Prostate cancer

22 June 2007

Fish oil may help prostate

A new study with mice suggests that diets high in omega-3 fatty acids from fish might help slow prostate cancer.

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A new study with mice suggests that diets high in omega-3 fatty acids from fish might help slow prostate cancer.

The comparable levels of dietary omega-3s used in the study "are much higher than the average Western diet, but they are not unachievable," said senior researcher Yong Chen, a professor of cancer biology at Wake Forest University School of Medicine in Winston-Salem, North Carolina.

Omega-3 fatty acids - especially the "long-chain" forms found in oily fish - have become the latest nutrition superstars, with studies suggesting they can help prevent heart disease and even cancer.

Mechanism still unclear
The exact mechanism driving the purported anti-cancer effect is still unclear, Chen said. One leading theory contends that specific cellular enzymes metabolise omega-3s in ways that retard malignancy.

However, Chen's team is investigating a much lesser-known mechanism.

"It turns out that [long-chain] omega-3 fatty acids might modulate apoptosis - a form of cell death," he said.

Cancer cells spread in two ways: either they proliferate uncontrollably, or they bypass natural signalling that tells them to commit suicide, or apoptosis.

Helping cells commit suicide
"It turns out that a key molecule - that happens to be called 'Bad' - may be involved in this process," Chen said. His team now believes that long-chain omega-3s interact favourably with Bad to push cancer cells back into a normal apoptosis.

In their study, the researchers fed mice diets high in both omega-3 fatty acid and the less-healthy omega-6 fatty acids. These mice were genetically engineered to lack the Pten tumour suppressor gene, leaving them highly prone to prostate tumours. Dysfunctional Pten plays a key role in about one-third of human prostate cancers, so this mouse is a great model for human disease, Chen said.

As expected, mice with functioning Pten did not develop prostate cancer, the researchers said.

On the other hand, rodents whose Pten was switched off typically developed prostate tumours. However, 60 percent of these mice survived if they were fed a high omega-3 diet, compared to just 10 percent given a low omega-3 diet. None of the mice given the high omega-6 diet survived, the team noted.

There was another wrinkle to the study. In the past, it has been tough for researchers to tease out the effects of omega-6 and omega-3 fatty acids, which usually occur together in foods. But Chen's team introduced another gene into the Pten-less mice. This gene caused the mice to convert omega-6 fatty acids into the omega-3 form, thereby limiting this confounding factor.

"That's really a big strength of this study; nobody had really ever done that before," Chen said.

The study was published on June 21 in the online edition of the Journal of Clinical Investigation.

According to Chen, the study suggests that diets high in long-chain omega-3 fatty acids might give men an edge against prostate cancer.

Not everyone is convinced
"Recent large reviews and meta-analyses tend to suggest no major effects of fish [intake] on cancer risk," said Paul Terry, assistant professor in the department of epidemiology at the Emory University School of Public Health, in Atlanta.

"The fact that they [the Wake Forest researchers] identified and addressed another potential mechanism in their study is certainly helpful," he added. However, he said, "how this mechanism relates to the many others identified and shown in studies to be possibly important remains unclear."

Terry said rodent studies can only tell scientists so much, and "clinical trials in humans of long-chain omega-3 fatty acids and tumour characteristics, for example, are relatively scarce. This study, and others, provides some more rationale for conducting such trials."

Not all omega-3s are equal
For his part, Chen said it's important that consumers realise that not all omega-3s are created equal in terms of their potential health benefits.

"In this study, we are only referring to the long-chain form" found in oily fish, such as mackerel, herring, albacore tuna and salmon, he said. Other, shorter-chain varieties can be found in flaxseed and plant sources, but their impact, if any, on cancer is even less clear.

"We are doing a type of study right now to see whether there is any difference," Chen said. – (HealthDayNews)

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