Postmenopausal women with type 2 diabetes are nearly 30% more likely to be diagnosed with breast cancer, according to a meta-analysis.

Researchers with the International Prevention Research Institute in Lyon, France, analyzed the results of 40 separate studies that examined the potential link between diabetes and breast cancer. The studies involved more than 56,000 cases of breast cancer across four continents.

Postmenopausal women with type 2 diabetes had a 27% increased risk of breast cancer, according to the data. The researchers found no link among women of premenopausal age or those with type 1 diabetes.

The authors suggested a high body mass index, which often is associated with diabetes, may be an underlying factor.

"We don’t yet know the mechanisms behind why type 2 diabetes increases the risk of breast cancer," Peter Boyle, PhD, the study’s lead author and president of iPRI, said in a news release. "On the one hand, it’s thought that being overweight, often associated with type 2 diabetes, and the effect this has on hormone activity may be partly responsible for the processes that lead to cancer growth. It is also impossible to rule out that some factors related to diabetes may be involved in the process."

The study, scheduled for publication in the British Journal of Cancer, is part of an overall evaluation of the association between metabolic disorders and breast cancer, which iPRI is conducting. Researchers also are investigating preventive measures against breast cancer, such as physical activity.

The study abstract is available at www.nature.com/bjc/journal/vaop/ncurrent/full/bjc2012414a.html.