The link between obesity and breast cancer

Obesity is clinically defined as a body mass index (BMI) of 30 or higher. Those with obesity have a heightened risk of developing “obesity-related” cancers. Thirteen types of cancer currently fall into this group and breast cancer is one of them. Obesity isn’t the sole risk factor for obesity-related cancers.

The link between obesity and breast cancer risk varies based on menopause status and breast cancer type. While people with obesity are about 1.3 times more likely to develop postmenopausal breast cancer, research suggests premenopausal women with obesity are less likely to get breast cancer. Experts are still trying to understand this inverse relationship; they don’t recommend weight gain as a way to prevent breast cancer on account of the health risks associated with obesity.

Obesity isn’t the only weight-related factor linked to an elevated risk of breast cancer. One study found that high body fat levels increase the risk of breast cancer, even when BMI is normal. More studies are needed to better understand this relationship.

In addition to being a risk factor for developing breast cancer, obesity is also associated with negative health outcomes after diagnosis. These include lower survival rates, shorter periods of time until disease recurrence, and worse treatment outcomes. 

Why obesity Is a risk factor

It’s useful to understand which processes might be involved in obesity’s relationship with breast cancer. Here are some possible mechanisms:

• Increased estrogen production: Higher estrogen levels are associated with elevated breast cancer risk. Excess adipose tissue, or fat tissue, can lead to a higher conversion of estrogen precursors to estrogen, which may elevate overall risk.
• Chronic inflammation: Chronic inflammation is gradual inflammation that occurs over a period of months or years. Obesity is a known cause of chronic inflammation, especially in adipose tissue, which can be associated with tumor formation and growth.   
• Metabolic factors: People with obesity are at greater risk for developing chronic conditions including insulin resistance, which is characterized by an impaired response to insulin. This means muscle, fat and liver cells can’t efficiently use glucose from the blood for energy. As a result, the pancreas over-produces insulin. Obesity-related inflammation is also thought to promote the development of insulin resistance. Higher levels of insulin resistance have been associated with a higher incidence of breast cancer and higher all-cause mortality. 

Mitigating obesity as a risk factor  

Obesity is a treatable risk factor for cancer. Treatment for obesity always includes diet changes and increased exercise. Exercise is a key component in weight management, and one 2018 study found that exercise, in general, is associated with a 13% lower risk of breast cancer. Exercise has also been shown to reduce recurrence of and death from breast cancer. Experts recommend 75 to 150 minutes of moderate-intensity activity, such as brisk walking, per week. On top of healthy lifestyle habits, it’s important to be proactive about preventive care and to keep up with recommended cancer screenings. If diet and exercise alone are unable to help you meet your weight loss goals, medications may help.