Increased breast cancer risk for postmenopausal women previously has been linked to obesity and diabetes, researchers at the Albert Einstein College of Medicine of Yeshiva University said.
Both conditions involve insulin resistance, which causes increases in circulating levels of insulin. Insulin promotes cell division and breast tumor growth in animal models, so the researchers reasoned that elevated insulin levels could contribute to breast cancer risk in women, said their study, published in the International Journal of Cancer.
"Up to now, only a few studies have directly investigated whether insulin levels are associated with breast cancer risk, and those studies have yielded conflicting results," Geoffrey Kabat, a senior epidemiologist at Einstein said.
Kabat's team analyzed data on 5,450 women enrolled in the Women's Health Initiative, a study investigating the influence of a number of factors on women's health.
The researchers found women in the upper third for insulin levels were more than twice as likely to develop breast cancer when compared with women in bottom third for insulin levels.