July 12, 2013
Men with high blood levels of omega-3 fatty acids may have an increase in prostate cancer risk, a new study suggests. Many Americans eat oily fish or take fish oil pills because they contain omega-3s. These fats help fight body inflammation. Fish oil has been widely touted as good for heart health. But more recent research has raised questions about whether it has any effect. The new study suggests that taking omega-3s also could have drawbacks. Researchers used data from a large study that was designed to find out whether selenium or vitamin E could help prevent prostate cancer. (They didn't.) The new study compared blood levels of omega-3 fatty acids in 800 men later diagnosed with prostate cancer and 1,400 who did not develop the disease. Men with the highest levels of omega-3s were 43% more likely to develop prostate cancer than those with the lowest levels. They were 71% more likely to develop aggressive disease. The journal Circulation published the study online. HealthDay News wrote about it July 10.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Confused about fish oil supplements? It's no wonder given all the conflicting information out there.
Here's part of an email sent by a friend:
"OK, I give up. Should I take them? Throw them away? June 29 -- Fish oil may prevent breast cancer. Today (July 11) -- Fish oil may increase risk of prostate cancer."
Fish oil supplements have been promoted as an easy way to:
Such claims are one reason that Americans spend more than $1 billion a year on over-the-counter fish oil. Food companies also are adding it to milk, yogurt, cereal, chocolate, cookies, juice and hundreds of other foods.
What's so special about fish oil? It's loaded with omega-3 fatty acids. Until recently, the general sense has been that the more omega-3s you take in, the more likely you will be to stay healthy.
Omega-3 fatty acids are called essential fats. Our bodies cannot make them. They must be eaten.
Diets that don't provide enough omega-3s can lead to health problems. But getting more than the daily requirement may not translate to better health and disease prevention.
Most research has focused on the positive link between a diet rich in omega-3 fatty acids and heart health. That's the main selling point for fish oil pills.
But newer studies in the last few years have shown that these original assumptions might not be valid for everyone. Several studies showed that fish oil in one form or another didn't work any better than placebo pills at preventing more heart problems among people living with heart disease.
The evidence related to fish oil and cancer has been all over the map. Some research suggests that fish oil pills or diets high in fatty fish might reduce the risk of certain cancers. Other research shows no such link. Now a new study suggests a possible increased cancer risk.
The results of this study were a surprise to the researchers. They compared the risk of aggressive prostate cancer in men with high blood levels of omega-3 fatty acids to men with low levels.
The researchers expected either a cancer protective effect or no effect. But they found that men with higher blood levels of omega-3s had a greater risk of aggressive prostate cancer than those with lower levels.
What Changes Can I Make Now?
Eating lots of fish should still be considered healthy. The amount of evidence supporting this is overwhelming.
The results of this study raise appropriate questions about whether high doses of fish oil might be harmful. But it is only one study. It analyzed data from a study that was not designed to specifically answer those questions. This type of research always has the potential to provide misleading conclusions.
So what should you do if you take fish oil capsules? If your doctor prescribed them, continue to follow your doctor's instructions. For example, high doses of fish oil are an approved and effective treatment for people with high blood triglyceride levels.
If you are taking them on your own because you believe they are good for you, there is not a good answer. If you don't eat any fish, you can get omega-3s through other food sources. Examples include flaxseed oil, English walnuts, canola oil and soy oil. One to two servings per day can help you avoid a deficiency of omega-3s.
Non-fish sources of omega-3s have a reputation of being somewhat inferior to fish sources. So, if you don't eat any fish, it is reasonable to take a fish oil supplement. You shouldn't need more than 500 milligrams of omega-3s per day. And 250 milligrams daily is probably plenty.
But it gets confusing. Most over-the-counter fish oil is sold in 1-gram capsules. So it might seem like you are getting 1 gram of omega-3s. But read the label closely. Usually only about one-third to one-half of the fat content consists of omega-3s. The rest is other types of fat, saturated and unsaturated.
What Can I Expect Looking to the Future?
Experts will surely remain divided on their opinions about fish oil pills for the general population. Don't expect clear advice about what to do any time soon.
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