Black women diagnosed with breast cancer who also have central obesity — excess body fat in the abdominal area — were more likely to die from breast cancer or any other cause than similar women who didn’t have central obesity, according to a study.
The research was presented on June 4, 2021, at the American Society of Clinical Oncology (ASCO) Annual Meeting and published online on the same day by the journal JAMA Oncology. Read the abstract of “Association of Body Mass Index, Central Obesity, and Body Composition With Mortality Among Black Breast Cancer Survivors.”
Link between excess weight and cancer
The International Agency for Research on Cancer (IARC) has linked 13 types of cancer with being overweight and obese:
- meningioma (a type of brain tumor)
- multiple myeloma (cancer that forms in a type of white blood cell)
- adenocarcinoma of the esophagus (cancer in the cells of the mucus-secreting glands of the esophagus)
- thyroid cancer
- postmenopausal breast cancer
- gallbladder cancer
- stomach cancer
- liver cancer
- pancreatic cancer
- kidney cancer
- ovarian cancer
- uterine cancer
- colorectal cancer
Women are considered overweight if they have a body mass index (BMI) of 25 or higher. Women are considered obese if they have a BMI of 30 or higher. Women who are overweight or obese have a higher risk of being diagnosed with breast cancer than women whose BMI ranges between 18.5 and 24.9, especially after menopause. Being overweight also can increase the risk of breast cancer coming back (called recurrence by doctors) in women who’ve been diagnosed with the disease.
Scientists believe this higher risk is partly because fat cells make estrogen. Extra fat cells mean more estrogen in the body, and estrogen can make hormone-receptor-positive breast cancers develop and grow. Scientists also have recently found that extra fat cells can trigger long-term, low-grade inflammation in the body. Chronic inflammation has been linked to a higher risk of breast cancer recurrence. The proteins secreted by the immune system seem to stimulate breast cancer cells to grow, especially estrogen-receptor-positive breast cancer in postmenopausal women.
Tools to measure excess weight and body composition
Most studies looking at links between excess weight and breast cancer risks and outcomes use BMI to measure body fat. Researchers commonly use BMI because it’s calculated using a person’s height and weight, which are easy measurements to collect in large studies.
While BMI can be a reliable indicator of body fat for many people, it isn’t perfect and has limitations. BMI is calculated by multiplying your weight in pounds by 703 and then dividing that number by your height in inches. If you use the metric system, you can calculate your BMI by dividing your weight in kilograms by your height in meters. You also can find many BMI calculators online and enter your height and weight to get your BMI measurement.
One of the biggest limitations of BMI is that it doesn’t make a distinction between lean body mass and bones and fat — the calculation simply considers total weight. As a result, BMI may overestimate body fat in people who are tall or have a lot of muscle mass. And BMI may underestimate body fat in people who are older or who have lost muscle mass but have had no change in weight. In other words, it’s not a good tool for determining body composition.
BMI also isn’t a good way to figure out body fat distribution, meaning where the fat is located in the body.
Research has suggested that the location of fat may be important when determining excess fat’s link to cancer risk and cancer outcomes.
Waist and hip measurements are used to figure out if a person has central obesity, defined as a waist-to-hip ratio of more than 0.85 or a waist measurement of more than 88 cm (34.64 inches).
To figure out your waist-to-hip ratio, measure your waist at the smallest point, usually around your belly button. Measure your hips around the widest part. Divide your waist measurement by your hip measurement to calculate your ratio.
Obesity rates have been increasing faster in Black people who are cancer survivors compared with the general population. The researchers did this study to see if there were links between different ways of measuring body fat and survival in Black women who had been treated for breast cancer within the last year. The researchers also wanted to know if the location of any excess fat affected survival.
About the study
The researchers used information from Black women who were part of the Women’s Circle of Health and Women’s Circle of Health Follow-Up studies:
- The Women’s Circle of Health Study wants to figure out some of the reasons why Black women are diagnosed with breast cancer at a younger age and with more aggressive types of breast cancer than white women. The women in the study live in 10 New Jersey counties.
- The Women’s Circle of Health Follow-Up Study is looking at how obesity and other related health conditions affect survival in Black women who have been diagnosed with breast cancer. Again, all the women in the study live in 10 New Jersey counties.
About 10 months after the women were diagnosed with breast cancer, the researchers asked the women questions about:
- other lifestyle factors
- medical history
The researchers measured the women’s height, weight, waist circumference, and hip circumference and took a saliva sample from each woman.
