Phytoestrogens - Any Clinical Significance?

It is a well recognized fact that there is a high level of non-compliance with women taking Hormone Replacement therapy. Many women are reluctant to take hormones for a number of reasons, mostly relating to the fear of cancer, the dislike of cyclic bleeding, breast tenderness, or the belief that HRT is "unnatural". Nevertheless, the evidence indicates that HRT confers many positive benefits for the post menopausal woman. Recently there has been interest in naturally occurring Phytoestrogens.

Phytoestrogens represent a family of plant compounds that have been shown to have both estrogenic and anti estrogenic properties¹. These compounds fall into two main categories: isoflavones and lignans. Many commonly consumed foods contain appreciable amounts of these different phytoestrogens. Soy and flax products are particularly good sources. In animal studies, and to some extent in humans, these substances have been found to be metabolically active and to have impact on menopausal symptoms as well as other hormone related conditions.

A randomized, double-blind study comparing daily supplements of 45 g soy flour with 45 g wheat flour found a more rapid and continuous reduction of 40% in hot flushes with soy flour compared with wheat flour (25%).

Japanese women, in whom the menopause is often without the hot flushes and other menopausal symptoms experienced by their western sisters, excrete up to 1000 times the amount of isoflavenoid estrogens in their urine.

Biological effects of phytoestrogens (perhaps with only 2% the potency of human estrogens) are likely to be greater in postmenopausal women when estrogen receptors may not be occupied.

Some phytoestrogens have been found to have bone-sparing effects in experimental animals and in some human subjects.

Ingram D², in the Oct 1997 Lancet suggested that there is a substantial reduction in breast-cancer risk among women with a high intake of phytoestrogens. This conclusion was reached after measuring the level of phytoestrogens in the urine of women with breast cancer and in the urine of controls without the disease. This finding generated a number of letters to the editor of the Lancet and these make worthwhile reading. (You will have to register with the Lancet to view these, but registration is free).

There is also evidence that phytoestrogens can slow the progress of cancer of the prostate, at least in rats³.

At present most of the information on phytoestrogens is experimental or epidemiological. More information, and some random double blinded studies will likely appear in the future. In the meantime I'll continue to recommend HRT for my menopausal patients (after the usual history, personal and family, and medical examination), but for those who are not interested, increasing the amount of soy products in the diet offers an option.

- John Hickey

Last updated November 13, 1998