Prostate cancer: The flaxseed paradox

Flax has been used cultivated and used for centuries and any traditions are associated with this useful plant. In the Middle Ages flax flowers were believed to be a protection against sorcery and the Bohemians have a belief that if seven-year-old children dance among flax, they will become beautiful. The seeds as well as the woven cloth from flax have even been found in Egyptian tombs.

Flaxseed which is also known as linseed has numerous health benefits so lets take a look at how we use it in modern medicine today.

Why choose flaxseed?
Earlier this year I sent you an e-alert 'Improve your well being with a daily dose of flaxseed oil' (17/5/05) that examined the dietary importance of maintaining a proper balance of the two groups of essential fatty acids: omega-6 and omega-3. Nutritionists generally agree that the optimal balance of these two should be 1:1, or at least close to that.

Most diets, however, are high in omega-6 (readily available in the oils used in many processed foods) and low in omega-3. The most common dietary source of omega-3 is fish, especially dark-meat fish like swordfish and tuna. To avoid mercury, a high quality fish oil supplement is a good source as well. And here is where flax makes its appearance.

Flaxseed contains lignans, a fibre and phyto-oestrogen with a chemical makeup similar to human oestrogen. Lignans are also a good source of alpha-linolenic acid, which is converted by the body into omega-3 fatty acids, which improve cell function in the lining of the heart and blood vessels, lower triglyceride levels, and inhibit platelet clumping. And because lignans are believed to help remove testosterone from the body, they may assist in suppressing the growth of prostate cancer cells.

Show me the lignans
'Lignans are thought to be the active agents responsible for stopping growth of prostate cancers in the Duke University study of 2001.'

This comment came from an HSI member named Rick. And he's right - the Duke University (US) research did show strong indications that flaxseed may be effective against prostate cancer - especially in the development of the cancer in the early stages. But the study was relatively small (only 25 men), and brief (only 34 days). And while the positive effect on several markers associated with prostate cancer was described as significant, the study was designed to examine the combined effects of flaxseed and a low-fat diet.

In other words: we have yet to see a sizeable study of extended length that judges whole flaxseed alone. So while we don't yet have overwhelming evidence that it helps prevent prostate cancer, there are promising signs that this evidence is emerging. Meanwhile, we have to acknowledge the ironic prospect that flaxseed OIL (not flaxseeds, but the oil) may in fact promote the spread of prostate cancer cells.

Dissecting the paradox
The valuable lignans in flaxseed are found in the outer shell of the seeds. But when the seeds are refined into oil, only a trace of the lignans ends up in the finished product. This same process dramatically increases the concentration of alpha-linolenic acid (ALA), one of the primary omega-3 fatty acids. And while some studies have suggested that ALA may slow cancerous growth in the breast and colon, the effect on prostate cancer is an entirely different story.

Out of six known studies that have examined the association between the risk of prostate cancer and the intake of dietary alpha-linolenic acid, five of them found the cancer risk to increase with greater intake of ALA. And one of these studies - a trial from the Registro Nacional de Cancer, Montevideo, Uruguay - concluded that the two major risk factors associated with prostate cancer are a family history of prostate cancer and intake of alpha-linolenic acid.

Do you ingest ALA when you eat flaxseeds? Yes, but compared to the ALA content of flaxseed oil, the ALA in the seeds is generally considered too low to be harmful to prostate cancer patients.

The jury is still out on the effects of flaxseed and flaxseed oil on prostate cancer. But further studies are now in the works, and as they're reported, the grey areas in this field of study will come into clearer focus.