The researchers also measured the women’s body composition using a portable bioelectrical impedance analysis scale. These devices send a weak electric current through the body — typically using electrodes placed on the body — and then measure the voltage to calculate the impedance, or resistance, of the body to the current. Most of the body’s water is stored in muscle. It’s likely that muscular people have more water in their bodies, which means the current flows quicker because there is less resistance. Fat and bone slow the current down because they contain much less water.
The researchers conducted interviews each year, either in the women’s homes or over the telephone, for 5 years after diagnosis.
This analysis looked at information from 1,891 Black women in the Women’s Circle of Health studies. All the women had been diagnosed with ductal carcinoma in situ (DCIS) or invasive breast cancer. The women’s average age at diagnosis was 54.5 years.
During about 6 years of follow-up, 286 of the women died; 175 (61.2%) of the deaths were because of breast cancer.
Of the 1,891 women analyzed:
- 1,060 women (56.1%) were considered obese
- 1,291 women (68.3%) had a waist-to-hip ratio of more than 0.85 and were considered to have central obesity
Compared with women who were not considered overweight or obese, women considered obese were more likely to:
- be older
- have a high school–level education or lower
- be diagnosed with estrogen-receptor-positive breast cancer
The researchers found that women considered obese were more likely to have worse survival rates:
- Women with the highest waist-to-hip ratio had a 61% increase in risk of dying from any cause, compared with women with the lowest waist-to-hip ratio.
- Women with the highest percentage of body fat had a 53% increase in risk of dying from any cause compared with women with the lowest body fat percentage.
- Women with the highest waist-to-hip ratio had a 64% increase in risk of dying from breast cancer compared with women with the lowest waist-to-hip ratio.
- Women with the highest percentage of body fat had an 81% increase in risk of dying from breast cancer compared with women with the lowest body fat percentage.
- Women with the highest BMI had a 33% increase in risk of dying from breast cancer compared with women with a BMI ranging between 18.5 and 24.9.
The researchers did not find any link between BMI categories and an increased risk of dying from any cause.
The link between high waist-to-hip ratio and the increased risk of dying from any cause tended to be stronger for:
- women diagnosed with estrogen-receptor-negative breast cancer
- women who were postmenopausal
- women who were age 60 or older
“Central obesity appears to increase risk for both premenopausal and postmenopausal breast cancer, as well as for all breast cancer subtypes,” said Elisa Bandera, M.D., Ph.D., of the Cancer Prevention and Control Program at the Rutgers Cancer Institute of New Jersey, during her presentation on the study. “For breast cancer survival, a higher BMI increases risk of mortality after a breast cancer diagnosis for both premenopausal and postmenopausal women.
“Among Black women, measures of body fat distribution and body composition measured by portable bioelectrical impedance seem to be a practical and feasible tool to identify women at higher risk of mortality,” she continued. “So the conclusion is that we know that racial ethnic disparities in obesity, body fat distribution, breast cancer risk, and survival persist and the causes are not well understood.”
What this means for you
If you’re a Black woman who has been diagnosed with breast cancer and are considered overweight or obese, the results of this study are very troubling.
If you’ve been diagnosed with breast cancer, you may want to consider making exercise and a healthy diet part of your daily routine. It may be hard for people who are recovering from breast cancer treatment to make these kinds of lifestyle changes. Some people say it helps to think of eating well and exercising as important parts of their treatment plans.
Other research suggests that it may be easier to make diet and exercise changes if you have someone to talk to you and motivate you. You may want to talk to your doctor or a registered dietitian about developing a healthy eating plan designed specifically for you and your needs.
It’s also a good idea to talk to your primary care doctor and your surgeon before you start an exercise program. Tell them the exercises you plan to do, and ask if there is anything you should avoid doing or if you should limit your range of motion in any way. It’s also a good idea to talk about any other medical conditions you might have (asthma or osteoporosis, for example) and how these conditions may affect your ability to exercise.
Losing weight can be hard, but as studies including this one strongly suggest, it can be very important for your health. If you’re considering a weight-loss plan, it’s also important to be nice to yourself and to not punish yourself.
Read more about Eating to Lose Weight After Treatment so you can learn how to assess your weight and create a healthy eating plan.
Read more about Exercise so you can learn about the benefits of working with a trainer and how to stick to an exercise routine.
Written by: Jamie DePolo, senior editor
Reviewed by: Brian Wojciechowski, M.D., medical adviser
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