High intake of omega-3 fats linked to increased prostate cancer risk

By Peter Wehrwein

The omega-3 fats in fish have been linked to all sorts of health benefits, including protection against prostate cancer. But for the second time in two years, researchers have found a link between high levels of omega-3 fats in the blood and prostate cancer.

The latest report comes from researchers at the Fred Hutchinson Cancer Center in Seattle. Their case-control study compared blood samples from 834 men diagnosed with prostate cancer with samples from 1,393 men who didn’t have the disease. The blood samples had been collected as part of the SELECT trial designed to find out if taking selenium or vitamin E could prevent men from developing prostate cancer. (Selenium had no effect and vitamin E was associated with an increase in risk.)

The researchers tested the samples for their omega-3 content. Men whose blood samples were in the top 25% of omega-3 fat content were 43% more likely to have been diagnosed with prostate cancer than men whose blood samples were in the lowest 25% of omega-3 content. The finding were published online in the Journal of the National Cancer Institute.

The results didn’t differ much when the three different types of omega-3 fats found in fish and fish oil—eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA)—were analyzed separately.

A similar study published two years in the American Journal of Epidemiology used blood samples from a different prostate prevention study. The results of that study didn’t show any correlation between omega-fat levels in the blood and low-risk prostate cancer.

But there was a catch, because men with the highest DHA levels were found to be 2.5 times more likely to have developed high-risk prostate cancer than men with the lowest levels.

Doubt cast on omega-3s and heart disease protection

Recent research has also dented the reputation that omega-3 fats have for protecting folks against heart disease.

In May of this year, Italian researchers reported in the New England Journal of Medicine that omega-3 fatty acid supplements did nothing to reduce heart attacks, strokes, or deaths from heart disease in people with risk factors for heart disease.

Late last year, a Harvard study published in JAMA found that fish oil supplements immediately before and after surgery didn’t prevent postoperative atrial fibrillation among cardiac surgery patients.

And a few months before that study, Greek researchers weighed in with a meta-analysis that came to the conclusion that fish oil supplements are useless if you’re looking for protection from heart disease–related death, heart attacks, or stroke.

Could it be fish oil and not fish that’s to blame?

Omega-3s have anti-inflammatory effects, and that’s part of the reason they have been seen as dietary good guys and possibly having an anticancer effect. Why they might have a dark side that increases prostate cancer risk is anybody’s guess.

One important point to keep in mind, though, is that there may be a difference between eating fish and taking fish-oil supplements. Over and over again, nutrition research has shown that diets full of food and drink that supply vitamins, minerals, and healthful fats are correlated with good health, whereas studies of supplements that try to isolate what are believed to be the healthful constituents of the food have consistently been disappointing.

Just to be clear: this latest study correlated blood levels of omega-3 fats to prostate cancer. It wasn’t able to prove that omega-3 fats cause prostate cancer, nor did it go into how those blood levels came about and whether men with high blood levels were big fish eaters, took fish-oil supplements, or both.

We like what our colleague, Dr. Howard Lewine, chief medical editor for Internet publishing for Harvard Health Publishing, wrote about the Fred Hutchinson research:

Despite this one study, you should still consider eating fish and other seafood as a healthy strategy. If we could absolutely, positively say that the benefits of eating seafood comes entirely from omega-3 fats, then downing fish oil pills would be an alternative to eating fish. But it’s more than likely that you need the entire orchestra of fish fats, vitamins, minerals, and supporting molecules, rather than the lone notes of EPA and DHA.

Peter Wehrwein is a freelance writer and editor.