Omega-3 Cancer Risk: Is Fish Oil Linked with Prostate Cancer?

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omega-3 cancer risk
By: Stephen Cummings

We’ve had a number of emails about a recent study showing a link between omega-3s and prostate cancer. This study is concerning since so many people take fish oil supplements. In fact, omega-3s are one of the most popular supplements on the market. That’s because some studies show they lower the risk of heart disease and heart failure, although not dramatically so. They also reduce inflammation.

This study certainly raises some red flags. That’s why we want to cover the topic of omega-3 cancer risk thoroughly and, hopefully, give you some guidance on whether omega-3s are safe.

There’s More Than One Type of Omega-3

As you may know, omega-3s are polyunsaturated fats, fatty acids that have more than one double bond in their structure. They’re found primarily in fatty fish and in fish oil supplements and at lower levels in other sources like grass-fed beef.

What most people don’t realize is there are two types of omega-3s:  short chain and long chain ones. The long chain ones include EPA and DHA. These are the ones found in fatty fish and fish oil supplements.

Long Chain versus Short Chain Omega-3s

Short chain fatty acids are omega-3s you find in plant-based foods like walnuts, sesame seeds and flaxseed. One isn’t necessarily equal to the other in terms of health benefits since they’re structurally different. Short-chain omega-3s can be converted to long-chain omega-3s to some extent once you consume them but the rate of conversion is very low, less than 5%.

More research has focused on the long-chain omega-3s and they’re the ones most people take in supplement form because of their link with cardiovascular benefits. One way long-chain omega-3s may reduce the risk of heart attack is by keeping platelets from clumping together to form a clot.

Long-chain omega-3s also reduce triglycerides, a type of blood lipid linked with heart disease. In addition, they raise HDL, the “good” form of cholesterol that protects against heart disease. Some studies also show they have mood-altering effects that may be beneficial for people with depression. These are all good things – but does it come at a price?

Omega-3s and Prostate Cancer

Based on the fact that omega-3s reduce inflammation, you would expect them to have anti-cancer benefits, not increase the risk for cancer.  Some previous studies HAVE found a link between omega-3s and a reduced risk of some types of cancer – including prostate cancer.

For example, a study published in a leading journal in 2007 involving almost 15,000 men found an association between higher levels of long-chain omega-3s from dietary sources (fish) and a LOWER risk for prostate cancer. There’s also research showing a link between higher levels of omega-3s and a lower risk for colon cancer and breast cancer.

NOW, we have a new study showing an INCREASED risk of prostate cancer in men who have higher levels of omega-3s in their blood. Before jumping to conclusions and throwing out your fish oil capsules, it’s important to differentiate between short chain and long chain fatty acids since they aren’t equal in terms of health benefits. In this study, researchers were measuring levels of long-chain fatty acids from sources like fatty fish, not short-chain omega-3s from plant sources.

More specifically, researchers measured blood levels of long-chain omega-3s among 1,393 healthy men without prostate cancer and 834 men who had prostate cancer. Based on their findings, men with the highest levels of long-chain omega-3s in their blood had a 71% greater risk of developing aggressive prostate cancer and a 44% higher risk of developing any type of prostate cancer compared to those with the lowest levels. Not exactly what most men taking fish oil supplements want to hear.

A Link Between Omega-3s and Prostate Cancer Doesn’t Prove Causation

Keep in mind this doesn’t necessarily show omega-3s CAUSE prostate cancer, only that there’s a link between the two. It’s generally not a good idea to read too much into a single study, especially one that’s simply measuring blood levels of omega-3s in healthy patients versus ones with prostate cancer.

What waves a red flag is the fact that a study in 2008 found a similar link between EPA, a type of long chain omega-3 and prostate cancer. Still another previous study found a link between SHORT CHAIN omega-3s from plant sources and a greater risk for aggressive prostate cancer.

I don’t know about you, but we’re not happy when multiple studies show a similar adverse effect even if you can’t prove causation.

Why Might Omega-3s Be Linked with Prostate Cancer?

One problem with omega-3 fats is they’re polyunsaturated fats, a type of fat that’s unstable and prone towards breaking down into compounds that can damage structures inside cells, potentially leading to DNA damage. When DNA is damaged, it can trigger the growth of a cancer.

Keep in mind this isn’t necessarily the “missing link” between omega-3s and prostate cancer but some experts have raised concerns about this possibility. It IS one potential way omega-3s COULD increase the risk for some types of cancer and one that bears further research.

