Another sign people are starting to pay closer attention to the healthier eating habits of the Far East: Kelp seaweed, the kind you find walking along the beach, may be emerging as a new cancer-fighting food, specifically to treat breast cancer, according to a new study.

Scientists discovered a diet containing kelp seaweed, a little studied nutrient, lowered levels of the potent sex hormone estradiol in rats, raising hopes it may decrease the risk of estrogen-dependent diseases. The type of kelp used in this study -- bladderwrack seaweed (Fucus vesiculosus) -- is closely related to wakame and kombu, the brown seaweeds most commonly consumed in Japan and the primary form of kelp sold in this country.

Prior studies have shown 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.

Researchers randomly divided 24 female rats into three groups that received either a high (70 milligrams) or low dose (35 milligrams) of dried, powdered kelp for four weeks (roughly equivalent to the amount of brown seaweed eaten by people in Japan) or none at all. After taking daily vaginal swabs to monitor the rats' menstrual cycles, researchers found their estrous cycles increased from an average of 4.3 to 5.4 days for the low dose kelp group, and to 5.9 days for the high dose kelp group.

Overall, dietary kelp resulted in a 37 percent increase in the length of a rat's estrous cycle. Why is that so important? Human studies have linked longer menstrual cycles to a lower risk of breast, ovarian and endometrial cancers. By having fewer periods, researchers say, less time is spent overall in phases where hormone levels and breast and endometrial cell proliferation are at their highest.

Journal of Nutrition 35:296-300, February 2005

Science Blog February 2, 2005