Metabolic Health May Trump BMI as Predictor of Breast Cancer Risk

Marc J. Gunter, PhD

A new study has shown that postmenopausal women who had insulin abnormalities were at an increased risk for breast cancer regardless if they were overweight or normal-weight individuals.

The study, published in Cancer Research, found that women who were overweight and insulin-resistant had an 84% greater risk of breast cancer than women who were overweight but not insulin-resistant. In addition, breast cancer risk was twofold greater for women who were normal weight and had high fasting insulin levels compared with those who were normal weight and had normal fasting insulin levels.

“These results suggest that metabolic health evaluated by, for example, insulin resistance, might be a better predictor of breast cancer risk than being overweight or obese,” lead author Marc J. Gunter, PhD, associate professor of cancer epidemiology and prevention in the Department of Epidemiology and Biostatistics at Imperial College London’s School of Public Health, said in a statement. “However, given that being overweight or obese significantly increases an individual’s risk of being metabolically unhealthy, it remains important that we all keep a healthy weight throughout life.”

The researchers analyzed data from 3327 nondiabetic women enrolled in the Women’s Health Initiative, a long-term study to investigate the most common causes of death, disability, and poor quality of life in postmenopausal women.

Among this subcohort of women with available data on insulin resistance and body mass index (BMI), 497 received a breast cancer diagnosis over a mean of 8.2 years of follow-up.

Information on height and weight was collected at enrollment, as was a sample of fasting blood. Women with a BMI at enrollment of 25 or more kg/m² were classed as overweight. Metabolic health was assessed using two measures: fasting insulin levels and the homeostatic model assessment (HOMA-IR) method for quantifying insulin resistance.

“Obesity is a significant risk factor for a number of types of cancer including postmenopausal breast cancer,” said Gunter. “Most, but not all, individuals who are obese have metabolic abnormalities including high levels of fasting insulin and insulin resistance, which means that their bodies produce the hormone insulin but do not use it effectively.”

The study also found that breast cancer risk was no different for overweight and normal-weight women who were metabolically healthy by both measures of metabolic health.

“Our data suggest that insulin resistance may be a significant factor in the development of breast cancer, irrespective of whether a woman is overweight or normal weight,” said Gunter. “However, we need to conduct further larger-scale studies, preferably ones that allow us to follow a woman’s metabolic health over time, to better understand this and to verify our current findings.”