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Study: Aerobic exercise lowers estrogen levels in premenopausal women at high risk for breast cancer

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This study is about:

How aerobic exercise affects levels in young women who are at high risk for breast cancer.

Why is this study important?  

Removing the ovaries and taking risk-reducing medications such as tamoxifen have been shown to reduce breast cancer risk; however, both are associated with short-term and long-term side effects.  Aerobic exercise does not have negative long-term consequences, and is an accessible activity for people, so understanding if exercise can also lower levels is the first step in determining whether or not it can be used to reduce breast cancer risk in young women who are at high risk for breast cancer.

Study findings: 

  1. Premenopausal women at high risk for breast cancer who participated in regular aerobic exercise for 5 months had lower levels than women who did not exercise regularly.

What does this mean for me?

This study looked only at the effect of exercise on levels in premenopausal women at high risk for breast cancer—it did not directly measure the effect on breast cancer risk.  Researchers found that exercise was associated with lower levels, which may reduce breast cancer risk. This is most likely to be relevant only in women whose cancer cells use receptors (ER), allowing to spur the growth of ER-positive breast cancer.  Many high-risk women, including those with mutations, develop , which does not utilize the receptor; this suggests levels might not be as relevant for these women.

Regardless of its effect on breast cancer risk, exercise is extremely beneficial for many aspects of health: it helps to control weight; prevent heart disease, diabetes and high blood pressure; boosts energy; and improves mood and sleep. Everyone is encouraged to talk with their health care providers about how they can make exercise part of their routine.  Women at high risk for breast cancer should continue to maintain a heightened breast cancer screening schedule with their health care provider even when engaging in an exercise program.

Posted 11/14/15

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Schmitz KH, Williams NI, Kontos D, et al. “Dose-response effects of aerobic exercise on among women at high risk for breast cancer: a .” Breast Cancer Research and Treatment. Published first online on October 28, 2015.


FORCE receives funding from industry sponsors, including companies that manufacture cancer drugs, tests and devices. All XRAYS articles are written independently of any sponsor and are reviewed by members of our Scientific Advisory Board prior to publication to assure scientific integrity.

This article is relevant for:

High risk women with a BRCA mutation or a close relative with a BRCA mutation

This article is also relevant for:


people with a genetic mutation linked to cancer risk

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Study background:

Some types of cancer need the hormone to grow. Because of this, many breast cancer treatments and risk management strategies focus on reducing levels. Past studies have shown that mutation carriers who reported exercising during adolescence had lower breast cancer risk or a delayed breast cancer diagnosis, suggesting that there might be a relationship between exercise and breast cancer risk. Dr. Kathryn Schmidt and colleagues at University of Pennsylvania investigated whether or not exercise could affect levels in women at high risk for breast cancer. Rather than ask women how often they exercised, this study measured women’s levels before they began an exercise program, and again 5 months after they participated in a monitored aerobic exercise program.

Researchers of this study wanted to know:

How exercise affects levels in premenopausal women at high risk for breast cancer.

Population(s) looked at in the study:

The study included 135 women, who at the start of the study:

  • had never had breast cancer.
  • had a mutation OR a (mother, father, sibling) with a mutation.
  • classified as high risk based on one of two models used to predict breast cancer risk
  • were between ages 18-50 and not in menopause.
  • participated in aerobic exercise no more than 75 minutes per week for six months prior to beginning the study.

Women were followed over 7 menstrual cycles, with the first 2 months used to establish their normal levels, and the final 5 months used to monitor changes in their levels when they participated in a prescribed aerobic exercise regimen. Women were placed into one of three groups:

  • One group continued their normal pattern of less than 75 minutes of aerobic exercise per week.
  • One group was assigned to a low level of aerobic exercise of 150 minutes per week.
  • One group worked up to a high level of aerobic exercise of 300 minutes per week.

