Kelp, or bladderwrack seaweed – scientific name Fucus vesiculosus – has an anti-estrogenic effect. Substances found in kelp delay the manufacture of estradiol in the body and sabotage the working of the estradiol receptor.
Researchers at the University of California at Berkeley stumbled upon the anti-estrogenic effect of kelp when they tested an alternative theory on why very few Japanese women have breast, womb or ovarian cancer. These types of cancer are caused by estradiol. The conventional theory is that high consumption of soya, a food with an anti-estrogenic effect, protects Japanese women against estradiol-related cancers.
The researchers, however, had a different theory. The Japanese eat between 3 and 13 g of seaweed every day. That led the Americans to wonder whether seaweed also has anti-estrogenic effect. They did a simple experiment in which female rats received 175 or 350 mg of seaweed per kg of bodyweight each day. The highest dose was the most effective and reduced the concentration of estradiol in the rats by almost 40 percent. The graph below shows this.
Because the researchers wanted to understand the mechanism by which kelp reduces estradiol levels, they exposed human ovary cells – technically speaking luteinized granulosa cells – to different concentrations of kelp. The cells produce small amounts of testosterone, estradiol and progesterone. The higher the concentration of kelp, the less estradiol the cells made, the Americans discovered. The production of progesterone rose slightly.
The researchers wanted to know more about how the process works so they did another experiment. In test tubes they tested whether certain substances in kelp were capable of sabotaging the receptors for estradiol and progesterone. And yes, they managed to do so, see here below.
Kelp contains many polyphenols and sulfated sugar chains, fucoidans. Exactly which of the components is responsible for the anti-estrogen effect the researchers do not know.
Supplements that also have an anti-estrogen effect are Ginkgo biloba, green tea and gamma-linoleic acid. According to researchers at the US Department of Agriculture, mushrooms also have an anti-estrogenic effect.
Brown kelp modulates endocrine hormones in female sprague-dawley rats and in human luteinized granulosa cells.
Epidemiological studies suggest that populations consuming typical Asian diets have a lower incidence of hormone-dependent cancers than populations consuming Western diets. These dietary differences have been mainly attributed to higher soy intakes among Asians. However, studies from our laboratory suggest that the anti-estrogenic effects of dietary kelp also may contribute to these reduced cancer rates. As a follow-up to previous findings of endocrine modulation related to kelp ingestion in a pilot study of premenopausal women, we investigated the endocrine modulating effects of kelp (Fucus vesiculosus) in female rats and human luteinized granulosa cells (hLGC). Kelp administration lengthened the rat estrous cycle from 4.3 +/- 0.96 to 5.4 +/- 1.7 d at 175 mg . kg(-1) body wt . d(-1) (P = 0.05) and to 5.9 +/- 1.9 d at 350 mg . kg(-1) . d(-1) (P = 0.002) and also led to a 100% increase in the length of diestrus (P = 0.02). Following 175 mg . kg(-1) . d(-1) treatment for 2 wk, serum 17beta-estradiol levels were reduced from 48.9 +/- 4.5 to 40.2 +/- 3.2 ng/L (P = 0.13). After 4 wk, 17beta-estradiol levels were reduced to 36.7 +/- 2.2 ng/L (P = 0.02). In hLGC, 25, 50, and 75 micromol/L treatment reduced 17beta-estradiol levels from 4732 +/- 591 to 3632 +/- 758, 3313 +/- 373, and 3060 +/- 538 ng/L, respectively. Kelp treatment also led to modest elevations in hLGC culture progesterone levels. Kelp extract inhibited the binding of estradiol to estrogen receptor alpha and beta and that of progesterone to the progesterone receptor, with IC(50) values of 42.4, 31.8, and 40.7 micromol/L, respectively. These data show endocrine modulating effects of kelp at relevant doses and suggest that dietary kelp may contribute to the lower incidence of hormone-dependent cancers among the Japanese.
PMID: 15671230 [PubMed – indexed for MEDLINE]