A new study led by researchers at the University of California, Berkeley, has found that a diet containing kelp seaweed lowered levels of the potent sex hormone estradiol in rats, and raised hopes that it might decrease the risk of estrogen-dependent diseases such as breast cancer in humans.

These new results shine a new light onto the Japanese diet. Prior studies have shown that Japanese women have longer menstrual cycles and lower serum estradiol levels than their Western counterparts, which researchers say may contribute to their lower rates of breast, endometrial and ovarian cancers. Scientists have been searching Asian diets for clues to the lower rates of cancer, with the lion’s share of attention being given to soy.

“Brown kelp seaweed makes up more than 10% of the Japanese diet,” said Christine Skibola, lead author of the study. “Soy has gotten most of the attention, but our study suggests that kelp may also contribute to these reduced cancer rates among Japanese women.”

The researchers say that the type of kelp used in this study, bladderwrack seaweed, is closely related to wakame and kombu, the brown seaweeds that are most commonly consumed in Japan. Bladderwrack seaweed is the primary form of kelp sold in the United States. They say these study results support the need for more research on wakame and kombu.

Skibola said she began the animal study after obtaining encouraging results from earlier case studies of women with highly irregular menstrual cycles.

In a separate test of human ovarian cell cultures, dosing with kelp extract led to a 23 to 35% decrease in estradiol levels.

University of California, Berkeley, Feb 05, 2005