Can being overweight or obese cause breast cancer?

Your risk of breast cancer increases if you are overweight or obese after the menopause. 

Putting on weight throughout adulthood also increases your risk of developing breast cancer after the menopause.

  • The more weight you gain in your life, the higher your risk of developing breast cancer after the menopause
  • By keeping to a healthy weight, you can reduce your risk of breast cancer after the menopause

How much does weight affect breast cancer risk?

In a group of 100 women with a healthy weight range, about nine will probably develop breast cancer at age 50 or above. 

In a group of 100 obese women, about 11 or 12 will probably develop breast cancer.

So, being obese causes about two or three extra women out of every 100 to develop breast cancer at age 50 or above.

By keeping to a healthy weight throughout your life, you can reduce this risk.

Why does weight affect breast cancer risk?

Hormones such as oestrogen help some breast cancers to grow. After the menopause, the ovaries stop producing oestrogen, so levels in the body drop.

Women who are overweight or obese after the menopause have a higher level of oestrogen in their bodies, which may encourage the growth of some breast cancers. This is because the hormone is also made by fatty tissue.

Being overweight or obese also alters the levels of other hormones, including insulin (which regulates the amount of sugar in your blood). 

These changes might increase the chance of breast cancer developing.

Other benefits of maintaining a healthy weight

Maintaining a healthy weight throughout your life also reduces the risk of developing a variety of other health problems, such as:

  • Heart disease
  • Stroke
  • Type 2 diabetes
  • Dementia
  • Other types of cancer
Last reviewed: September 2019
Next planned review begins 2020

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