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High insulin levels increased breast cancer risk in postmenopausal women
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Postmenopausal women with hyperinsulinemia were at least two times more likely to develop breast cancer compared with women with the lowest insulin levels. Interventions that target insulin and its signaling pathways may decrease breast cancer risk in these women.
Researchers with the multiyear WHI followed health outcomes in 93,676 postmenopausal women. In 2004, they selected a subset of more than 1,600 women without diabetes: 835 had incident breast cancer. They assessed fasting insulin levels, naturally occurring estradiol levels and BMI.
There was a positive association between insulin levels and risk for breast cancer (HR=1.46; 95% CI, 1.00-2.13 for the highest vs. lowest quartile of insulin level). Most of this effect was observed in the large subset of women from the WHI study who did not receive hormone therapy.
However, the association with insulin level varied by HT use. After controlling for multiple breast cancer risk factors, insulin levels were associated with breast cancer only among women who did not receive HT (HR=2.40; 95% CI, 1.30-4.41 for the highest vs. lowest quartile of insulin level). There was an association between obesity and risk for breast cancer among women who did not receive HT (HR=2.12; 95% CI, 1.26-3.58). However, this association was attenuated by adjustment for insulin.
J Natl Cancer Inst. 2009;101:48-60.