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

This article is most relevant for:
High risk women with a BRCA mutation or a close relative with a BRCA mutation

This article is also relevant for:

Checked People with a genetic mutation linked to cancer risk

Checked Previvors

Checked Women under 45

Checked Special populations: Women at high risk for breast cancer

Be a part of XRAY

Relevance: Medium


Strength of Science: Medium

Strength of Science

Research Timeline: Human Research

Research Timeline

Rating Details

Printer Friendly Page

Many treatments that lower estrogen levels also reduce breast cancer risk. Unfortunately, these treatments are also associated with negative side effects. A recent study looked at the effect of regular aerobic exercise on the estrogen levels of women who are at high risk for breast cancer. (11/14/2015)


At a glance Questions for your doctor
Findings     In-depth                 
Clinical trials Limitations
Guidelines Resources and references


This study is about:

How aerobic exercise affects estrogen 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 estrogen 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 estrogen levels than women who did not exercise regularly.

What does this mean for me?

This study looked only at the effect of exercise on estrogen 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 estrogen levels, which may reduce breast cancer risk. This is most likely to be relevant only in women whose cancer cells use estrogen receptors (ER), allowing estrogen to spur the growth of ER-positive breast cancer.  Many high-risk women, including those with BRCA1 mutations, develop triple-negative breast cancer, which does not utilize the estrogen receptor; this suggests estrogen 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.

Expert Guidelines

The National Comprehensive Cancer Network sets recommendations on weight management, nutrition and physical activity for cancer survivors. General principles of physical activity include: 

  • Physical activity and exercise recommendations should be tailored to the individual survivor’s abilities and preferences
  • Physical activity for cancers survivors:
    • Overall volume of weekly activity sould be at least 150-300 minutes of moderate-intensity activity or 75 minutes of vigorous activity or equivalent combination spread out over the course of the week
    • Two to three sessions per week of strength/resistance training that include major muscle groups
    • Stretch major muscle groups at least two days per week
  • Engage in general physical activity daily (eg. Taking the stairs, parking in the back of parking lot)
    • physical activity includes exercise, daily routine activities, and recreational activities
  • Avoid prolonged sedentary behavior (eg. Sitting for long periods)

Questions To Ask Your Health Care Provider

  • 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



Study background:

Some types of cancer need the hormone estrogen to grow. Because of this, many breast cancer treatments and risk management strategies focus on reducing estrogen levels. Past studies have shown that BRCA 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 estrogen levels in women at high risk for breast cancer. Rather than ask women how often they exercised, this study measured women’s estrogen 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 estrogen 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 BRCA mutation OR a first-degree relative (mother, father, sibling) with a BRCA 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 estrogen levels, and the final 5 months used to monitor changes in their estrogen 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 estrogen levels by about 4% at the first day of menstrual bleeding (the follicular phase).
  • exercise did not affect estrogen 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 estrogen levels seen would be maintained is unknown.

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


The results of this study show that exercise reduces estrogen levels, meaning that it might perhaps reduce risk of breast cancer, particularly in women who have the estrogen 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 estrogen 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 estrogen levels as much as removing ovaries or taking medications such as tamoxifen or raloxifene. Additionally, medications have been tested in randomized 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

(back to top)


Back to XRAY Home

Search XRAY studies and articles

Back to XRAY Home

FORCE:Facing Our Risk of Cancer Empowered