Obesity can cause various health issues – like type 2 diabetes and an increased risk of heart disease – and even lead to a higher risk of developing breast cancer, suggest researchers from the International Agency for Research on Cancer of the World Health Organisation (WHO).
Investigating whether overweight or obese women who then develop heart disease or diabetes have more risk of breast cancer, they found that while type 2 diabetes did not increase breast cancer risk, the women who developed cardiovascular disease (CVD) had a 31% higher risk of breast cancer, reports MedicalNewsToday.
The study appears in the journal Cancer.
To learn more about breast cancer and heart disease in postmenopausal women, the authors used data from around 170 000 participants from two European prospective cohort studies, including only women who did not have a history of CVD, type 2 diabetes, or breast cancer.
They reviewed various health metrics, including BMI, which is not always the best measure of health as it does not take into account sex, age, fat location, or muscle mass.
However, as a more established measure, BMI was the focus for the authors in terms of developing CVD, type 2 diabetes, and breast cancer.
At the beginning of the data collection, the average age of the participants from both data sets was around 60: obesity levels in one data set were 17% and the other, 21%.
Both cohorts had a median follow-up of around 11 years. Some of the data the researchers reviewed from that time included whether the participants developed CVD, type 2 diabetes, or breast cancer.
They 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 of the women developed breast cancer.
The scientists learned that each 5kg per square metre (kg/m2) increase in BMI was linked to a 31% increase in breast cancer risk for those with CVD.
This is significantly higher than 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, said 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 said body fat (adipose) tissue secretes hormones, such as leptin, which can have an impact on blood pressure and heart rate.
“Leptin also stimulates cell division, in particular in breast tissue, and suppresses immune responses,” he added. “These mechanisms are also risk factors for breast cancer, with the exception of blood lipid levels.
“In short, excess adiposity 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.”
Christopher Berg, MD, a non-interventional cardiologist specialising in cardio-oncology at MemorialCare Heart and Vascular Institute at Orange Coast Medical Centre, said: “This study shows that the risk of breast cancer associated with elevated BMI is increased in women who develop cardiovascular disease.”
Berg, who was not involved in the research, said the findings highlight the potential of preventing atherosclerotic cardiovascular disease, not only to reduce heart-related outcomes but also as a strategy to reduce breast cancer risk.
“The study reinforces the importance of managing cardiovascular risk factors and maintaining a healthy weight to lower breast cancer risk,” he added.
Study details
Body mass index and breast cancer risk among postmenopausal women with and without cardiometabolic diseases: Findings from two prospective cohort studies in Europe
Emma Fontvieille, Anna Jansana, Laia Peruchet-Noray et al.
Published in Cancer on 15 July 2025
Abstract
Background
Adiposity, measured by body mass index (BMI), is a known risk factor for postmenopausal breast cancer. However, whether the association of BMI with breast cancer risk differs among women with and without cardiovascular diseases (CVDs) or type 2 diabetes (T2D) is uncertain.
Methods
This study used individual participant data from the European Prospective Investigation into Cancer and Nutrition (EPIC) and UK Biobank (UKB) that included 168,547 postmenopausal women who were free of cancer, T2D, and CVD at recruitment. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated with multivariable-adjusted Cox regression for associations between BMI and incident breast cancer by T2D and CVD status. Incidence rates per 1000 person-years and rate differences between observed and expected joint associations of adiposity and CVD or T2D for breast cancer were estimated. Study-specific estimates were meta-analysed.
Results
After a median follow-up of 10.7 years in EPIC and 10.9 years in UKB, 6793 postmenopausal women developed breast cancer. In the meta-analysis of both cohorts, BMI (per 1-SD increment, 5 kg/m2) was more strongly associated with breast cancer risk in women with CVD (HR, 1.31; 95% CI, 1.16 to 1.47) than in women without CVD (HR, 1.13; 95% CI, 1.11 to 1.16) (pinteraction = .02). T2D did not modify breast cancer risk (pinteraction = .33). The meta-analysed joint association of overweight or obesity (BMI, ≥25 kg/m2) and CVD led to 1.53 (95% CI, 0.35 to 2.71) more cases of breast cancer per 1000 person-years than expected but no such joint association was observed with T2D.
Conclusions
Adiposity-associated risk of breast cancer was substantially higher among women with CVD as compared to those without CVD.
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