Obesity and Breast Cancer: What Is the Relationship?

Published on January 06, 2023

Medically reviewed by Archana Sharma, DO, FAAP

More than 70% of American adults have overweight or obesity. Overweight and obesity have been linked to an increased risk for some cancers. People who have been through menopause and have overweight or obesity have an increased risk of developing breast cancer.

Having more fat tissue increases estrogen levels. Higher insulin levels are more common in people who have overweight or obesity as well. These factors are believed to contribute to breast cancer risk.

While research shows a link between increased body fat and higher breast cancer risk, obesity and cancer are complex. They involve an interaction between genetics, environment, and lifestyle, making it difficult to pinpoint an exact cause and effect. More studies are being conducted to examine more precisely how obesity and breast cancer are linked.

This article discusses how obesity is believed to influence breast cancer risk and how having obesity affects people who are being treated for breast cancer.

People holding pink ribbons for breast cancer awareness — kali9 / Getty Images

Connection Between Obesity and Breast Cancer

Research has found a link between obesity and an increased risk of developing breast cancer, particularly for people who have been through menopause. Still, it has not been established definitively that obesity causes breast cancer. There may be other commonalities in people who have obesity that also influence cancer risk.

Even with the accepted link between obesity and breast cancer risk, some factors can influence an individual's risk.

For example, some studies suggest there is an increased risk in people who gained weight as an adult rather than in people who have had overweight or obesity since childhood. It's also been suggested that extra fat around the waist area poses a greater risk than extra fat in the thighs and hips.

Having overweight or obesity can also increase the risk of breast cancer returning after treatment.

Research suggests obesity increases the risk of breast cancer in several ways.

Hormones

Extra body fat can cause increased levels of growth hormones. These hormones signal cells to divide more often, which raises the chances of cancer cells developing.

Fat cells also make the sex hormone estrogen. More fat cells mean a higher production of estrogen, which can raise the risk of the development and growth of hormone-receptor-positive (HR-positive or HR+) breast cancers.

After menopause, fat tissue becomes the predominant site of estrogen production. This means people who have obesity and who have been through menopause have higher levels of estrogen than those who are postmenopause and standard weight.

Obesity can also raise levels of the hormones insulin and insulin growth factor-1 (IGF-1), which can increase the chances of cancer developing.

Inflammation

Immune cells go to areas where there are more fat cells, which can lead to inflammation. This causes the cells to divide more quickly, which can increase the risk of cancer over time.

It's common for people who have obesity to experience chronic, low-level inflammation, particularly in white adipose (fat) tissue.

Risks

Obesity increases risks that come with breast cancer in a number of ways.

Risk of Developing Breast Cancer

Compared to people of standard weight, the risk for developing breast cancer in people who have overweight or obesity is:

0.8 times the risk premenopause
1.2–1.4 times the risk postmenopause (the risk increases as body mass index (BMI) increases)

Risk of Recurrence and Metastasis

People who have obesity and breast cancer:

Tend to have larger primary tumors at the time of diagnosis
Have an increased risk of developing lymph node metastases (when the cancer spreads to the lymph nodes)
Are up to 46% more likely to have distant metastases (when the cancer spreads to areas of the body farther from the primary tumor) 10 years after being diagnosed
Have approximately a 30% increased risk of recurrence (the cancer returning)
Have a higher risk of developing a second, unrelated cancer

Does Obesity Increase the Risk of Other Cancers?

Overweight and obesity have been linked to other cancers, including:

Uterine cancer
Prostate cancer
Pancreatic cancer
Gallbladder cancer
Thyroid cancer
Colorectal cancer (cancer of the colon and/or rectum)
Head and neck cancer
Esophageal cancer
Ovarian cancer
Kidney cancer
Liver cancer
Myeloma (a type of blood cancer)
Meningioma (a type of brain tumor)

Treatment and Management of Breast Cancer With Obesity

There is little evidence to show whether weight reduction during breast cancer treatment affects outcomes. Before making any changes, people who have obesity and breast cancer should talk to their healthcare provider about appropriate dietary changes during and after treatment.

