Many women diagnosed with breast cancer live longer than ever, and the number of women who live with the disease for at least 5 years is growing.
We have analysed global research on the links between weight, diet, physical activity and a woman’s risk of death after a diagnosis of breast cancer.
Our review found strong evidence that a higher body weight after a breast cancer diagnosis increases a woman’s risk of death. We found some limited evidence that doing more physical activity lowers her risk of death.
Breast cancer in men is rare and all the studies reviewed focused on the disease in women only.
Our review included a number of risk factors related to body weight: body mass index (BMI), waist circumference and waist to hip ratio. For all 3 measures, higher levels are generally linked to greater health risks.
We found few studies that looked at the effect of BMI change or weight change, and those findings were not clear.
We reviewed 226 studies from around the world, comprising more than 456,000 women with breast cancer. Of them, 36,000 died including 21,000 who died from breast cancer.
For every 5-point (kg/m2) increase in BMI, the risk of dying of any cause was estimated to increase by 7%.
The risk of dying from breast cancer was estimated to increase by 10% and the risk of having a second primary breast cancer by 14% both for every 5-point increase in BMI (kg/m2).
We reviewed 108 studies from around the world, comprising more than 151,000 women with breast cancer. Of them, 14,900 died including 5,900 who died from breast cancer.
We reviewed 23 studies from around the world, comprising more than 39,000 women with breast cancer. Of them, approximately 5000 died including 2,000 who died from breast cancer.
Most studies looked at recreational physical activity, such as aerobics, walking and running, with limited studies on other types of activity.
The studies measured physical activity using metabolic equivalent of task (MET) – the rate at which the body uses energy (oxygen) during physical activity compared with the energy used at rest. One MET is equivalent to 3.5ml oxygen per kg of body weight per minute. 10 MET hours per week equates approximately to 75 minutes of vigorous activity or 150 minutes of moderate activity.
The estimated reduction in risk for every 10-unit MET-h/week increase in physical activity was 15% for all-cause mortality and 14% for breast cancer mortality. This was seen up to approximately 20 MET-h/week; at this level of physical activity there was 47% reduced risk of all-cause mortality and 38% of breast cancer mortality. There was little further reduction in risk with higher levels of physical activity.
Breast cancer was the most common cancer in 2020, and the leading cause of cancer death. There were 2.3 million cases and 700,000 deaths. Yet, in 2020, 7.8 million women worldwide had lived for at least 5 years after their breast cancer diagnosis.
This research builds on our previous work on breast cancer and cancer survivors. It helps us better understand how certain lifestyle and environmental factors affect women after a breast cancer diagnosis.
We want to support people to live healthily beyond a diagnosis of cancer, and encourage governments to implement policies that help people do that.
The review is part of our Global Cancer Update Programme, and the result of ongoing analysis of decades of evidence by world-renowned, independent experts from across the globe.
The review was carried out on our behalf by a team at Imperial College London, UK, and funded by our network of international charities.
People living with and beyond breast cancer should always consult their healthcare team before making any changes to their diet or physical activity routine.