Flaxseed Might Block Prostate Cancer

Holds Promise as a Cancer Preventive

Nov. 11, 2002 -- There's more positive news about a diet rich in flaxseed. The omega-3 fatty acids and fiber in flaxseed could possibly tame the severity of prostate cancer.

A study of mice shows that flaxseed in the diet helped improve prostate tumors (reducing their size and severity), and even prevented some of the mice from developing the disease.

"We are cautiously optimistic about these findings," says lead study investigator Wendy Demark-Wahnefried, PhD, associate professor of urology at Duke University Medical Center, in a news release. Her study appears in this month's issue of of the medical journal Urology.

Other studies have suggested that dietary fiber reduces cancer risk, and that omega-3 fatty acids have a protective benefit against cancer. Flaxseed is the richest plant source of omega-3 fatty acids and is high in fiber. Flaxseed is also a source of lignan, a specific family of fiber-related compounds that appear to play a role in hormone metabolism.

Since testosterone may be important in the progression of prostate cancer, lignan could help inhibit the growth and development of the disease.

In her study, Demark-Wahnefried used mice that were genetically engineered to develop prostate cancer; the mice were divided into a study group and a control group. The control group ate a normal mouse diet; 5% of the study group's diet was in the form of flaxseed.

Half of the mice in both groups were fed their respective diets for 20 weeks, then tested for tumor growth and spread of the cancer. The rest of the mice were fed the diets for 30 weeks, then their tumors were tested.

"Tumors in the untreated control group were twice the size of tumors in the flaxseed group," reports researcher Xu Lin, MD, PhD, a professor of urology and researcher in the Center for Aging and Human Development at Duke University Medical Center in Durham, N.C.

The tumors were less aggressive in the flaxseed group -- they tended not to grow as fast; two of the mice in the flaxseed group did not develop prostate cancer at all. The flaxseed group also had fewer cases of cancer spreading to other organs, although that finding was not statistically significant, Lin says.

However, Demark-Wahnefried cautions: "The amount of flaxseed given to each mouse was 5% of its total food intake, which would be a very difficult amount for humans to eat, but it does signal that we are on the right track and need to continue research in this area."

This is the Duke group's third study to show the benefits of flaxseed in reducing the growth and development of prostate cancer.

The first, published last year, was a small study showing that men who ate ground flaxseed for 34 days had a drop in levels of testosterone, which helps prostate cancers grow, and in prostate specific antigen (PSA) levels, a marker for prostate cancer.

The second study showed that lignans from flaxseed inhibited the growth of three distinct human prostate cancer cell lines by affecting hormonally driven mechanisms.

Before any conclusions can be made about flaxseed as a cancer preventive, there must be clinical trials, says Demark-Wahnefried. "Our results are encouraging. However, before we can truly state that flaxseed is beneficial in humans, larger well-controlled trials are needed."

An National Cancer Institute-funded clinical trial is currently under way at Duke to test whether a low-fat diet, flaxseed supplements, or a combination of the two is most effective in stopping prostate cancer cells from dividing.