THURSDAY, Feb. 3, 2005 (HealthDay News) -- More than just a slimy nuisance that wraps itself around your ankles while you walk the beach, seaweed may actually be a powerful tool in the fight against breast cancer.
That's because a diet containing kelp seaweed may reduce the amounts of estrogen circulating in the body, a new study claims. Lower estrogen levels mean there's less fuel available for the development of estrogen-dependent cancers, such as some forms of breast cancer, the researchers explain.
This study, which appears in the Feb. 2 issue of the Journal of Nutrition is the latest to examine differences between the typical Asian diet and the typical Western diet, looking at how those differences might contribute to the development of breast cancer.
Japanese women, who have a significantly lower risk of breast cancer than women in the United States, also have a much higher dietary intake of seaweed, according to the study.
In Japan, seaweed is used in the preparation of sushi dishes, in Miso soup, in stews, and as a thickening agent. In some Asian countries, seaweed is even eaten as a snack, said study author Christine Skibola, an assistant research toxicologist at the University of California at Berkeley School of Public Health.
The current study, done in rats, developed out of several case studies Skibola had conducted on women taking 700-milligram seaweed supplements daily to treat extremely irregular menstrual cycles from disorders such as endometriosis. Skibola noticed the women's menstrual cycles became longer and more regular, and that their blood levels of estradiol -- a form of estrogen -- dropped significantly.
"It was kind of amazing how much it helped their pain and how it altered their menstrual cycles, and we saw a remarkable decrease in estradiol levels," said Skibola, who stressed that while these case studies were remarkable, they were conducted in just three women.
To further test the effects of seaweed, Skibola and her colleagues had rats consume bladderwrack seaweed, which is closely related to two Japanese favorites, wakame and kombu seaweed.
The study included 24 female rats, split into three different groups. One group was given a high dose -- 70 milligrams -- of kelp, while another group was given 35 milligrams daily. These doses are about equivalent to the normal Japanese diet, said Skibola.
The third group served as a control group and was given no kelp. To ensure that the rats consumed the correct dose of dried kelp, it was sprinkled onto their favorite food, apples.
After four weeks, the researchers found that consumption of kelp increased the average length of the rodent's menstrual cycle by 37 percent. At the start of the study, the average menstrual cycle was 4.3 days. After consuming kelp, the low-dose group averaged 5.4 days, and the high-dose group increased to 5.9 days.
When the researchers tested blood levels of estradiol in rats from the low-dose kelp group they found declines in the hormone from 48.9 nanograms per liter at the start of the study to 36.7 nanograms per liter four weeks later.
According to Skibola, the researchers also tested human ovarian cells in culture and found that the cells' estrogen levels fell when exposed to kelp extract.
Skibola explained that compounds in seaweed appear to compete with estrogen for for spots on estrogen receptors in cells. The overall effect could be reductions in circulating estrogen.
By increasing the length of the menstrual cycle and decreasing levels of estrogen, the researchers suggest that seaweed could reduce the risk of estrogen-dependent breast cancers because there would simply be less estrogen available to fuel tumor growth.
Others aren't convinced, however.
"I think this is interesting, but it's another theory," said Dr. David Decker, chief of hematology and oncology at William Beaumont Hospital in Royal Oak, Mich. "They've shown that seaweed given to rats can change their estrogen levels, but we don't know for sure if that applies to humans."
"Women shouldn't go out and start eating lots of seaweed," said Decker, who added that it's probably more important for breast cancer prevention to eat an overall healthy diet and to make sure you get screening mammograms beginning in your 40s.
Skibola also hopes that no one consumes large quantities of seaweed, but says that in moderation it can be a healthy addition to the diet. But, she cautioned, seaweed does contain iodine and low levels of some heavy metals, so large amounts, whether in dietary or supplement form, may not be good for some people.
"I don't think people should go out and self-medicate, but in the diet, seaweed is generally a healthy thing to incorporate," she said.
Skibola said that the researchers are trying to isolate exactly which compounds in seaweed effect estrogen levels, in hopes that they may one day be able to develop a drug from those compounds to help prevent estrogen-dependent cancers.
To learn more about preventing breast cancer, visit the National Cancer Institute.