Much research has shown that being overweight or obese increases a woman’s risk of being diagnosed with hormone-receptor-positive breast cancer. Doctors don't completely understand why extra weight is associated with higher hormone-receptor-positive breast cancer risk. It’s likely that extra body fat increases levels of estrogen and other hormones. Higher hormone levels can increase breast cancer risk.
A study supports the link between excess weight and higher hormone levels. The study found that estrogen and testosterone levels dropped quite a bit when overweight and obese women lost weight. The results were published online May 21, 2012 in the Journal of Clinical Oncology. Read the abstract of Reduced-Calorie Dietary Weight Loss, Exercise, and Sex Hormones in Postmenopausal Women: Randomized Controlled Trial.
All the 439 overweight or obese, postmenopausal women, age 50 to 75, were considered sedentary before they joined the study. This means that the women said they exercised fewer than 100 minutes per week at a moderate level.
The women were randomly assigned to one of four groups:
- Low calorie diet group (diet-only group). The women ate 1,200 to 2,000 calories each day (depending on each woman’s starting weight) and less than 30% of the calories came from fat. The women in the diet-only group also occasionally met one-on-one with a dietitian, attended weekly dietitian-led group meetings, and kept daily food logs.
- Moderate to vigorous intensity exercise group (exercise-only group). The women did 45 minutes of moderate to vigorous intensity aerobic exercise (brisk walking, for example), 5 days per week for a total of 225 minutes of exercise per week. Some of the exercise was done in monitored workouts.
- Diet-plus-exercise group. The women followed both the low calorie diet AND did 225 minutes of moderate to vigorous exercise per week.
- Control group (no special diet or exercise regimen).
When the study ended after a year, the women in the diet-only and the diet-plus-exercise groups had lost about 10% of their weight at the study’s start. (So a woman in one of those groups who weighed 180 pounds when the study started lost about 18 pounds.)
The researchers measured the levels of several hormones when the study started and at various times during the study. At the end of the study, women in the diet-only and the diet-plus-exercise groups had much lower hormone levels compared to their levels at the start of the study. The women in diet-only and the diet-plus-exercise groups also had much lower hormone levels compared to the control group. The women in the diet-plus-exercise group had the largest drop in weight and hormone levels.
Levels of several estrogen-like hormones went down:
- estrone levels dropped 9.6% in the diet-only group and 11.1% in the diet-plus-exercise group
- estradiol levels dropped 16.2% in the diet-only group and 20.3% in the diet-plus-exercise group
- free estradiol levels dropped 21.4% in the diet-only group and 26.0% in the diet-plus-exercise group
Levels of the hormone testosterone also went down:
- free testosterone levels dropped 10.0% in the diet-only group and 15.6% in the diet-plus-exercise group
The researchers also measured changes in the levels of a protein called sex hormone binding globulin (SHBG). This protein attaches to sex hormones, such as estrogen and testosterone, and makes the hormones less active. SHBG levels increased 22.4% in the diet-only group and 25.8% in the diet-plus-exercise group. Other research has shown that higher levels of SHBG are associated with a lower risk of breast cancer.
The results of this study suggest that overweight and obese women have higher levels of hormones that can increase breast cancer risk; losing weight through changes in diet and exercise can lower these hormone levels and likely lower breast cancer risk as well.
This study offers more evidence that getting to and maintaining a healthy weight through diet and exercise is worth the effort. A healthy weight can improve your overall health, lower your risk of breast and other cancers, and make it more likely that you'll survive if you're diagnosed with breast cancer.
The National Institutes of Health offers an online BMI calculator so you can calculate your BMI. If your BMI is high, talk to your doctor about a safe and sensible plan to lose weight.
The Centers for Disease Control’s Healthy Weight pages offer information on losing weight and maintaining a healthy weight. You also can find tips on creating a healthy eating plan that includes exercise in the Breastcancer.org Nutrition pages.