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Women who have reached the menopause stage are subjected to higher risk of breast cancer.
Increased breast cancer risk for post-menopausal women has previously been linked to obesity and diabetes. Both conditions involve insulin resistance, which causes increases in circulating levels of insulin.
Since insulin is known to promote cell division and enhance breast tumour growth in animal models, Einstein College of Medicine scientists reasoned that relatively high insulin levels may contribute to breast cancer risk in women.
"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," says Geoffrey Geoffrey Kabat, senior epidemiologist at Einstein and the study's co-author.
"Those other studies were based on just a single baseline measurement of insulin, while our study involved analysing repeated measurements of insulin taken over several years - which provides a more accurate picture of the possible association between insulin levels and breast cancer risk."
Kabat and colleagues analysed data on 5,450 women enrolled in the Women's Health Initiative, a large multi-centre study investigating the influence of a number of factors on women's health.
Most of the women who had participated in the clinical trial part of the study and provided fasting blood samples at the initial stage and then after one year, 3 years and 6 years.
The remaining women, who were enrolled in a separate "observational" component of the study, provided fasting blood samples at baseline and at year three of the study. Among all these women, 190 cases of breast cancer were identified over eight years of follow-up.
The analysis revealed a strong association between elevated insulin levels and increased risk for breast cancer, said an Einstein release.
These findings were published in online in the International Journal of Cancer.
