and halibut. Omega-3s are called “essential” fatty acids because they are essential for good health, but our bodies don’t make them so we have to get them somewhere else. Over the years, many studies have suggested that omega-3s reduce inflammation in the body, protect against heart disease, play a key role in brain function, protect against cognitive decline and Alzheimer’s disease, and much, much more.

Given all the good things we know about omega 3s, you may have been surprised recently to hear about a study linking fish oil to prostate cancer – it showed that men who had high blood levels of omega-3s had a prostate cancer risk that was 43 percent higher than men with the lowest levels of omega-3s. The study also showed that men with the highest blood levels of omega 3-s had a risk of aggressive prostate cancer that was 71 percent higher than men with the lowest blood levels of these fatty acids.

That was pretty scary news, especially for men who have been eating a lot of fish or taking fish oil supplements for their heart health. When I actually read the study, I discovered that the findings were not as disturbing as the news stories made them sound. The researchers hadn’t actually compared men who ate fish or took fish oil supplements to men who didn’t eat fish or take supplements. In fact, they had no information at all about the diets of any of the men in the study.

Here’s the story: the researchers, from the Fred Hutchinson Cancer Center in Seattle, looked at blood levels of plasma phospholipid fatty acids found in omega-3s in some men participating in a huge National Cancer Institute (NCI) trial focused on finding out whether supplements of selenium and vitamin E lowered the risk of prostate cancer. More than 35,000 men were enrolled in this trial, called SELECT (for Selenium and Vitamin E Cancer Prevention Trial). SELECT was stopped in 2008 because no benefits were seen. Worse, in this study vitamin E was associated with an increased prostate cancer risk.

The Fred Hutchinson researchers working the omega-3 angle looked at blood samples taken at the beginning of the study from 834 men who later were diagnosed with prostate cancer and 1,393 healthy men matched by age and race to the ones who developed prostate cancer. This kind of study is observational in nature. It may identify an association between prostate cancer and omega-3s, but that doesn’t prove that the omega-3s actually caused the cancer.

The researchers reported that the mean blood level of plasma phospholipid fatty acids were 4.66 percent in the men with prostate cancer and 4.48 percent in the healthy controls, a difference of not quite 0.2 percent, which critics of the study viewed as too small to affect prostate cancer risk.

Some earlier observational studies came to conflicting conclusions about whether omega-3s increased or lowered the risk of prostate cancer, (one showed an increase, another saw a reduced risk and a third found no association at all). Other big epidemiological studies have found either “no association” or linked eating a lot of fish to a big (63 percent!) reduction in prostate cancer deaths.

Guys … don’t give up your fish oil.

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