(Medical Xpress)—Women with type II diabetes are nearly 30 per cent more likely to get breast cancer, according to results of a comprehensive review published in the British Journal of Cancer today (Friday).
The study, by researchers at the International Prevention Research Institute (i-PRI), Lyon, analysed the results of 40 separate studies examining the potential link between breast cancer and diabetes.
These studies involved over 56,000 cases of breast cancer across four continents and found that post-menopausal women with type II diabetes had a 27 per cent increased risk of breast cancer.
The increase in breast cancer risk seems to be restricted to post menopausal women with type II diabetes, as the research found no link between women of pre-menopausal age or those with type I diabetes.
The authors have also suggested that a high Body Mass Index (BMI), which is often associated with diabetes, may be an underlying contributing factor.
Professor Peter Boyle, President of i-PRI and lead author of the study, said: "Our study found a significantly increased risk of breast cancer in women who had diabetes, which was restricted to those of post-menopausal age.
"We don't yet know the mechanisms behind why type II diabetes might increase the risk of breast cancer. On the one hand, it's thought that being overweight, often associated with type II diabetes, and the effect this has on hormone activity may be partly responsible for the processes that lead to cancer growth. But it's also impossible to rule out that some factors related to diabetes may be involved in the process."
Being obese increases the risk of postmenopausal breast cancer by up to 30 per cent and more than 4,000 cases of breast cancer each year in the UK are linked to excess bodyweight.
Martin Ledwick, head information nurse at Cancer Research UK, said: "From this study, it's not clear whether there's a causal link between diabetes and the risk of breast cancer in post menopausal women.
"But as we know that having a high BMI can contribute to an increased risk of both type II diabetes and breast cancer, it makes sense for women to try and maintain a healthy weight.
"Anyone who is concerned should consult their GP for advice and consider changes to their lifestyle, such as increasing their level of physical activity and changes to their diet, to keep the risks as low as possible."
Explore further: Physical activity more likely to prevent breast cancer in certain groups
Boyle, P. et al. Diabetes and breast cancer risk: a meta-analysis. British Journal of Cancer14