Fish oil, a popular dietary supplement, may increase the risk of prostate cancer. (Photo: Flickr/Stephen Cummings)

Fish oil and prostate cancer? Experts say the popular omega-3 fatty acids may raise the risk of the most aggressive form of the disease, which affects about 230,000 men every year in the U.S., by 70 percent. The news that fish oil and prostate cancer are linked comes from scientists in Seattle who say that men with the highest traces of omega-3 in their blood were far more likely to develop hard-to-treat, fast-growing prostate tumors.

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"These anti-inflammatory omega-3s were associated with a 43 percent increased risk for prostate cancer overall, and a 71 percent increased risk in aggressive prostate cancer," Theodore Brasky, lead author of the study, told MSN.

The study looked at 2,227 men, 834 of whom had prostate cancer. Of the patients with prostate cancer, 156 of them had a more aggressive form of the disease.

How much fish oil do the researchers from the Fred Hutchinson Cancer Research Centre in Washington say is enough to increase men's risk of developing prostate cancer? Just one supplement a day, or three to four meals of fish like salmon and mackerel each week.

Fish oils, which are touted for their health benefits, including their anti-inflammatory properties, may have properties that are not well understood. "In high doses, [omega-3 fatty acids] could cause oxidative stress, which can lead to DNA damage, possibly increasing the risk for prostate cancer," MSN reports.

The Daily Mail reports that omeg-3 fish oils are one of the most popular supplements in the UK, and account for one-fifth of dietary supplement sales. Americans also love their fish oil, and spend a whopping $1 billion a year on fish oil supplements. People take them because they are thought to lower blood pressure and to decrease the risk of heart attack, as well as ward off Alzheimer's disease.

But not everyone agrees with the researchers from Seattle. Some are saying the correlation between omega-3s and prostate cancer doesn't prove causation. "The fact is, don't overdose on omega-3 supplements and don't eat a pound of salmon a day," Jason Blaha, who runs a YouTube channel on diet and health called Ice Cream Fitness, says in a video in which he addresses the fish oil-prostate cancer claim.

According to ABC News, the original study from which researchers in Seattle mined their data from was not designed specifically to investigate the link between fish oils and prostate cancer. From The Columbus Dispatch:

This study wasn't a randomized, double-blind study designed specifically to test for any relationship between fish oil and prostate cancer. That's the gold standard. Instead, the researchers went back and looked at blood analysis in a group of men who were part of a major study looking at the effects of selenium and vitamin E in prostate cancer.

"This is not proof that omega 3's cause prostate cancer," ABC News Chief Health and Medical Editor Dr. Richard Besser said. Besser said that the study should not make people stop taking fish oil necessarily, but it should highlight the fact that the best diet supplements don't come in pill form; the best resource for vitamins and oils is solid food.

Ice Cream Fitness reports in a video uploaded to YouTube:

Read more from iScience Times:

Do Omega-3 Fatty Acids Really Help Your Heart?

Omega-3 Fats Tied to Less Cancer-related Fatigue: Study