It’s also possible that a diet rich in fat soluble antioxidants like vitamin E (not supplements) might offer protection against this type of oxidative damage but this is something that needs further study.

Omega-3 Cancer Risk: Should You Take Omega-3 Supplements?

So what should you do? Based on two studies that show a link between long chain omega-3s and prostate cancer, we wouldn’t recommend taking them if you’re a male with a prostate, at least until further research clarifies this issue. What about women? At this point, there doesn’t seem to be data to suggest that omega-3s aren’t safe for women. Whether you’re a man or a woman, it’s a good idea to talk to your doctor about this issue.

Should you get omega-3s from sources like fish? This study didn’t differentiate between omega-3s from fish oil and those from natural sources like fatty fish. Isolated supplements can have vastly different effects when you separate them from a food source – but most of the men in this most recent study weren’t taking a fish oil supplement. That raises questions about whether dietary long-chain omega-3s are also harmful from a prostate cancer standpoint as well. That’s something that will need to be ferreted out through further research.

If omega-3s from fatty fish are such a problem, why don’t areas of the world like Japan that eat lots of it have a higher prostate cancer rate? In fact, they appear to have a lower one. Lots of unanswered questions here.

Should You Exclude Fatty Fish From Your Diet?

Remember, there are benefits to eating fatty fish that go beyond omega-3s. That’s why we don’t recommend completely eliminating fatty fish from your diet unless you’re a male who has prostate cancer or is at high risk for it due to family history. Otherwise, it’s probably safe to eat wild-caught sources of fatty fish twice a week at least until more is known.

Omega-3s do appear to have anti-inflammatory benefits. More specifically, they counteract the effects of too much of another type of dietary fatty acids called omega-6s. They’re fats that are most common in processed and packaged foods and sources like soybean oil, sunflower oil and corn oil. Most people get far too many omega-6s in their diet. This increases their need for omega-3s to help reduce the inflammation that omega-6s create.

One way to reduce inflammation without taking omega-3 supplements is to eliminate processed foods from your diet. Add more whole fruits and vegetables to your diet so you can benefit from their natural anti-inflammatory benefits. Include more anti-inflammatory herbs and spices in your diet like turmeric, ginger, cinnamon and rosemary. There’s more than one way to reduce inflammation. You don’t necessarily need supplemental omega-3s to ease inflammation

Take-Home Points:

  1. More research is needed. These studies don’t prove causation.
  2. It’s probably best to avoid taking omega-3 supplements if you’re male. There’s no evidence at this point to suggest they’re harmful for women.
  3. Fatty fish may or may not be a problem but fatty fish does have other health benefits.
  4. Limit fatty fish to no more than twice a week.
  5. There’s more than one way to reduce inflammation. Eliminate processed foods from your diet and enjoy more anti-inflammatory fruits, vegetables and spices.

Addendum:

We both have taken fish oil supplements for years. Based on this study, Dr. A is stopping them and plans on eating fatty fish twice a week. Dr. K plans on continuing to take them at a dose of 2,000 milligrams a day until more is known.

Hope this clarifies some of the issues about omega-3s and prostate cancer.

References:

Cancer Epidemiol Biomarkers Prev. 2007 Jul;16(7):1364-70.
Memorial Sloan-Kettering Cancer Center. “Omega-3”
National Cancer Institute. “Risk Factors for Prostate Cancer Development”
American Journal of Epidemiology, 2011; 173 (12): 1429 DOI: 10.1093/aje/kwr027.
Journal de l’Association des urologues du Canada 7 (5-6): E333–43.

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Kristie Leong M.D.

Dr. Kristie Leong and Dr. Apollo Leong are physicians helping you to lead a healthy lifestyle by sharing nutrition and fitness tips and keeping you abreast of the latest health news.

6 thoughts to “Omega-3 Cancer Risk: Is Fish Oil Linked with Prostate Cancer?”

  1. Think you both for this info. I am stopping also.
    I am confident you will keep me informed.
    Thanks again,
    Frank

    1. Frank, we’ll stay on it. I’m really curious as to what future studies will show. Thanks for reading. 🙂

  2. Thanks Kristie for this great article. I was really confused after reading about the study to keep taking my fish oil supplement or not. You answered all my questions, and I will resume taking my fish oil once again. Best regards, Karin

    1. Karin, I’m glad you found it helpful. We’ll keep up on the studies and let you know if anything changes. All the best to you. 🙂

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