Table 1.

Estrogenic potency of phytoestrogens in competitive ER binding assay^a.

Compoundb	Plant	References	IC50 (µM) reported range ER binding
			ERα	ERβ
17β-estradiol (E2)	–	[89, 101, 185]	0.00001 – 0.003	0.0014 – 0.0038
genistein	soy, red clover, kudzu	[50, 101, 185]	0.59 – 1.145	0.025 – 0.09
daidzein	soy, red clover, kudzu	[9, 185, 186]	0.96 – 17	0.1 – 1.20
S-equol	soy, red clover, kudzu	[50, 138, 185]	0.208 – 1.02	0.016 – 0.11
kaempferol	red clover	[80, 186]	8.2	0.05 – 50
puerarin	kudzu	[187]	0.87	NDc
miroestrol	kudzu	[89]	0.0003	NDc
8-prenylnaringenin	hops	[9, 101, 188]	0.057 – 0.51	0.068 – 1.7
liquiritigenin	licorice	[189]	2.80	0.41
glabridin	licorice	[113]	5.00	NDc
glabrene	licorice	[190]	1.00	NDc
lindleyin	rhubarb	[124]	225 – 435	NDc
trans-rhapontigenin	rhubarb	[129]	12	5.6
desoxyrhapontigenin	rhubarb	[129]	26	28
apigenin	chasteberry	[138, 139, 186]	7.88	0.08 – 1.00
penduletin	chasteberry	[139]	NDc	0.31

^aThe values are from different studies and are included for qualitative comparison. Different methods were employed: radiometric binding assay using purified human ER [9, 50, 101, 185], florescence polarization assay using purified human ER [124, 129, 138, 189], radiometric binding assay in cells or tissues [113, 187, 188, 190], inhibition ELISA using purified human ER [186], dextran-coated charcoal method in cells [89].

^bSome compounds might not be plant-specific.

^cND; not determined.