The course of treatment for breast cancer is tailored to each individual, whether they have obesity or not. While people with obesity receive the same types of treatment as those without the condition, research has shown that obesity can have an effect on breast cancer treatments.

Surgery (Mastectomy, Lumpectomy, Reconstruction)

People who have obesity who undergo surgery for breast cancer:

Have an increased risk of complications from anesthesia
Have an increased risk of complications such as bleeding, surgical site infections, and lymphedema (arm swelling due to backup of lymph fluid)
May be advised against reconstructive breast surgery because of the increased risk of complications
May be less pleased with how the results look after reconstruction

Chemotherapy

People who have obesity:

May require higher doses of chemotherapy but may be underdosed
May experience less effectiveness from chemotherapy treatment

Co-Occurring Factors That May Contribute to the Link

Some factors that may contribute to the effect of obesity on breast cancer include:

Psychosocial factors: Obesity in people assigned female at birth is more common with lower socioeconomic status than with higher socioeconomic status. This can complicate their access to healthcare.
Stigma: Stigma can lead to fear, alienation, self-consciousness, and other feelings that cause people with obesity to avoid seeking medical treatment. This can mean a delayed diagnosis and/or improper adherence to treatment plans. People over age 40 with overweight or obesity are also less likely than people of standard weight to have had a mammogram in the prior two years.
Fat phobia and medical bias: Whether they are aware of it or not, medical professionals can hold negative attitudes toward people with obesity, which can affect how they perceive their patients and make decisions about medical care.
Racial disparities: Non-Hispanic Black women have a higher prevalence of obesity compared to other racial and ethnic groups in the United States. Non-Hispanic Black women are approximately 40% more likely to die of breast cancer, despite the fact that rates of breast cancer are similar among non-Hispanic White women and non-Hispanic Black women. Black women are more likely to be diagnosed at a later stage than White women and are less likely to receive stage-appropriate treatment. Black women with obesity face systemic inequalities related both to racism and weight bias.

Verywell Health prefers to use inclusive terminology. But when citing research or health authorities, the terms for sex or gender from those sources are used.

Prevention

While studies show a link between weight gain and increased breast cancer risk, the evidence on whether losing excess weight reduces your risk is less clear. It is difficult for researchers to examine the potential for reduced risk with weight loss because few adults lose weight and effectively keep it off for long enough to study them for an extended period.

What is known is that healthy lifestyle habits, even aside from weight loss, can help reduce cancer risk. These include:

Exercise: As little as 75 to 150 minutes of brisk walking per week has been shown to lower breast cancer risk.
Healthy eating: Eating a diet of a variety of nutritious foods is also important to improving or maintaining overall health.

If you do not have overweight or obesity, these lifestyle habits are still important for your health and keeping your risk of breast cancer lower.

Weight Loss

For some people, weight loss may improve their health and potentially lower cancer risk. This may be as little as 5% to 10% of their total body weight.

Before starting a fitness or weight loss plan, talk to your healthcare provider to ensure you are doing it safely.

Consider talking to a registered dietitian, a healthcare provider who specializes in weight loss, or other reputable weight loss professionals. They can help you develop healthy long-term lifestyle habits made for lasting change.

Cycling between diets, gaining and losing weight, has been linked to increased cancer risk. It's worth taking the time to make changes properly.

If you have a lot of weight to lose for your health, and find it challenging to do so through lifestyle changes alone, your healthcare provider may suggest bariatric surgery to help you meet your health goals.

Summary

Overweight and obesity have been linked to an increased risk of developing breast cancer, particularly after menopause. The exact cause and effect isn't known, but it's believed that hormones influenced by fat cells as well as inflammation commonly seen in people with obesity play a part.

Obesity may also influence the efficacy of cancer treatments. It's unclear if losing weight reduces breast cancer risk, but healthy lifestyle habits, such as eating a nutritious diet and exercising, have been shown to reduce the risk of breast cancer, with or without obesity.

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