While weight and body composition have long been associated with cancer risk, researchers in South Korea have evidence that the amount of weight gained and possibly how quickly the weight is added could increase the risk of breast cancer.

The database study explored the Korean National Health Insurance Service to identify premenopausal and postmenopausal weight gain and breast cancer rates. The data was gathered over a 5-year period between 2009 and 2014 and included more than 2 million women.

Weight Gain and Breast Cancer by the Numbers

Working off the extensive database, researchers calculated two body composition metrics. They found the percentage changes in weight and the percentage increase in waist circumference in women over 3 screenings over the 5-year window.

Researchers followed up with women over the next several years, the average of which was 6.9 years. They found breast cancer more common in postmenopausal women who experienced weight gain over two consecutive screenings. Women who lost weight saw a reduced risk of breast cancer when losing weight in two consecutive screenings.

Research also established that waist circumference reduction was also associated with a reduced risk of breast cancer.

Related: What Is Breast Cancer?

Weight-Related Risk Is Growing

According to the CDC, more than 70% of Americans are overweight. Unhealthy body weight, including obesity, decrease quality of life and can lead to high blood pressure, diabetes and certain kinds of cancer.

Being overweight increases the risk of breast cancer for women, particularly postmenopausal women. The Korean study confirms what oncologists have hypothesized for decades.

Why Does Weight Increase Breast Cancer Risk?

An increased amount of fatty tissue uniquely impacts the endocrine system. For many women, increased fat tissue leads to elevated estrogen and insulin levels, two hormones associated with cancer. Fat in the waist area, as measured by body fat calipers or waist circumference, is also believed to be more dangerous than fatty tissue stored in other body parts like the thigh or hip.

Move to Prevent Breast Cancer

Breast cancer is not entirely preventable. There are some genetic variables to a breast cancer diagnosis, but women can reduce their risk by achieving and maintaining healthy body weight. Speak with your doctor to determine a healthy weight for your height and build and make a plan to reach that goal. Losing as little as 5%-10% of body weight can improve your quality of life and reduce the risk of weight-related diseases.

Stay up-to-date with LessCancer.org by following our blog.