Flaxseed and prostate cancer

Secret in the Seed

The dangers of prostate cancer are widely reported. And for most HSI members, the benefits of omega-3 fatty acids are well known. Now a new study from the National Cancer Institute (NCI) shows that prostate cancer prevention may be one of the most important items on the list of omega-3 benefits. But it was another detail in this study that really caught my attention: the confirmation that a nutrient that’s beneficial for most of us may actually increase the risk of pushing prostate cancer to an advanced stage.

Omega-3s to the rescue

In the July issue of the American Journal of Clinical Nutrition, NCI researchers report on their examination of dietary and medical records of more than 47,800 men, aged 40 to 75, with no cases of cancer diagnosed at the outset.

After following the subjects for 14 years, 2,965 of the subjects had developed prostate cancer, and more than 440 of these cases were advanced. The NCI team analyzed the dietary data, giving particular emphasis to intakes of EPA and DHA omega-3 fatty acids, and alpha-linolenic acid (ALA), a precursor of omega-3 fatty acids. The results:

* Dietary intake of EPA and DHA was associated with lower risk of prostate cancer.

* The highest intake of combined EPA and DHA was associated with more than 10 percent lower overall prostate cancer risk, compared to the lowest intake of EPA and DHA.

* Advanced prostate cancer risk was more than 25 percent lower among those with the highest EPA and DHA intake.

The ALA results were mixed. Among men who reported only moderate intake of ALA, there was no association with a risk of prostate cancer overall. But for the men who developed prostate cancer and also had the highest level of ALA intake, the risk of their cancer developing to an advanced stage was sharply increased.

The highest intake of non-animal sources of ALA was associated with twice the risk of advanced prostate cancer, compared to the highest intake of animal sources of ALA.

Beneficial seed

In several e-Alerts I’ve told you about the importance of eating plenty of foods rich in omega-3 fatty acids, found primarily in fish (such as salmon and mackerel), flaxseed, walnuts, wheat germ, and fish oil.

Good sources of alpha-linolenic acid include flaxseed, walnuts, dark green leafy vegetables, and meat, as well as oils such as flaxseed, linseed, rapeseed, and mustard oil. Research has shown that ALA may help promote blood vessel resiliency, while slowing and perhaps even preventing the growth of breast and colon cancer. So while most ALA foods provide excellent nutrition, one ALA source in particular should be avoided by men who are at risk of prostate cancer: flaxseed oil.

Flaxseed contains lignans, a fiber and phytoestrogen with a chemical makeup similar to human estrogen. And because lignans are believed to help remove testosterone from the body, they may assist in suppressing the growth of prostate cancer cells. But the lignans in flaxseed are concentrated in the outer shell of the seeds. So when the seeds are refined into oil, only a trace of the lignans ends up in the finished product. This process dramatically increases the concentration of ALA.

Flaxseed and flaxseed oil both have a very high omega-3 content and an excellent balance of omega-3 to omega-6. A tablespoon of flaxseed oil contains approximately 8 grams of omega-3 fatty acids, but only 2.2 grams of omega-6. No other oil comes close to this beneficial balance.

So bottom line: Most men will not have problems with normal ALA intake; in fact, it will do them good. But for those with an elevated risk of prostate cancer, large quantities of ALA foods (especially flaxseed oil) should be avoided.

The E team

No discussion of prostate cancer prevention would be complete without a mention of two key nutrients: vitamin E and selenium.

In the e-Alert “Taking Yourself Off the List” (4/22/04), I told you about a trial of 300 middle-aged men in Finland. Those who took a vitamin E supplement for more than five years reduced their prostate cancer risk by almost a third, compared to men who didn’t supplement with the vitamin. And risk dropped even further for those who also ate foods rich in vitamin E (including almonds, spinach, mustard greens, green and red peppers and sunflower seeds).

And in the e-Alert “Trace Mineral Key to Preventing Prostate Cancer” (12/5/01), a Stanford University study demonstrated that men with low blood levels of selenium may be four to five times more likely to develop prostate cancer than men with normal levels of the mineral. The study also confirmed that selenium levels decrease as men age – mirroring the fact that prostate risk steadily rises as men age.

Besides the fact that selenium has excellent antioxidant properties that have been shown to help increase insulin efficiency, selenium also enhances the effect of vitamin E, making it a perfect match for any vitamin E regimen designed to help prevent prostate cancer. Foods that contain selenium include fruits and vegetables (if grown in selenium-rich soil), beef, tuna, turkey, chicken, eggs and whole wheat bread. Brazil nuts contain more selenium than any other food: 840 mcg of selenium per ounce.


“Dietary Intake of N-3 and N-6 fatty Acids and the Risk of Prostate Cancer” American Journal of Clinical Nutrition, Vol. 80, No. 1, July 2004, ncbi.nlm.nih.gov
“Omega-3s Appear to Protect Against Prostate Cancer” NutraIngredients.com, 6/23/04, nutraingredients.com
“Higher Serum Alpha-Tocopherol and Gamma-Tocopherol Concentrations are Associated with Lower Prostate Cancer Risk” American Association for Cancer Research, 95th Annual Meeting, Abstract No. 1096, 3/28/04, aacr.org