Losing Weight Reduces Your Risk of Developing Breast Cancer

Breast cancer is the most common cancer in women.  You can’t live in the United States and be unaware of the impact that this disease has on us as a society.  The whole nation turns pink every November to remind us to stay vigilant.  “Early detection saves lives” is dutifully repeated in magazines and waiting rooms.  With one in eight women affected, almost all women have a family history of breast cancer.  

Some of the risk factors for developing breast cancer you cannot change, such as being female..  Age also plays a role –  the risk of developing breast cancer increases with advancing age.  You can’t do anything about your family history either.  

However, there are several risk factors that you can change to decrease your risk of developing breast cancer. We have known for a long time that physical inactivity (or a sedentary life) increases the risk of developing breast cancer.  Some types of hormones can also raise the risk.  Studies have also shown that a woman’s risk of developing breast cancer increases with the more alcohol she drinks.  And then there is obesity.

Obesity is associated both with a higher risk of developing breast cancer, particularly in postmenopausal women, and with worse disease outcome for women of all ages.  In fact, women with overweight or obesity face a 30 – 60% greater risk of developing postmenopausal breast cancer than women of normal weight.  Women with obesity have a lower survival rate and face a higher risk of breast cancer recurrence – even when treated appropriately.   Women with obesity experience more complications related to breast cancer surgery, radiation, and chemotherapy. Systemic chemotherapy and endocrine therapy is less effective, even when dosed appropriately to account for the excess weight. 

It’s not just having excess weight that seems to be important to risk.  Weight gained after the age of 18 seems to be more important than weight gained in childhood.  Even more important seems to be weight gained after menopause.  A recent study showed that women that gained 20 pounds or more after they entered menopause had a higher risk of breast cancer compared to those that gained little to no weight after menopause.  

While the association between breast cancer and excess weight has been well documented, until recently, we didn’t have adequate evidence to determine if that risk was reversible by losing some of the excess weight.  However, we now have the evidence.  A large study released in 2019 confirmed what we have long suspected.  Women who lose weight after the age of 50 and keep it off have a lower risk of developing breast cancer than those whose weight remains stable.  Furthermore, the larger the amount of the weight loss, the lower the risk of breast cancer goes.  

This new study showed that women who lost 2 to 4.5kg (about 4.4 to 10 lbs) had a 13% lower risk than women with a stable weight.  Women who lost 4.5 – 9 kg (10-20 lbs) had a 16% lower risk and women who lost 9kg or more (20+ pounds) had a 26% lower risk of developing breast cancer than those women whose weight remained stable.  And, that’s not all the good news. Data revealed that women who lost a significant amount of weight (20+ pounds) and then regained some (but not all) of that weight back, continued to have a lower chance of developing breast cancer than women with stable obesity.   

The big takeaway is this:  for people with excess weight, losing weight helps prevent breast cancer.  If we are unfortunate enough to develop breast cancer, being a healthy weight will improve our odds of beating the disease and decrease the risk that the cancer will come back after treatment.  

To all of my patients out there that have fought this fight and won – you are amazing!

Courtney Younglove, M.D.