Blueberries have an antioestrogenic effect
The phenols in blueberries make cells less sensitive to the detrimental effects of estradiol, but leave the desirable effects of the hormone intact. It's possible to draw this conclusion from an animal study done by oncologists at the University of Louisville in the US, which have been published in the Journal of Agricultural and Food Chemistry.
Blueberies, anthocyanins & cancer
Fruit contains anthocyanins, and cell- and animal studies have shown that these offer protection against breast cancer. Chemists have classified the approximately five hundred known anthocyanins into six groups: cyanidin, delphinidin, malvidin, pelargonidin, peonidin and petunidin. Blueberries contain all the groups except pelargonidin.
For this reason - and perhaps also because the Californian Highbush Blueberry Council was prepared to fund the study - the Louisville researchers examined the effects of blueberries on the emergence and development of breast cancer.
In the article that has been published in the Journal of Agricultural and Food Chemistry the researchers describe experiments they did on female ACI rats. These are rats that are susceptible to cancer. The researchers gave the majority of the rats implants that secreted estradiol [E2], thus increasing the chance that the animals would develop breast cancer.
The lab rats in the experimental groups were given food that consisted for 2.5 or 5 percent of freeze-dried powdered blueberries [BB]. Some of the rats were given this enriched food two weeks before being fitted with the estradiol implant [Preventive]; others were given it 14 weeks after the first tumours had been detected [Therapeutic].
The figure below left shows that the extracts prevented tumour development in up to forty percent of the rats. In addition - as the figure below right shows - the extracts inhibited the growth of the tumours.
The figures above show how the extract works. To start with blueberries inhibit the synthesis of the enzyme CYP1A1 in the breast cancer cells. This enzyme converts estradiol into 2-hydroxy-estradiol. Hydroxylated estradiol analogues can cause DNA damage. The researchers interpret that as a positive sign. (We are less enthusiastic about this. The 2-hydroxyl estradiol analogue is not so risky.)
The figure on the right above is more interesting. Blueberries inhibit the synthesis of the alpha-estradiol receptor. Via this receptor estradiol stimulates breast development, fat deposition and moisture retention – but also tumour growth. The beta-estradiol receptor is particularly important for many of the positive effects of estradiol, such as supple blood vessels and strong bones.
The human equivalent of the highest dose in the experiment is about 30 g blueberry powder daily. However, the powder was not a concentrate and only contained 38 mg phenols (of which 21 mg anthocyanins) per gram. If you're thinking of using blueberries as an antioestrogenic supplement, and you can find a good quality extract, a few capsules per day will probably be enough.
"Thus, the consumption of blueberries can be used as an effective strategy for treatment of estradiol-associated breast cancer and possible prevention of its relapse and metastasis", the researchers write.
"Thus, our study demonstrates the chemopreventive and therapeutic potential of blueberry and advances our understanding into the working mechanisms in search of potential future drugs."
J Agric Food Chem. 2014 May 7;62(18):3963-71.
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