How does your body weight affect your breast cancer
risk?
Maintaining a healthy weight is one of the best things you can do for your health.
However, the percentage of Americans who are overweight or obese is higher than ever.
Currently, about 72 percent of men and 64 percent of women in the U.S. are overweight
or obese (defined as a body mass index (BMI) of 25 or higher).1
What is BMI?
BMI is a ratio of weight (in kilograms) and height (in meters):
Weight
_____________________
(Height)2
Because BMI includes a measure of height, it gives better comparisons of body weight
status among a group of people than weight alone. For example, two people may weigh
the same amount, but one may be tall and lean and the other may be short and stout.
Even though they have the same weight, they would have different BMI and you would
be able to compare their body weight status more easily. For this reason, BMI is the
measure most commonly used in research studies on weight and health.
Calculate your BMI.
Being overweight or obese is linked to many types of cancer, including postmenopausal
breast cancer. Understanding how body weight and weight gain affect your risk of breast
cancer both before and after menopause may be a good first step in making healthy
lifestyle choices.
Body weight and breast cancer risk
Body weight and its effects on breast cancer depend upon whether a woman has gone
through menopause.
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Before menopause, being overweight modestly decreases the risk of breast
cancer.2-5
After menopause, being overweight increases the risk of breast cancer.2-6
Premenopausal breast cancer risk
Before menopause, women who are heavier have a 20 to 38 percent lower risk of
developing breast cancer compared to leaner women.3,5,7 This benefit is not well
understood and may be limited to estrogen receptor-positive (ER+) breast cancers.8
Although being overweight seems to offer modest protection against breast cancer in
premenopausal women, weight gain should be avoided. Most breast cancers occur after
menopause, and any weight you gain before menopause you will likely carry into your
postmenopausal years.
Postmenopausal breast cancer risk
Women who are heavier have a 20 to 60 percent higher risk of postmenopausal breast
cancer compared to leaner women.2-6
Similar to premenopausal weight, body weight after menopause may have the most
impact on the risk of ER+ breast cancers. A meta-analysis that combined the results of
four studies found postmenopausal women who were heavy had a 70 percent greater risk
of ER+ breast cancer compared to those who were lean. However, these heavier women
did not have an increased risk of estrogen receptor-negative (ER-) breast cancers.9
Why might body weight affect breast cancer risk?
Although we do not fully understand why breast cancer risk differs in pre- and
postmenopausal women, the hormone estrogen likely plays a role. Women with higher
estrogen levels have an increased risk of breast cancer (learn more).10
In premenopausal women, most of the estrogen in the body is produced in the ovaries.
Weight has little effect on this estrogen. In postmenopausal women, the main source of
estrogen is fat which contains an enzyme that makes estrogens. So, heavier
postmenopausal women tend to have higher estrogen levels compared to leaner
postmenopausal women. This extra estrogen likely explains the increased breast cancer
risk among postmenopausal women who are overweight.11
Women who are heavier also tend to have higher levels of insulin in their bodies
compared to leaner women.12 Some studies have shown an increased risk of breast cancer
among postmenopausal women with high levels of insulin including women with type 2
diabetes.13-16 Among premenopausal women, findings on a possible link between insulin
levels and breast cancer risk are less clear.17-18 These topics are still under study.
Weight gain during adulthood and breast cancer risk
Postmenopausal breast cancer
Weight gain after age 18 appears to increase the risk of breast cancer in postmenopausal
women. Study findings show the more weight women gain, the more their breast cancer
risk tends to increase.6,19-21 For example, findings from the Nurses Health Study showed
women who gained about 10 to 45 pounds after age 18 had a 15 percent greater breast
cancer risk compared to women with little weight change. Women who gained more than
55 pounds after age 18 had a 45 percent increase in postmenopausal breast cancer risk.21
It’s not just the weight gained from age 18 that seems to be important to risk. Even
among women who gain weight after menopause, there appears to be an increased risk of
breast cancer. The National Institutes of Health-American Association of Retired Persons
Health Study found women who gained more than 66 pounds after age 50 had an 89
percent increased risk of breast cancer.6
Premenopausal breast cancer
To date, only a few studies have addressed weight gain and premenopausal breast cancer
risk. Most have shown no link between the two, but this topic is still under study.22-24
Weight loss and breast cancer risk
The good news is that for women who are overweight, losing weight may help lower
breast cancer risk. And, it’s never too late to start. One large study found women who lost
four to 11 pounds after menopause had more than a 20 percent lower risk of breast cancer
compared to women whose weight did not change.21
According to Dr. Jennifer Ligibel, assistant professor of medicine at Harvard Medical
School, “Many women ask how they can lower their risk of breast cancer. One of the
important things about identifying excess weight as a risk factor for breast cancer is that,
unlike many of the other risk factors for breast cancer that women can't do anything about
(like being a woman or getting older), weight is something that a woman can modify to
potentially lower her risk of developing breast cancer. Although losing weight isn't easy,
it might help a woman avoid breast cancer. We also know that keeping your weight in a
healthy range helps to lower the risk of many other health problems such as heart disease
and diabetes. A healthy diet and moderate exercise should be part of a healthy lifestyle
for all women.”
Future directions in research
During adolescence, girls enter puberty and their breasts begin to mature. Because this is
an important time of breast growth and development, body weight during adolescence
may play an early role in breast cancer risk. Some study findings suggest girls who are
heavier than average during adolescence have a decreased risk of pre- and
postmenopausal breast cancer.23,25-26 And, some findings suggest girls who are leaner
than average also have a decreased risk of breast cancer.25 These relationships are under
active study and reflect the complex links between body weight throughout life and
breast cancer risk.
The benefits of maintaining a healthy weight
Avoiding weight gain not only helps protect against breast cancer, it also has many other
health benefits. Compared to women who are overweight or obese, women with a healthy
weight have a lower risk of pancreatic, endometrial, ovarian, kidney and other types of
cancer.5,27-30 And, they are less likely to develop other health problems, including:31-32
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Heart disease
Stroke
Type 2 diabetes
High blood pressure
Liver and gallbladder disease
Sleep apnea and other breathing problems
Healthy lifestyle choices-it’s never too late to change
With so many risk factors for breast cancer out of our hands (like age, being female and
genetic factors), body weight is one of the few things most of us can try to control. And,
making healthy lifestyle choices has benefits at any age. Getting regular physical activity
and eating a balanced diet are the best ways to avoid weight gain and maintain a healthy
weight at any point in life.
In our busy lives, making healthy choices can be easier said than done. Fortunately, there
are many resources available to help you plan a healthy diet and make simple changes to
your daily life to increase activity. Your health care provider is a good place to start.
And, many websites offer tips on adopting a healthier lifestyle, including:
Centers for Disease Control and Prevention (CDC)
Find tips on healthy ways to prevent weight gain or lose weight.
http://www.cdc.gov/healthyweight/index.html
Department of Agriculture’s ChooseMyPlate.gov
Create a personalized daily food plan (designed to maintain or lose weight) and find tips
on balancing calories and making healthy food choices.
http://www.choosemyplate.gov/
National Heart, Lung, and Blood Institute (NHLBI)
Find a menu planner, tips on being physically active and other tools for maintaining a
healthy weight.
http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/tools.htm
References
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