Herbs & Supplements:
Estriol
Supplement Forms / Alternate Names
•
Oestriol, Tri-Estrogen
Principal Proposed Uses
•
Menopausal Symptoms
There are many forms of estrogen in the body. The ovary produces a form named estradiol, which is converted into another important estrogen called estrone. Estriol is yet another form of estrogen metabolized from estradiol, weaker than the other two, but still active.
The estrogen tablets prescribed for menopausal symptoms usually contain estradiol, estrone, or a combination of the two. Some alternative medicine physicians have popularized the use of estriol as an alternative, and there is no doubt that estriol is also effective for symptoms of menopause. However, despite claims that it is safer than other forms of estrogen, the balance of evidence suggests that, in fact, estriol presents precisely the same risks (see Safety Issues below).
Requirements/Sources
Estriol is manufactured in the body from estrone, estradiol, and androstenedione. When taken as a drug, it is manufactured synthetically, or extracted from animal products.
Therapeutic Dosages
The usual dose of estriol is 2 to 8 mg taken once daily. Estriol is also commonly sold in combination with other forms of estrogen.
Therapeutic Uses
Like more common forms of estrogen, estriol is used for the treatment of menopausal symptoms. Double-blind and other controlled trials have found oral or vaginal estriol effective for reducing hot flashes, night sweats, insomnia, osteoporosis, vaginal dryness, and recurrent urinary tract infections.1–9
Estriol may cause less vaginal bleeding as a side effect than other forms of estrogen, although this has not been proven.10,11
Claims that estriol has an anticancer effect are based on exaggerated interpretations of very weak studies.12,13,14 It is more likely that estriol increases cancer risk, just like other forms of estrogen (see Safety Issues, below).
Safety Issues
Like other forms of estrogen, oral estriol stimulates the growth of uterine tissue. This leads to risk of uterine cancer. In a placebo-controlled study of 1,110 women, uterine tissue stimulation was seen among women given estriol orally (1–2 mg daily) as compared to those given placebo.15 Another large study found that oral estriol increased the risk of uterine cancer.16 In another study of 48 women given estriol (1 mg twice daily), uterine tissue stimulation was seen in the majority of cases.17 In contrast, a 12-month double-blind trial of oral estriol (2 mg daily) in 68 Japanese women found no effect on the uterus.18 It may be that the high levels of soy in the Japanese diet altered the results.
For this reason, to protect the uterus estriol, like other forms of estrogen, needs to be balanced with progesterone. Additionally, one study suggests that estriol is less likely to affect the uterus when taken in a once-daily dose rather than in multiple daily doses.19
However, the uterus isn't the only organ at risk of cancer. Test tube studies suggest that estriol is just as likely to cause breast cancer as any other form of estrogen.20 While this doesn't constitute proof, it does raise alarm bells. Until proven otherwise, estriol must be regarded as increasing breast cancer risk.
As with other forms of estrogen, vaginal estriol preparations are safer than oral preparations.21,22
View References
