Obesity is known to increase the risk of breast cancer in postmenopausal women, but the reason for this has remained greatly unknown. A recent study has found that in postmenopausal women, high insulin levels greatly increased breast cancer incidence, and it’s speculated that obesity might be a leading contributor to high insulin levels.
Breast cancer, which kills more than 40,000 women in the United States each year, occurs the vast majority of the time in postmenopausal women. Obesity too, is more prevalent with age, though the obesity epidemic has extended in large amounts over past decades to all age groups.
While the specific link between obesity and breast cancer is unknown, researchers have speculated that hormonal imbalance that results from obesity, is likely the cause of increased breast cancer incidence. It was previously believed that raised estrogen levels in obese women was responsible for the higher occurrence of breast cancer, but the current researchers have found that raised insulin levels could be even more important. High insulin levels have the effect of “stimulating the growth of breast cells,” which could raise the risk of breast cancer in postmenopausal women.
Blood samples of 1,651 women, 835 having known breast cancer, and 816 randomly selected controls, were analyzed in the study. Among other things, BMI (body mass index, an obesity indicator), estrogen and insulin levels, were determined for each individual. It was then determined that women with the highest insulin levels (the top 25%), were 50% more likely to develop breast cancer than normal insulin patients. According to Dr. Marc Gunter, “women with the highest insulin levels in their blood were more than two times more likely to develop breast cancer than women with the lowest insulin levels.”
So how did the obesity-breast cancer relationship fit into this study? Dr Gunter expresses that “when we controlled for insulin, the association between obesity and breast cancer became much weaker. This means that a large component of that obesity-cancer relationship may be mediated by insulin levels.”
If correct, this is a major finding that could lessen the suspected impact of high estrogen levels on the development of breast cancer. In addition, it lays the foundations for new treatments and preventions of breast cancer in postmenopausal women. A possible treatment, which is not yet developed, would target insulin in breast cancer patients, potentially reducing breast cell growth. As a preventative technique, postmenopausal women should be more closely screened for high insulin levels, which if present, could be treated in order to help limit the risk of breast cancer development. Unfortunately, these techniques will likely only be applicable to non-diabetic women, because with diabetes, comes irregular insulin production and balance, characterized by decreased insulin sensitivity. Concludes fellow researcher Dr. Howard Strickler, “tt is also possible that screening non-diabetic postmenopausal women for high insulin levels could prove useful in identifying individuals at high risk for breast cancer.”
Source: Defeat Diabetes Foundation: Gunter, Marc. Strickler, Howard. Heller, Michael. Journal of the National Cancer Institute news release. January 2008.