A study published July 11 in the online edition of the Journal of the National Cancer Institute suggests that men who have high intakes of Omega-3s are at increased risk of developing prostate cancer.
If you regularly take an Omega-3 supplement, this news may be somewhat confusing. Below we review the study findings then provide dietary and lifestyle recommendations on how you can reduce your risk of developing prostate cancer.
The SELECT Study
In the current study, scientists at the Fred Hutchinson Cancer Research Center in Seattle used data and samples collected from the Selenium and Vitamin E Cancer Prevention Trial or SELECT. This study tested whether selenium and vitamin E, alone or in combination reduced prostate cancer risk.
Researchers used data obtained from a sample of men enrolled in SELECT. More than 800 men over the age of 55 later diagnosed with prostate cancer were used for the analysis. Nearly 1,400 men not diagnosed with prostate cancer were used for comparison.
Fatty acids were analyzed from a single blood serum sample taken at the start of the SELECT study. The level of Omega-3s (EPA, DHA, DPA) and other fats (Omega-6 fats, trans-fats) were measured in the blood as a percentage of total fatty acids. For each fat, the results were placed into one of four groups or quartiles.
Using statistical modeling, scientists then compared the blood level concentrations of Omega-3 fatty acids in men who had been diagnosed with cancer with men who had not.
What they found is that Omega-3s were associated with a 43% increased risk for prostate cancer overall and a 71% increased risk in aggressive prostate cancer.
The lowest risk group for developing prostate cancer had a 3.2% blood level concentration of Omega-3 fatty acids, compared to 5.7% in the high risk group. Although information about diet was not obtained, this 2.5% gap is larger than achieved by eating salmon twice week.
Why Would Fish Oil Promote Prostate Cancer?
It remains unclear why high concentrations of Omega-3 fatty acids are associated with a heightened risk of prostate cancer.
“That’s the million dollar question,” said lead author Theodore Brasky, a research assistant professor at Ohio State University Comprehensive Cancer Center in Columbus.
He speculated that perhaps in high doses, fish oil could cause oxidative stress which can lead to DNA damage and possibly increase the risk for prostate cancer.
Omega-3s are anti-inflammatory which means that in general they subdue immune system responses. This is likely protective against chronic inflammation, allergy and autoimmune disease. David L. Katz, M.D., Director, Yale Prevention Research Center hypothesized that “an attenuation of that immune system vigilance in the form of an anti-inflammatory effect, could, conceivably help give cancer the upper hand.”
Stop Eating Fish? Stop Taking Fish Oil Supplements?
Before you stop eating salmon or discontinue taking your fish oil supplement, it’s worth taking a closer look at the study design.
This study just showed that Omega-3 fatty acids are associated with increased prostate cancer risk; it was not designed to look at the exact relationship between Omega-3 fatty acid intake and prostate cancer. The study results may have been confounded with selenium and vitamin E used in the original SELECT treatment groups.
If the findings were true, then prostate cancer would be rampant in countries that have high seafood consumption (e.g., Scandinavia, Japan) but this is not the case.
The average Omega-3 content was 4.66% in the cancer group versus 4.48% in the control. It is questionable that just a 0.2% difference would make a difference in cancer outcome.
Blood plasma levels of fatty acids is not a good index of long term intake and are influenced dramatically by a single meal, or even timing of a fish oil dose. For example, a single fish oil dose dramatically increases Omega-3 levels in about 4-12 hours then washes out around 48 hours.
The type of statistical model used (Cox proportional hazards) was not appropriate for the study. This model is suitable for a drug taken at the same time every day but not for fish or fish oil intake where levels in the blood vary considerably depending on food and supplement consumption patterns.
Inflammation plays a role in the development of many cancers. Given that Omega-3 fats have anti-inflammatory actions in the body, it seems counterintuitive that higher intake of these health-promoting fats would promote the development of cancer. Conversely, trans-fats and Omega-6 fats have pro-inflammatory actions in the body yet in this study, higher intake of these fats was associated with lower risk of developing prostate cancer.
The study only measured Omega-3 blood levels in men but did not include information on the participants’ eating habits. Researchers could not differentiate between the effects of fatty acids from fish or those from supplements. However, the overwhelming majority of participants did not take fish oil supplements.
In this study, men diagnosed with cancer at baseline were more educated, had a higher PSA (prostate-specific antigen score) and a larger proportion of first-degree relatives with a history of prostate cancer. If any of these risk factors caused these men to increase their Omega-3 intake as a protective measure, the study could be evidence of causality.
