Archive | January, 2017

Soy Isoflavones: Is age of exposure affecting your breast cancer risk?

23 Jan

By Emily Farrell


Edamame – Immature soybeans which are steamed or boiled. Image courtesy of Emily Farrell. 

Does increasing your level of soy consumption decrease your risk of breast cancer? Are the hormone levels in your body playing a role? Is the hormonal impact of soy responsible for increasing or decreasing your risk of breast cancer? The existing inconsistencies surrounding soy intake and breast cancer risk may soon be clarified by an exciting hypothesis that the age at which soy consumption begins may play a role (Messina, 2016).

Soy isoflavones are phytochemicals that naturally exist in soybeans (Messina, 2016). Better known as phytoestrogens, they can bind to estrogen receptors in the body and induce estrogenic or anti-estrogenic effects (Messina, 2016). Isoflavones are much less potent activators of the estrogen receptor than estrogen itself, and when they are present in the body in higher amounts than estrogen (typically following the consumption of soy), they can exert an overall anti-estrogenic effect (Messina, 2016). These anti-estrogenic properties of soy isoflavones are thought to contribute toward a reduction in breast cancer risk. So why are there still inconsistencies in the data surrounding this relationship? According to an exciting hypothesis, the age at which soy consumption begins may be the culprit!

An animal study conducted in 2002 investigated the impact of soy isoflavones on breast cancer risk in female rats following exposure at different time points during the life cycle (Lamartiniere et al., 2002). The study concluded that, in order for soy isoflavones to have a protective effect, exposure must occur during mammary gland development, that is, exposure must occur before puberty (Lamartiniere et al., 2002). However, the most protective effect was observed when intake occurred both before puberty and during adulthood (Lamartiniere et al., 2002). More recently, a study performed in 2011 also found that soy isoflavones reduce breast cancer incidence following exposure before puberty in mice (de Assis et al., 2011).

What about human exposure to soy isoflavones before puberty? The Shanghai Women’s Health Study published in 2009, which involved greater than 70,000 Chinese women, investigated the association between breast cancer incidence and dietary soy intake during adolescence and adulthood (Lee et al., 2009). The study concluded that a high level of soy consumption (equating to approximately 50 mg of soy isoflavones/day) during adulthood was related to a reduced risk of breast cancer and adolescent soy consumption showed similar results (Lee et al., 2009). The most pronounced association, however, was observed in women who consumed consistently high levels of soy during both adolescence and adulthood (Lee et al., 2009). These results concur with animal data and provide evidence of a reduction in adult cancer relating to adolescent soy consumption (Lee et al., 2009). A follow up study using the same data from the Shanghai Women’s Health Study investigated the incidence of premenopausal breast cancer compared to postmenopausal breast cancer based on age of exposure (Baglia et al., 2016). In this case, it was found that high soy consumption during both adolescence and adulthood was related to a reduced risk of premenopausal breast cancer, while high soy consumption solely during adulthood related to reduced risk of postmenopausal breast cancer (Baglia et al., 2016). These findings support that hormonal status is a factor in the timing of exposure hypothesis.

Research is ongoing in this area to understand the underlying biological mechanisms by which soy intake can decrease breast cancer risk, to advance the knowledge surrounding soy intake and its association with breast cancer risk, and to possibly improve a breast cancer prognosis following a diagnosis (Messina, 2016).

If you’re looking to reduce your breast cancer risk and you’re already past your adolescent glory days, increasing your soy consumption now definitely won’t hurt! I know I’ll be adding some more soybeans into my diet.


Baglia, M.L., Zheng, W., Li, H., Yang, G., Gao, J., Gao Y-T., and Shu X-O. (2016). The association of soy food consumption with the risk of subtype of breast cancers defined by hormone receptor and HER2 status. International Journal of Cancer, 139: 742–748.

de Assis, S., Warri, A., Benitez, C., Helferich, W., and Hilakivi-Clarke, L. (2011). Protective effects of prepubertal genistein exposure on mammary tumorigenesis are dependent on BRCA1 expression. Cancer Prevention Research, 4(9): 1436–1448.

Lamartiniere, C. A., Cotroneo, M.S., Fritz, W.A., Wang, J., Mentor-Marcel, R., and Elgavish, A. (2002). Genistein chemoprevention: timing and mechanisms of action in murine mammary and prostate. The Journal of Nutrition, 132(3): 552S-558S.

Lee, S-A., Shu, X-O., Li, H., Yang, G., Cai, H., Wen, W., Ji, B-T., Gao, J., Gao, Y-T., and Zheng, W. (2009). Adolescent and adult soy food intake and breast cancer risk: results from the Shanghai Women’s Health Study. The American Journal of Clinical Nutrition, 89(6): 1920-1926.

Messina, M. (2016). Soy and health update: Evaluation of the clinical and epidemiologic literature. Nutrients, 8(12).