7 februari 2005: Bron: J Nutr. 2005 Feb;135(2):296-300. en Artikel uit Nutraingredients en BMC Complement Altern Med. 2004 Aug 04;4(1):10

Eetbaar zeewier lijkt voedselcomponent welke wel eens een grote rol zou kunnen spelen in het significant minder voorkomen van hormoonbepaalde kankersoorten als borstkanker en eierstokkanker in Japan en andere Aziatische landen. Dit blijkt uit nog beginnend onderzoek maar veel wijst erop dat eetbaar zeewier door het effect daarvan op de lengte van de menstruatiecyclus en ook het anti-oestrogeen effect hierin naast soja een grote rol zou kunnen spelen. Achtereenvolgens een abstract van meest recente studie bij dieren, een artikel daarover uit Nutraingredients en een eerdere studie waarin drie vrouwen als case stories met effect van zeewier worden beschreven. Elke week een maaltijd met zeewier lijkt, los van de persoonlijke smaak geen kwaad te kunnen dus voor vrouwen met borstkanker of eierstokkanker of ter voorkoming van een recidief of zomaar als preventie.

Brown kelp modulates endocrine hormones in female sprague-dawley rats and in human luteinized granulosa cells.

Skibola CF, Curry JD, Vandevoort C, Conley A, Smith MT. School of Public Health, University of California, Berkeley, California.

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 mumol/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 mumol/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 - in process]

Hier het artikel uit Nutraingredients voer bovenstaande studie:

02/02/2005 - Kelp seaweed, the brown plant often found washed ashore on beaches, could help to fight hormone-related cancers, suggests new animal research.

Researchers at the University of California, Berkeley have found that a diet containing kelp seaweed lowered levels of the most powerful female sex hormone, oestradiol, in rats. Their findings raise hopes that it might decrease the risk of oestrogen-dependent diseases such as breast cancer in humans.

Breast cancer is the most common cancer among women across the European Union. Britain has one of the highest breast cancer death rates in the world, according to Breast Cancer Research, with one woman in nine developing the disease during her lifetime.

"This study opens up a new avenue for research leading to cancer preventive agents," said Martyn Smith, UC Berkeley professor of environmental health sciences and co-author of the study. "Kelp is a little studied nutrient but there's good reason to look at it more closely."

Like soy, the researchers originally became interested in kelp because of its high consumption in Japan and a potential link to the low rates of breast cancer there. Prior studies have shown that Japanese women have longer menstrual cycles and lower serum oestradiol levels than their Western counterparts, which is thought to contribute to their lower rates of breast, endometrial and ovarian cancers.
,br> But scientists searching Asian diets for clues to the lower rates of cancer have mostly focused their attention on soy. The Berkley team say that their new results, published in the February issue of the Journal of Nutrition (135, pp296-300), could demonstrate that soy is not the only dietary component that protects against breast cancer.

"Brown kelp seaweed makes up more than 10 per cent of the Japanese diet," said Christine Skibola, lead author of the study. "Soy has gotten most of the attention, but our study suggests that kelp may also contribute to these reduced cancer rates among Japanese women."

Skibola initially gained encouraging results from supplementing two women with highly irregular menstrual cycles with 700mg of seaweed daily. "It reduced much of the pain associated with endometriosis and significantly lengthened the total number of days of their menstrual cycles," she said.

For the new study, the researchers randomly divided 24 female rats into three groups. One group was fed a high daily dose of 70 milligrams of dried, powdered kelp for four weeks, while a second group was fed a low daily dose of 35 milligrams. Both groups were compared with a third control group of rats that did not receive kelp.
Researchers used bladderwrack seaweed (Fucus vesiculosus), the main form of kelp sold in the US and closely related to wakame and kombu, the brown seaweeds that are most commonly consumed in Japan. The doses given to rats were roughly equivalent to the amount of seaweed eaten by people in Japan.
The researchers report that the rats' menstrual 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 per cent increase in the length of the rat oestrous cycle.
Studies in humans have linked longer menstrual cycle lengths to lower risk of breast, ovarian and endometrial cancers.
"If you have longer cycles, you actually have fewer periods over a lifetime, which means less time is spent overall in the phases where hormone levels and breast and endometrial cell proliferation are at their highest," said Skibola.