What Do Other Prostate Cancer Studies Say?
The conclusions drawn from this study is in stark contrast to other epidemiologic studies. Previous studies not only demonstrate no correlation between Omega-3 consumption through fish and/or supplementation and the risk of prostate cancer but in many cases showed a protective effect.
A recent meta-analysis of fish consumption and prostate cancer reported a 63% reduction in late stage or fatal prostate cancer among study participants.
In the Physician’s Health Study, over 20,000 men were studied over a period of 22 years. Researchers found that of the men diagnosed with prostate cancer, the men who ate fish at least 5 times a week had a 48% lower risk of dying from prostate cancer.
Risk Factors for Prostate Cancer
Prostate cancer is really several diseases with different causes. The more aggressive form has different underlying causes than slower growing tumors. And, it is the aggressive form the carries the highest risk of serious health problems.
A criticism of the current study is that it didn’t account for other risk factors which include age, race, family history, Body Mass Index (BMI), among other things.
Age. Prostate cancer is the most common cancer in men and like breast cancer; age is a risk factor for developing the disease. If most men live long enough, they will develop prostate cancer. More than 65% of all prostate cancers are diagnosed in men over the age of 65.
Race. African American men are more likely to develop prostate cancer compared with Caucasian men and are 2.5 times as likely to die from the disease.
Family History/Genetics. A man with a father or brother who developed prostate cancer is twice as likely to develop the disease.
Body Mass Index. BMI is not linked to being diagnosed with prostate cancer but obese men are more likely to have aggressive prostate cancer.
Excess Abdominal Fat. Excess fat, especially around the middle of the body, has been associated with an increased risk of many diseases including prostate cancer, particularly aggressive prostate cancer. Body fat secretes hormones and specialized proteins that can increase inflammation and oxidation in the cells of the body – both which can contribute to development and progression of prostate cancer.
Smoking. While smoking is not thought to be a risk factor for low-risk prostate cancer, it may be a risk for aggressive prostate cancer.
Where You Live. Men who live in cities north of 40 degrees latitude (north of Philadelphia, Columbus, OH and Provo, UT) have the highest risk for dying from prostate cancer of any men in the U.S. This effect appears to be mediated by inadequate sunlight during the winter months, which reduces vitamin D levels.
Prevention of Prostate Cancer
Studies have shown that lifestyle – especially nutrition and exercise – has a significant influence in prostate cancer prevention and treatment. Not surprisingly, the dietary and lifestyle recommendations that prevent cancer development also protect you from becoming overweight, developing cardiovascular disease and type 2 diabetes.
- Eat fewer calories to maintain a normal body weight. Excess weight has been associated with more severe and rapidly progressive prostate cancer.
- Eat more colored fruits & vegetables. These foods contain phytonutrients that are associated with many health benefits especially anti-inflammatory.
- Avoid overcooking any type of meat at high temperatures. Charred meat produces a set of carcinogens that are known to trigger mutations in prostate cell DNA, leading to a chronic inflammatory response.
- Increase your intake of cruciferous vegetables. Broccoli, cauliflower, Brussels sprouts have unique properties that allow them to sponge up carcinogens.
- Reduce your consumption of simple carbohydrates. Sugar is a primary energy source for many cancers. Excess sugar intake is linked to prostate cancer growth through its interactions with insulin.
- Talk with your doctor. Together you can discuss your family and health history to determine the appropriate time to get PSA screenings.
- Avoid smoking. While it’s hard to avoid all exposure to carcinogens, you can avoid increasing your exposure to carcinogens that contribute to development of prostate cancer.
For more information, refer to the Prostate Cancer Foundation’s Nutrition & Exercise Guide.
The Bottom Line
This study, like so many, has generated more questions than it has answered. Even so, most experts don’t encourage men to change their diet but to speak with their doctor if they have concerns about prostate cancer.
Based on our review of this study and others that have looked at prostate cancer, we also do not recommend that you stop eating fatty fish or discontinue taking your fish oil supplements. At the same time, we recommend that you not megadose on anything – whether it be foods or nutritional supplements – as too much of a good thing may have unintended consequences. So, if you enjoy salmon or another fatty fish once or twice a week, then continue doing so. This is especially true if you’ve replaced red meat with fish.
Based on the well-documented benefits of consuming Omega-3s for brain, eye and heart health throughout life, we continue to recommend that Americans of all ages augment their diet with 1 to 2 capsules of a high-quality fish oil like our Super EPA/DHA Fish Oil supplement especially if they’re not getting sufficient Omega-3s from diet alone.