Estrogen and Breast Cancer: What’s the Relationship?

Dr. Jolene BrightenPublished: Last Reviewed: Estrogen Dominance, Sex Hormones Leave a Comment

Breast cancer isn’t exactly a topic any of us wants to discuss, but we need to. It’s so common that about 1 out of every 8 women in the U.S. will be diagnosed with breast cancer during her lifetime. With these numbers, it’s no surprise that many of us have been directly impacted by the diagnosis. 

It also means we have to work to decrease our risk. Risk factors for breast cancer vary from genetics to lifestyle factors, but topping the list is the close connection with the all-important sex hormone estrogen. 

Hormones fluctuate throughout a woman’s life, making her more or less susceptible to developing breast cancer at various times. But understanding this relationship can empower you to reduce your risk wherever possible. So let’s take a closer look together at estrogen, how it’s linked to breast cancer, and what lifestyle changes you can make to positively impact hormone balance.

What Does Estrogen Do For Your Health?

Before diving into its role in breast cancer, let’s begin by looking at all the beautiful things estrogen does for us. Aside from all the ways it impacts reproductive health, from your monthly cycle to pregnancy, estrogen plays a positive role in functions like:

  • Libido, fertility, and sexual health
  • Healthy stress response
  • Metabolism and body weight
  • Cholesterol balance and cardiovascular protection
  • Bone health
  • Cognitive function

Where Is Estrogen Made In Your Body?

Endogenous (“originating from within”) estrogen production primarily occurs in your ovaries, but it can also be made by your fat cells. Estrogens are actually a group of hormones, not a single hormone:

  • Estrone, produced mainly by fat cells and is the primary form after menopause.
  • Estradiol, made in ovaries and is the primary form during your reproductive years.
  • Estriol, the primary form during pregnancy.

The amounts and types of estrogen found in your body will vary during your menstrual cycle and throughout your life. These levels are influenced by external factors like your diet, medications, or endocrine disruptors (chemicals that disrupt your hormonal function and unfortunately can occur in your diet, cosmetics, and living environment). 

All of these factors can contribute to hormone imbalances that show up with symptoms of estrogen dominance, and for some women, in turn, increase the risk of developing breast cancer.

How Exactly Is Estrogen Linked To Breast Cancer?

While not always the case, estrogen does play a role in most common types of breast cancer — around 80% of cases according to evidence. While scientists and researchers are still working to build a better understanding of this complex area,  current research points to how much estrogen you are exposed to over time and how your cells respond to the hormone as being the main factors.

Estrogen Receptors 

Breast cancer (or any cancer) happens when specific cells grow or reproduce uncontrollably, damaging healthy tissue along the way. 

Estrogen can effect normal, healthy cell division through estrogen receptors on cells. These receptors act as a docking station on cells for estrogens to attach and send a message to make more cells (which is important during puberty and pregnancy for mammary gland development).

But with breast cancer, estrogen can bind with receptors on the outside of cancerous cells and send the same message to grow and reproduce. 

Estrogen Exposure Over Time Is Linked To Breast Cancer

The longer your body is exposed to estrogen throughout your life, the more it appears to increase your risk for estrogen-related breast cancer. This helps explain why most breast cancer diagnoses occur later in life, after a lifetime of exposure to estrogen.

But it gets more interesting. Even though breast cancer risk generally increases as you get older, if you start your period later in life (like after age 15), your risk goes down simply because you had a few extra years without estrogen. The opposite seems true for women who go through menopause later, as more years of estrogen exposure may actually increase the risk for breast cancer. 

See the connection? More estrogen equals more risk, according to current research.

Estrogen Dominance And Hormone Imbalance

Remember that estrogen isn’t all bad. You need it! But our sex hormones don’t exist alone in a bubble. The ratio of estrogen alongside other hormones like progesterone and testosterone can impact how estrogen acts in your body and how much of it you should have during different phases of life.

While estradiol rules your reproductive years, it should naturally drop after menopause. Women with higher estradiol in postmenopausal years appear to have an increased risk of breast cancer. This makes sense as our estrogen levels should naturally drop once we enter menopause.

But, due to lifestyle and environmental factors (as you'll learn about in more detail below), women in their 40s and 50s can experience estrogen dominance even after going through menopause. 

And while the risk of breast cancer tends to be higher for postmenopausal women, there’s some indication that high estrogen levels can increase the risk of breast cancer diagnosis even before menopause. It is challenging to study this for women who still get their periods, though, since estrogen levels fluctuate so much during the month, so the studies aren’t as reliable.

What About The Pill And Breast Cancer Risk?

