Researchers there found the seaweed effectively reduced levels of estradiol, a hormone associated with breast, endometrial and ovarian cancers, in rats. These rats also experienced a lengthening of their menstrual cycles, another good sign when it comes to preventing breast cancer. Women who have longer cycles have fewer periods over their lifetimes, and fewer periods are linked to a lower risk of the disease.

The study stemmed from an observation made by one of the researchers when treating two women with menstrual problems. After the women began taking kelp supplements, which are available in health food stores, they saw a significant decline in painful symptoms and a lengthening of their menstrual cycles. One of the women also had a drop in blood estradiol levels. “That led me to believe it was worth doing further controlled studies on kelp,” says study author Christine Skibola.

She also decided to study kelp because the food makes up about 10 percent of the Japanese diet, and Japanese women typically have lower breast cancer rates. Scientists have mainly focused on the high level of soy in Japanese diets as an explanation of the lower breast cancer risk, but Skibola speculates kelp may play a role as well.

So, should women run out to their local health food store and stock up on kelp supplements to ward off breast cancer? Not yet, reports the author, noting kelp supplements aren’t for everyone because of high levels of iodine and their tendency to accumulate heavy metals.

Skilbola and her colleagues are currently conducting additional studies to identify the key components in kelp that produce these beneficial effects.

SOURCE: Journal of Nutrition, 2005;135:296-300