During the early part of a woman's menstrual cycle, estradiol levels remain relatively constant. Almost halfway through the cycle, estradiol levels surge, peaking just before ovulation. These cyclic periods of high estrogen, which continues over a span of about 40 years from puberty to menopause, stimulates the division of breast cells that already have DNA mutations, as well as increases the chances of developing new mutations, factors that may increase one's risk of breast cancer.
To test the impact of dietary kelp on estradiol levels, researchers took baseline blood samples from 19 rats immediately before their low dose diet of kelp began. After just two weeks of eating 35 milligrams a day, estradiol levels were reduced from an average of 48.9 nanograms per liter to 40.2 nanograms per liter. After four weeks, estradiol levels dropped further to 36.7 nanograms per liter.
In a separate test of human ovarian cell cultures, conducted in collaboration with colleagues at UC Davis, dosing with kelp extract led to a 23 to 35 percent decrease in estradiol levels.
"One possibility is that the kelp may be acting as an estrogen antagonist by preventing estradiol from binding with its estrogen receptors," said Skibola. "Our next step is to try to isolate the active compound in kelp that is having this hormone-modulating effect."
She noted that seaweed contains several complex compounds, including polyphenols that are considered antioxidants. Kelp supplements are available in health food stores since they are taken as a source of iodine by people with thyroid conditions. However, the researchers caution against a run on kelp because of these early results, particularly be
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Contact: Sarah Yang
scyang@berkeley.edu
510-643-7741
University of California - Berkeley
2-Feb-2005