Dr. Susan Love Research Foundation | Breast Cancer

The findings from a new study suggest that women with a BRCA gene mutation who lose weight between the ages of 18 and 30 have a lower risk of developing breast cancer.

The study, "Changes in Body Weight and the Risk of Breast Cancer in BRCA1 and BRCA2 Mutation Carriers," was published online in August 2005 in Breast Cancer Research.

Women who carry a mutation in the BRCA1 or BRCA2 gene have a 45–87 percent risk of developing breast cancer in their lifetime. Scientists are trying to determine what factors increase the risk of a woman with a BRCA genetic mutation developing the disease.

For this study, researchers began by recruiting women in Canada and the United States with either a BRCA1 or BRCA2 mutation. They then used a case-control design in which a woman who had developed breast cancer was matched according to type of BRCA mutation, year of birth, and country of residence with a woman who had not developed breast cancer. The researchers were able to study 1,073 matched pairs: 797 with a BRCA1 mutation and 276 with a BRCA2 mutation. All of the women were asked how much they weighed at ages 18, 30, and 40. They were also asked their weight at birth, their height, and how much they had ever weighed (excluding time when they were pregnant).

The researchers found that women with a BRCA1 mutation who lost at least 10 pounds between the ages of 18 and 30 reduced the risk of developing breast cancer between the ages of 30 and 40 by 65 percent—a statistically significant finding.

In women with a BRCA2 mutation, weight loss reduced the risk of developing breast cancer by 12 percent. This finding was not statistically significant, which means it could have happened by chance.

The average weight at age 18 for the BRCA1 mutation carriers who lost more than 10 pounds was 142.5 pounds. (The range was 115 to 230 pounds. Forty percent of the women weighed more than 150 pounds and 35 percent had a body mass index [BMI] greater than 25, which is considered to be overweight at age 18.) They lost, on average, 18.6 pounds by the time they turned 30.

The study found that losing weight did not appear to reduce a woman's risk of developing breast cancer after the age of 40. And weight change that occurred between the ages of 30 and 40 did not decrease or increase the risk of breast cancer occurring in either premenopausal or postmenopausal women.

The researchers also found that women with a BRCA1 mutation who gained 10 or more pounds and who had at least two full-term pregnancies had a 44 percent increased risk of breast cancer. The researchers note that "although pregnancy itself offers long-term protection against postmenopausal breast cancer in the general population, significant weight gain during pregnancy has been associated with an increased risk of developing breast cancer after the menopause."

Based on their findings the researchers conclude that "weight loss in early adult life (and not weight per se) decreases the risk of BRCA-associated breast cancer diagnosed at an early age. More specifically, the period between age 18 and 30 years appears to be a critical one when weight gain should be avoided in mutation carriers."

Susan says:
A growing body of research indicates that there appears to be an association between weight gain and breast cancer in postmenopausal women. As this study found, this also appears to be true for premenopausal women with a BRCA1 mutation.

The link between breast cancer and weight gain is not fully understood. But we do know that postmenopausal women who are overweight have higher circulating estrogen levels—and as we've known for some time, estrogen fuels breast cancer growth. Obesity also appears to impact insulin, glucose, and triglyceride levels, all of which may influence breast cancer risk, apart from the estrogen mechanism. In premenopausal women, whose ovaries make most of their estrogen, the connection between weight and circulating estrogen levels has not been seen.

This study found that for women with a BRCA1 mutation, weight loss that occurred between the ages of 18 and 30 reduced the risk of developing breast cancer between the ages of 30 and 40. Many women do not learn that they have a BRCA mutation until after they are 30, at which point, in this study, weight loss did not appear to decrease breast cancer risk. For that reason, as this study underscores, it is important for all women, especially those with a family history of breast cancer, to maintain a healthy weight.

There are factors that influence breast cancer risk that are beyond our control—such as whether a woman has a BRCA mutation. But trying to maintain a healthy weight through proper diet and exercise—and encouraging young women to do so—is a lifestyle choice that has many benefits, even if it doesn't reduce breast cancer risk.