| Soy intake and breast cancer risk
The results of our meta-analysis of 18 epidemiology studies of soy and breast cancer showed a modest statistically significant 14% absolute reduction in risk. To
give some perspective on the figure of 14% reduction in risk, it may be
useful to point out that for women
45-60 years old, the risk of developing breast cancer in the next 10 years
is about 2.5% to 4.5% (at least in the US; your rates may be slightly
lower). A 14% reduction in these rates would change the risk by only
about 0.4 - 0.6%, i.e. reduce the rates to about 2% to 4% Among women in Asian countries the reduction was somewhat smaller and not significant. However, inconsistencies among the studies raise questions about the true nature of the benefit. There was little or no evidence of a dose response; women in Western countries who eat relatively little soy experienced a reduction in risk that was equal to or slightly greater than Asian women who have much higher soy intake. Inconsistencies in the studies included variation in the type of soy measurement used, and in the degree to which other confounding factors were controlled. Soy intake may actually be a surrogate for other dietary or behavioral factors that reduce breast cancer risk. Furthermore, the effect of soy may depend on the timing of exposure; some animal studies suggest that early life exposure is protective, while adult exposure has yielded inconsistent effects. The above limitations indicate that the current data are not adequate to determine whether soy foods protect against breast cancer. Because this study did not provide a clear, strong indication of protection due to soy, we recommend against women using soy or isoflavone supplements to obtain very high intake of soy components. In fact, some data in tissue culture, animals, and short-term supplementation in women suggest effects of supplements that could potentially be harmful to the breast. We do not know enough about the long-term effects of high dose soy or isoflavone supplements in women, particularly those at high risk of breast cancer or breast cancer survivors. However, if women want to obtain potential benefits from soy they should eat actual soy foods, for example 100 g tofu, a glass of soy-milk, or a handful of soy nuts.
Bibliographical reference:
Bruce
J. Trock
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