New research from the Daffodil Centre, a partnership between the University of Sydney and Cancer Council NSW, has found that drinking alcohol and having overweight or obesity are associated with an increased risk of breast cancer among Australian women as they age.

The study analysed data from 12,782 women in the Australian Longitudinal Study on Women’s Health, linked with the Australian Cancer Database that tracked participants over more than two decades (1996–2019). During this time, 941 women (7.4 percent) were diagnosed with breast cancer.

“We found that women who consumed alcohol had a significantly higher risk of developing breast cancer compared to non-drinkers, regardless of how much they drank,” says Professor Xue Qin Yu, lead author on the study from the Faculty of Medicine and Health and Professor of Cancer Epidemiology, Research Methods at the Daffodil Centre. “Women who have overweight or obesity also faced a higher risk.”

In particular, women who had overweight or obesity had a 23 percent higher risk of breast cancer compared to those in a healthy weight range or underweight. The study also showed that the likelihood of developing breast cancer increased steadily over time for women who drank alcohol and those with higher body weight.

The research adds important Australian evidence to the growing body of international studies examining how lifestyle factors influence cancer risk over time. By using longitudinal data, the study was able to capture how changes in behaviours such as alcohol use and body weight impact breast cancer risk across different life stages.

Professor Yu says the findings highlight the importance of focusing on modifiable risk factors, particularly during mid-life. “These results reinforce that maintaining a healthy weight and reducing alcohol use can play an important role in lowering breast cancer risk over the long term,” he says.

The study did not find statistically significant associations between breast cancer risk and smoking, hormone replacement therapy (HRT), or oral contraceptive use, although these relationships remain complex and may vary across populations.

"Supporting women to maintain a healthy weight, reduce alcohol intake, and stay connected socially and access preventive care are all important steps to promote healthy lifestyles for women as they age and reduce the burden of breast cancer in our community.”