Study findings: 

Hormone levels naturally change during different phases of the menstrual cycle. When researchers followed the women’s hormone levels at different stages of their menstrual cycle, they found that: 

  • every 100 minutes of exercise reduced levels by about 4% at the first day of menstrual bleeding (the follicular phase).
  • exercise did not affect levels after ovulation (the luteal phase).
  • exercise did not affect levels of progesterone, another hormone that can drive breast cancer growth in either phase.
  • For every 100 minutes of exercise, women showed a decrease of approximately 10% in a type of dense breast tissue called “fibroglandular tissue.” Previous studies have shown that increases in the amount of fibroglandular tissue correlate to increased breast cancer risk.


This was a relatively small study of women who were all at high risk for breast cancer. Further studies would be needed to compare the results in young women with average breast cancer risk.The study followed women for 5 months, so whether the reduction in levels seen would be maintained is unknown.

In addition, the short study period could only follow reduction in levels; women would need to be followed for a longer time to show that this reduction in levels is directly associated with a lower breast cancer risk. This was the most crucial limitation of the study—investigators looked at levels, yet changes in levels may not result in any change in breast cancer risk.


The results of this study show that exercise reduces levels, meaning that it might perhaps reduce risk of breast cancer, particularly in women who have the receptor (ER+). While the study was small, exercise is beneficial for many aspects of health other than cancer, and that is why all everyone is encouraged to discuss the best way to incorporate exercise into their regular routines. 

While a reduction in might reduce the risk of breast cancer developing, it is not yet a certainty. Patients should talk with their health care providers about all the methods they should be using to reduce their risk of developing cancer. In this study, exercise did not lower levels as much as removing ovaries or taking medications such as tamoxifen or raloxifene. Additionally, medications have been tested in clinical trials and demonstrated to reduce breast cancer risk, whereas exercise has not. Women at high risk for breast cancer are encouraged to discuss national guidelines that outline risk management for people at high risk for breast cancer with their health care providers and maintain a regular schedule of breast cancer screening.

Posted 11/14/15

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Expert Guidelines
Expert Guidelines

The American Cancer Society (ACS) guidelines on exercise, nutrition and weight for cancer prevention recommend the following: 

Diet and nutrition

  • Follow a healthy eating pattern, including:
    • foods that are high in nutrients in amounts that help you acheive and maintain a healthy body weight.
    • a variety of vegetables, fiber-rich legumes (beans and peas) and whole fruits in a variety of colors. Consume at least 2½ to 3 cups of vegetables and 1½ to 2 cups of fruit each day, depending on your calorie requirements. 
    • whole grains rather than refined grains. At least half of the grains you eat should be whole grains. 
  • A healthy eating pattern that limits or does not include:
    • red and processed meats.
    • sugar-sweetened beverages. 
    • highly processed foods and refined grain products.
  • It is best not to drink alcohol. People who choose to drink alcohol should:
    • have no more than 1 drink per day (women) or 2 drinks per day (men).


  • Exercise regularly.
    • Adults should get at least 150 minutes of moderate-intensity activity (equal to a brisk walk) or 75 minutes of vigorous activity (heart rate is increased, breathing is faster and you are sweating) each week, preferably spread throughout the week.
    • Physical activity has been shown to lower the risk of several types of cancer, including breast, endometrial, and colon. It also reduces the risk of other serious diseases including diabetes and heart disease.


  • Achieve and keep a healthy weight.
    • Being overweight or obese is a risk factor for many cancers, including breast, colon, endometrial and pancreatic. You can control your weight through regular exercise and healthy eating.

Other experts, including the following, also provide guidelines for exercise, nutrition and health: 

Updated: 07/19/2022

Questions To Ask Your Doctor
Questions To Ask Your Doctor

  • How much and what types of exercise should I be getting?
  • What are other ways to reduce my breast cancer risk?
  • Should I get a personal trainer? How do I find one? 

Open Clinical Trials
Open Clinical Trials

The following are studies focused on nutrition and cancer prevention. 

Multiple cancers

Breast cancer

Colorectal cancer

Visit our Featured Research Page and Research Search and Enroll Tool to find additional studies enrolling people with or at high risk for cancer.

Updated: 05/28/2023

Find Experts
Find Experts

The YMCA has a free program called Livestrong at the YMCA. This program includes a free 12-week membership and fitness training with certified exercise experts. You can search by zip code for a program near you.  

Updated: 08/18/2023

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