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Luteolin, the anti-oestrogen in celery
Luteolin, a flavonoid that we consume daily through our food, inhibits the body's production of estradiol. Researchers at the Chengdu Institute of Biology in China report their findings in the Journal of Agricultural and Food Chemistry. In their test tubes luteolin reduces the production of the enzyme aromatase by cells.
Less estradiol, please
There are effective pharmacological estradiol inhibitors, but they have side effects. That's why researchers are looking for naturally occurring substances that inhibit the enzymes that convert androstenedione and testosterone into estradiol, which would mean that the dose of pharmacological anti-oestrogens could be reduced.
Luteolin is a flavonoid that we consume daily via foods such as celery, green paprika and peppers, onions, parsley, cabbage and apple peel.
In 1994 scientists at the University of Minnesota published the results of an in-vitro study which showed that luteolin sabotaged the synthesis of aromatase in young fat cells. [J Steroid Biochem Mol Biol. 1994 Aug;50(3-4):205-12.] In 2011 biochemists at the Chinese University of Hong Kong discovered that luteolin had the same effect in MCF-7 breast cancer cells. [Mol Cell Endocrinol. 2011 Sep 15;344(1-2):51-8.]
The Chinese exposed their KGN cells to 10 micromols luteolin, 10 micromols forskolin [a cAMP booster that therefore boosts aromatase synthesis and/or 50 micromols formestan [an anti-oestrogen that sabotages the effect of aromatase]. And lo and behold. Luteolin works better than formestan.
The researchers discovered that luteolin doesn't actually do anything to the aromatase enzyme itself: luteolin inhibits the synthesis of aromatase.
The Chinese suspect that luteolin is a cAMP inhibitor. They base their reasoning on a Korean in-vitro study from 2008. [Arch Pharm Res. 2008 Sep;31(9):1166-71.]
Luteolin bears a remarkable resemblance to isorhamnetin, kaempferol, quercetin and myricetin. So the Chinese also measured the extent to which these flavonoids were capable of inhibiting estradiol synthesis in their KGN cells.
Luteolin was the best estradiol inhibitor. It inhibits estradiol synthesis at a concentration as low as 1 micromole. In second place was kaempferol.
This dose – human equivalent 3 mg per kg – is probably safe. According to an animal study performed at the Yong Loo Lin School of Medicine in School, rats can be given 30 mg luteolin per kg bodyweight daily without showing signs of toxicity. [Chem Biol Interact. 2006 Dec 1;164(1-2):1-14.]