You’re probably wondering, if increased exposure to estrogen can raise your risk for breast cancer, what about the pill? Is it a risk factor for breast cancer?

Studies are a bit mixed and therefore inconclusive, but not surprisingly, there does seem to be somewhat of an increased risk for breast cancer in women who use the pill. An early study that examined more than 50 studies on the pill found that women who were currently taking the pill, or even those that took the pill in the past ten years, had a slightly higher risk of breast cancer diagnosis. This risk returned to normal ten years after stopping oral contraceptives.

It may also be that once again, the balance of estrogen with other hormones like progesterone and testosterone is the real reason oral contraceptives might increase the risk. 

The bottom line is this: while we don't have a high-quality “smoking gun” study showing conclusively that birth control will increase your risk of breast cancer, the mixed results are still reason for caution.

Taking a synthetic hormone pill disrupts your body’s ability to regulate levels on its own, so it stands to reason that at least some of the time, for some women, using hormonal birth control could contribute to breast cancer risk.

Not all breast cancer is linked to estrogen, but estrogen receptor positive (ER+) cancers are  the most common type of breast cancer. And out of ER positive breast cancers, studies also show that around 65% of those cases also respond to progesterone. 

Estrogen receptor positive breast cancer means that estrogen encourages the growth of the cancer cells (as described above).  Part of the treatment plan for these types of cancers usually involves medications that lower estrogen levels in the body or help block the estrogen receptors (and progesterone, too, if needed). 

The connection between estrogen and breast cancer is clear, so optimal levels are vital. I wish I could tell you exactly what to do to avoid a breast cancer diagnosis altogether, but of course, I can’t — because it's an issue that's too complex to offer that type of advice. 

That said, there are things you can do to keep your estrogen in check:

Dr. Brighten's top tips on how women can keep estrogen in check for better health.

Remember that estrogen helps us feel healthy and sexy. The key is maintaining balance with other hormones. Here are my top lifestyle habits that promote healthy estrogen metabolism.

  • Maintain a healthy body weight. Remember that your fat tissue can make estrogen by converting androgens into estrogens. This means that as body fat increases, so does the amount of estrogen produced and circulated throughout your tissues.

Scientists estimatee that your risk for developing breast cancer jumps by 30% after menopause if your BMI is above 30. And being overweight appears to be linked to ER+ breast cancers, likely related to the increased estrogen production. While it’s much easier said than done to maintain body weight, the number one tip I advise for healthy weight is a healthy fiber intake. Try swapping your mindset from how many calories did I eat today to how much fiber from real, whole vibrant foods did I enjoy today?

  • Be mindful of alcohol intake. I know that a glass of wine can feel like a treat after a long day, but there are risks to that reward. Alcohol intake is closely linked to an increased risk of breast cancer (and overall hormone disruption), likely because it’s been shown to increase estrogen levels in the body. Alcohol is also linked explicitly to hormone-positive breast cancer. If you just love that drink, try to limit it to one daily or less and always enjoy your alcohol with food ladies!
  • Eat your leafy greens. Leafy greens, especially the brassicas like kale, broccoli, Brussels, and cabbage, are rich in sulfur-containing compounds that promote detoxification. These veggies may help to reduce breast cancer risk because they help your body eliminate excess estrogen. If you don’t love steamed veggies (I mean, does anyone?), try roasting them with sea salt, avocado oil and a little nutritional yeast for 30-40 minutes. The natural sweet and savory flavors will really stand out and you just might start craving veggies!
  • Use seeds for hormone-balancing superpowers. Seeds support a healthy hormone balance and appear to be protective against cancer. They are rich in minerals like zinc and magnesium, as well as fiber, which helps the body detoxify excess estrogens. You can try seed cycling to optimize your hormone balance throughout your menstrual cycle. I love putting some in smoothies, salads or even making power balls for a quick on-the-go afternoon snack or dessert.
  • Keep xenoestrogens out of your kitchen. Chemicals like BPA, phthalates, and BHT all mimic estrogen in the body. They sneak into our kitchen via canned goods, plastic containers, and other food storage items. 

Xenoestrogens are endocrine disruptors, meaning they mess with normal hormone balance and reproductive function, including estrogen balance. Aim for glass storage containers for your leftovers and use glass or stainless steel reusable water bottles instead of plastic. 

  • Bump up fiber for detoxification. Yep, back to fiber! Your digestive health is vital for overall health, especially hormone balance. The bacteria in your gut help regulate estrogenic activity in your body, so when your gut health is out of balance, so are your hormones.

