Soy and Breast Cancer

Soy linked to longer survival in Chinese women with breast cancer

JAMA 2009;302:2437-43 [PubMed Abstract]

Researchers studying the anticancer effects of soy have found a link
between high dietary intake and prolonged survival in Chinese women
with breast cancer. Women in the highest quarter of daily intake were
29% less likely to die (hazard ratio 0.71, 95% CI 0.54 to 0.92) and 32%
less likely to have a recurrence (0.68, 0.54 to 0.87) than women in the
lowest quarter. The inverse association with all cause mortality was
stronger for soy protein than for soy isoflavones and remained
significant through multiple adjustments for factors known to influence
survival including age, cancer stage, treatment, other dietary factors,
body mass index, menopausal status, and the hormone receptor status of
the tumour.

The 5042 participants lived in Shanghai and were recruited from the
Chinese cancer registry about six months after their cancer diagnosis.
They completed detailed food frequency questionnaires that measured
their daily intake of tofu, soy milk, soy beans, and other common soy

Their mean daily intake was equivalent to 47 mg a day of isoflavones, a
much higher figure than would be expected for women outside China, says
an editorial (p 2483). Women in the US, for example, eat between 1 and
6 mg a day, usually as supplements, meat substitutes, and processed
foods. It is hard to say whether the associations reported here will
translate well to other populations. This study does show that soy is
safe, however. Soy has heterogeneous effects on oestrogen metabolism,
leading to fears that it might encourage the growth of breast tumours.
That now seems unlikely.

© 2009 BMJ Publishing Group Ltd.

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