Researchers from the International Agency for Research on Cancer recently examined the link between excess weight and breast cancer risk in postmenopausal women.

The scientists focused specifically on women who developed cardiovascular disease to see how developing this affected breast cancer.

The findings showed an especially increased risk of breast cancer for every 5 kilograms per square meter increase in body mass index (BMI) in women who developed cardiovascular disease.

According to the American Center for Disease Control and Prevention nearly 74% of people living in the US have body mass index levels that indicate overweight or obesity. 

Nor is that that only in the US as in the UK 2023-2024 saw an increase from previous years to 64.5% of adults being classified as overweight or living with obesity. This has been a worryingly upward trend since 2015.  

Carrying excess weight can cause many health issues, such as type 2 diabetes and an increased risk of heart disease. 

Being overweight can even lead to a higher risk of developing breast cancer.   

A European perspective

A study appear in the American Cancer Society’s journal was led by researchers from the International Agency for Research on Cancer of the World Health Organization (WHO) in Lyon, France.

They set out to discover whether women who are overweight or have obesity who go on to develop heart disease or type 2 diabetes have an increased breast cancer risk. 

While type 2 diabetes did not increase breast cancer risk, the study revealed that women who developed cardiovascular disease had a 31% higher risk of breast cancer.  

Linking obesity, CVD, and breast cancer

While breast cancer can affect women of all ages, it affects postmenopausal women at higher rates.  

After women go through menopaus and the ovaries no longer produce oestrogen, the hormone continues to be produced from body fat, which includes cells in the breasts.

Too much oestrogen can increase the chance of abnormal cell growth, which may lead an increased risk for breast cancer.  

This was a large scale company to investigate links between breast cancer and heart disease in postmenopausal women. They used data from around 170,000 participants from two European studies and only included women who did not have a history of CVD, type 2 diabetes, or breast cancer.  

Body Mass Index (BMI) was the focus for the authors in the new study in terms of developing CVD, type 2 diabetes, and breast cancer. 

Significant results

At the beginning of the data collection, the average age of the participants from both data sets was around age 60, and obesity levels in one data set was 17% and the other was 21%. 

The participants were then followed up 11 years later and one discovery was that developing CVD more than doubles breast cancer risk

The researchers also found that having either an overweight or obese BMI level and developing CVD can increase the risk of developing breast cancer.

During the follow-up period, nearly 7,000 women developed breast cancer. The scientists learned that each 5 kilograms per square meter (kg/m2) increase in BMI was linked to a 31% increase in breast cancer risk for women with CVD.

This is significantly higher compared to the increased risk in women without CVD, which was a 13% higher risk. 

Developing type 2 diabetes did not increase the risk of developing breast cancer.

The leader of the research team, Heinz Freisling PhD explained how excess body weight can lead to chronic inflammation, high insulin levels, and abnormal cholesterol, all of which can damage blood vessels and contribute to heart disease.

 He summed it up saying that excess weight can cause biological changes in the body that can lead to both cardiovascular disease and breast cancer, including inflammation, insulin resistance, and dysregulated hormone levels.

How to reduce your risk 

Christopher Berg, MD who specialises in cardio-oncology at Expert tips on lowering heart disease, breast cancer risk at Orange Coast Medical Center, and who was not involved in the research, agreed that commented that the study shows that the risk of breast cancer associated with elevated BMI is increased in women who develop cardiovascular disease. 

He made some preventive recommendations that postmenopausal women who want to lower their breast cancer risk can take. 

None of this is new, but it helps to be reminded that regular physical activity, reducing alcohol and smoking and most importantly having a heart-healthy diet. 

One of the most effective for this is the DASH or Mediterranean diets.