Eating fiber feeds your gut bacteria and keeps them happy. It also keeps your bowels moving, so you remove extra estrogen from your body. Aim for 25-30 grams of fiber each day. Bonus points if you get a variety into your diet from the soluble, insoluble, resistant starches, prebiotic and probiotic sources too! Some of my favorites are artichokes, dandelion greens, kim chi, asparagus and black beans.

Estrogen Balance For Reduced Breast Cancer Risk

There’s a strong association between estrogen and breast cancer. While there are no guarantees when it comes to cancer, keeping your estrogen balanced through smart lifestyle changes like those I’ve listed above can reduce your risk and benefit your overall hormone health. 

If you're looking for a comprehensive approach that can help you achieve optimal hormonal balance, my free Hormone Starter Kit includes a 7 day meal plan, recipes, and other helpful info to get you on the right track. 

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References

  1. Key T, Appleby P, Barnes I, Reeves G. Endogenous sex hormones and breast cancer in postmenopausal women: reanalysis of nine prospective studies. J Natl Cancer Inst.. 2002. 94. 606-16.
  2. Travis RC, Key TJ. Oestrogen exposure and breast cancer risk. Breast Cancer Res.. 2003. 5. 239-247.
  3. Maynadier M, Nirdé P, Ramirez JM, et al.. Role of estrogens and their receptors in adhesion and invasiveness of breast cancer cells.. Adv Exp Med Biol.. 2008. 617. 485-491.
  4. Key TJ, Appleby PN, et al.. Sex hormones and risk of breast cancer in premenopausal women: a collaborative reanalysis of individual participant data from seven prospective studies.. Lancet Oncol.. 2013. 14. 1009-1019.
  5. Key TJ, Appleby PN, et al.. Circulating sex hormones and breast cancer risk factors in postmenopausal women: reanalysis of 13 studies.. Br J Cancer. 2011. 105. 709-722.
  6. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and hormonal contraceptives: collaborative reanalysis of individual data on 53 297 women with breast cancer and 100 239 women without breast cancer from 54 epidemiological studies.. Lancet. 1996. 347. 1713-1727.
  7. Lillie EO, Bernstein L, Ursin G.. The role of androgens and polymorphisms in the androgen receptor in the epidemiology of breast cancer.. Breast Cancer Res. 2003. 5. 164-173.
  8. Chan DSM, Abar L, Cariolou M, et al.. World Cancer Research Fund International: Continuous Update Project-systematic literature review and meta-analysis of observational cohort studies on physical activity, sedentary behavior, adiposity, and weight change and breast cancer risk. Cancer Causes Control.. 2019. 30. 1183-1200.
  9. Dorgan JF, Baer DJ, Albert PS, et al.. Serum hormones and the alcohol-breast cancer association in postmenopausal women.. J Natl Cancer Inst. 2001. 93. 710-715.
  10. Suzuki R, Orsini N, Mignone L, Saji S, Wolk A.. Alcohol intake and risk of breast cancer defined by estrogen and progesterone receptor status--a meta-analysis of epidemiological studies [published correction appears in Int J Cancer. 2008 Aug 15;123(4):981].. Int J Cancer.. 2008. 122. 1832-1841.
  11. Fowke JH, Longcope C, Hebert JR.. Brassica vegetable consumption shifts estrogen metabolism in healthy postmenopausal women.. Cancer Epidemiol Biomarkers Prev.. 2000. 9. 773-779.
  12. Velentzis LS, Cantwell MM, Cardwell C, Keshtgar MR, Leathem AJ, Woodside JV.. Lignans and breast cancer risk in pre- and post-menopausal women: meta-analyses of observational studies. Br J Cancer. 2009. 100. 1492-1498.
About The Author

Dr. Jolene Brighten

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Dr. Jolene Brighten, NMD, is a women’s hormone expert and prominent leader in women’s medicine. As a licensed naturopathic physician who is board certified in naturopathic endocrinology, she takes an integrative approach in her clinical practice. A fierce patient advocate and completely dedicated to uncovering the root cause of hormonal imbalances, Dr. Brighten empowers women worldwide to take control of their health and their hormones. She is the best selling author of Beyond the Pill and Healing Your Body Naturally After Childbirth. Dr. Brighten is an international speaker, clinical educator, medical advisor within the tech community, and considered a leading authority on women’s health. She is a member of the MindBodyGreen Collective and a faculty member for the American Academy of Anti Aging Medicine. Her work has been featured in the New York Post, Forbes, Cosmopolitan, Huffington Post, Bustle, The Guardian, Sports Illustrated, Elle, and ABC News. Read more about me here.