Can Isoflavone Supplements Reduce Your Breast Cancer Risk?

A Canadian study has found that if you take supplements that contain isoflavones, such as soy, red clover, garlic and evening primrose, for a period of at least five years, you have a 25% lower risk of developing cancer. However, the researchers from the University of Toronto only saw these results in post-menopausal women.

According to the study’s authors, who published their findings in the International Journal of Cancer, ‘Our findings suggest isoflavone supplements are associated with reduced post-menopausal breast cancer risk. Furthermore, it appears that isoflavone supplements do not increase breast cancer risk and may represent a possible modifiable approach to reduce risk.’

So far, the evidence for isoflavones’ role in breast cancer prevention has been conflicting. This is because soy isoflavones are well-known phytoestrogens – plant-derived active substances that act weakly like oestrogen. Some study results have even implied that isoflavones stimulated breast cancer in mice, whereas population studies have shown lower rates of breast cancer in women with a high-soy diet.

Data of 3,101 women with breast cancer and 3,471 health controls, and their use of 28 isoflavone supplements, were used for the study. 15 of these supplements were multiple ingredient, or brand name supplements, whilst the other 13 were single ingredients. Women who took more than 0.676mg of supplements had a consistently reduced risk of breast cancer (28%) and this reduction increased to 43% when these supplements were used for one to five years. Yet there was no link between using a lower content isoflavone supplement.

The researchers explained, ‘Our findings of reduced post-menopausal breast cancer risk among women who ever used isoflavone supplements are compelling, however study limitations must be considered. In addition to the general limitations of case control study designs, our results were based on small numbers of supplement users, especially in subgroup analyses, and are to be viewed with caution.’

They concluded by saying, ‘Future research, especially in large prospective studies of pre- and post-menopausal women, should ascertain supplements taken concurrently, sequentially and consistently, as well as gaps in use. These data will support the derivation of average daily isoflavone intakes from supplements and allow comparison with those from foods.’