During the early part of a woman's menstrual cycle, oestradiol levels remain relatively constant. Almost halfway through the cycle, oestradiol levels surge, peaking just before ovulation. These cyclic periods of high oestrogen stimulate the division of breast cells that already have DNA mutations, as well as increases the chances of developing new mutations, factors that may increase risk of breast cancer.

The study also tested the impact of dietary kelp on oestradiol levels, comparing them before supplementation and after. After just two weeks of eating 35 milligrams a day, oestradiol levels were reduced from an average of 48.9 nanograms per liter to 40.2 nanograms per liter. After four weeks, oestradiol levels dropped further to 36.7 nanograms per liter.

In a separate test of human ovarian cell cultures, dosing with kelp extract led to a 23 to 35 per cent decrease in oestradiol levels. "One possibility is that the kelp may be acting as an oestrogen antagonist by preventing estradiol from binding with its oestrogen 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.

The researchers say they are working to isolate the active compounds in kelp that affect oestradiol levels to avoid the possible toxicity of the high levels of iodine and heavy metals in the plant. "It's a study that points to the need for more studies," said Smith. "But this certainly suggests that there are other elements of the Asian diet beyond soy that should be explored."

Hier een eerdere studie met zeewier gepubliceerd als casestories:

The effect of Fucus vesiculosus, an edible brown seaweed, upon menstrual cycle length and hormonal status in three pre-menopausal women: a case report.

Skibola CF.

School of Public Health, Molecular Epidemiology and Toxicology Laboratory, University of California, Berkeley, CA 94720, USA. chrisfs@berkeley.edu

BACKGROUND: Rates of estrogen-dependent cancers are among the highest in Western countries and lower in the East. These variations may be attributable to differences in dietary exposures such as higher seaweed consumption among Asian populations. The edible brown kelp, Fucus vesiculosus (bladderwrack), as well as other brown kelp species, lower plasma cholesterol levels. Since cholesterol is a precursor to sex hormone biosynthesis, kelp consumption may alter circulating sex hormone levels and menstrual cycling patterns. In particular, dietary kelp may be beneficial to women with or at high risk for estrogen-dependent diseases. To test this, bladderwrack was administered to three pre-menopausal women with abnormal menstrual cycling patterns and/or menstrual-related disease histories.

CASE PRESENTATION: Intake of bladderwrack was associated with significant increases in menstrual cycle lengths, ranging from an increase of 5.5 to 14 days. In addition, hormone measurements ascertained for one woman revealed significant anti-estrogenic and progestagenic effects following kelp administration. Mean baseline 17beta-estradiol levels were reduced from 626 +/- 91 to 164 +/- 30 pg/ml (P = 0.04) following 700 mg/d, which decreased further to 92.5.0 +/- 3.5pg/ml (P = 0.03) with the 1.4 g/d dose. Mean baseline progesterone levels rose from 0.58 +/- 0.14 to 8.4 +/- 2.6 ng/ml with the 700 mg/d dose (P = 0.1), which increased further to 16.8 +/- 0.7 ng/ml with the 1.4 g/d dose (P = 0.002).

CONCLUSIONS: These pilot data suggest that dietary bladderwrack may prolong the length of the menstrual cycle and exert anti-estrogenic effects in pre-menopausal women. Further, these studies also suggest that seaweed may be another important dietary component apart from soy that is responsible for the reduced risk of estrogen-related cancers observed in Japanese populations. However, these studies will need to be performed in well-controlled clinical trials to confirm these preliminary findings. PMID: 15294021 [PubMed - indexed for MEDLINE]

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