What Is Aromatase And Why Inhibit It?


What Is Aromatase And Why Inhibit It?

One of the pages of my website that is visited a lot is 18 Natural Aromatase Inhibitors and I suspect the reason for this is that people with hormone-driven breast cancer, known as estrogen-receptor-positive (or ER+) breast cancer, are being prescribed drugs known as aromatase inhibitors. There is a lot of interest in using natural medicine and nutrients to do this job. So what is aromatase and why would we want to inhibit it?

What Is Aromatase?

Aromatase, also known as estrogen synthetase, is an enzyme that is responsible for the synthesis of the hormone estrogen in the body.  Aromatase plays a key role in the conversion of testosterone and androstenedione to various forms of estrogen (see diagram above). You can see that aromatase is required for the conversion to take place.  Aromatase is located in special cells in the ovaries, adrenal glands, testicles, placenta, fat cells and the brain.

Why Inhibit Aromatase?

In the search for drugs that will offer people the best chance of living without breast cancer recurrence, science offers us aromatase inhibitors (AIs).

Two approaches have been developed to reduce the growth-stimulatory effects of estrogen in ER+ breast cancer:

1.  Interfering with the ability of estrogen to bind to its receptor
2.  Decreasing circulating levels of estrogen

AIs are unable to stop ovaries from creating estrogen, however, so AIs are generally only offered to postmenopausal women.

Three Aromatase Inhibiting Drugs

There are currently three main aromatase inhibiting drugs:

letrozole – Femara, made by Novartis
anastrozole – Arimidex, made by Astra-Zeneca
exemestane – Aromasin, made by Pfizer

Exemestane (Aromasin) was approved by the United States Food & Drug Administration for those who have already been treated with tamoxifen.  The other two drugs, letrozole (Femara) and anastrozole (Arimidex), have been approved as either first-line treatment without prior use of  tamoxifen or for use following tamoxifen treatment.

The Problem Is… Those Awful Side Effects

As with many pharmaceutical drugs, there are side effects associated with taking AIs. Estrogen plays a huge part in a woman’s wellness and depriving our bodies of its effects can have some fairly serious complications.

In 2008, Breast Cancer Action, an education and advocacy organization dedicated to supporting people living with breast cancer, released a report entitled Side Effects Revisited: Women’s Experiences With Aromatase Inhibitors 1. BCA sent out a survey to 1,199 women taking aromatase inhibitors to discover what some of the side effects were and how debilitating they might be. See the results of the study at reference 1 below.  In particular see Table 3 on page 7.

The most common side effects  were pain, particularly joint pain, stiffness, and arthritis but other common side effects included hot flashes, bone pain, muscle pain, tiredness, insomnia, weight gain, loss of mental acuity, anxiety, depression and hair thinning. Only 2.3% of women reported they experienced NO side effects. If you are considering taking AIs, you owe it to yourself to read this report.

Estrogen is Important

Estrogen is a hormone we need in our bodies. Outside of its huge role in reproduction, estrogen also exerts major effects on the health of our bones. It works closely together with vitamin D and minerals to build and maintain our bones. All aromatase inhibitors moderately enhance bone loss. 2

Estrogen is also necessary for maintaining healthy cholesterol levels and offers protective benefits by increasing triglyceride concentrations in the bloodstream, which helps to guard against atherosclerosis.

Remember reading that some of the side effects of the AI drugs is loss of mental acuity? That’s because estrogen is very involved in brain health. It plays a role in memory retention, increasing serotonin levels, production of endorphins, and it even has a protective effect for nerves.

There are also estrogen receptors in the eyes, and vision changes are often one of the side effects people complain about after taking AIs.

Natural Medicine Approach

When we inhibit the biosynthesis of estrogen in every tissue of the body, no wonder the side effects are so life altering. Is it worth it? Are AIs really helping to keep recurrences at bay? Or are we suffering these side effects and still having recurrences?

Studies indicate that AIs are helping to keep recurrences at bay.  A 2005 study, Aromatase Inhibitors in the Treatment of Breast Cancer 3 indicates that the above three drugs are very effective, in vivo (meaning in the body) inhibition of whole-body aromatization ranged between 96.7% – 98.9%.  Most oncologists feel that AIs are the most effective hormonal therapy available for post-menopausal women.

But those side effects are very real and for many women, unendurable. These drugs are toxic to the body and could have repercussions down the line that we have no idea about because they have only been used since about 2000.

As a breast cancer coach, I can tell you that I am in contact with quite a few women who have taken these drugs and still suffered with recurrences and while I don’t possess statistical data, I can tell you that it does happen, all too frequently. No, it won’t happen for everyone, obviously, but I do believe there is a much better way to move forward.

Within the archives of this website you will no doubt read my words “it’s not all about estrogen” several times. What I mean by that is that having breast cancer, even ER+ breast cancer, is not all about having an overabundance of estrogen floating through our bodies. Cancer is a multi-factorial disease, with genetic, lifestyle and environmental factors interacting to create the havoc that cancer can be.

Natural medicine offers other ways of dealing with this problem, for instance:
1.  Looking into why estrogen levels are high in the first place and then managing that. Is it the body’s own estrogen, or is it an overabundance of xenoestrogens?
2. What is the patient’s diet like?
3.  What factors in the patient’s life may have contributed to the development of breast cancer?
4. What kind of stress was the patient under prior to diagnosis?
5.  What is the status of the patient’s immune system? What can we do to support it?
6.  What therapies has the patient already undergone to address the cancer? (Knowing this helps to establish the level of toxicity present.)
7.  What natural foods and supplements can assist the patient with blocking aromatase if that proves necessary?

These are just some of the questions a natural medicine practitioner will ask, looking at the patient as a whole and not just treating one small aspect of the disease.

1. Side Effects Revisited: Women’s Experiences With Aromatase Inhibitors –http://bcaction.org/wp-content/uploads/2011/03/AI-Report-June-2008-Final-ONLINE.pdf

2. The potency and clinical efficacy of aromatase inhibitors across the breast cancer continuum – http://annonc.oxfordjournals.org/content/early/2010/07/08/annonc.mdq337.full

3. Aromatase Inhibitors in the Treatment of Breast Cancer – http://citeseerx.ist.psu.edu/viewdoc/download?doi=

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4 thoughts on “What Is Aromatase And Why Inhibit It?

  1. Marnie, I have a question. If these unpleasant side effects are a result of the low amounts of estrogen in the body, what difference does it make if you lowered the estrogen through a pill or a food or other natural product? The result is the same – less estrogen in the body – a good thing in terms of containing the cancer – but with all the difficulties that result from the reduced estrogen. Whatever the path to achieving it – whether chemically or ‘naturally’ – you still end up with less estrogen and the side effects that are a result of having less estrogen. ‘Natural’ products also contain chemicals – it’s the chemistry that makes them effective.

    1. Hi Tereze.
      Thanks for your question and I apologize for taking so long to answer it. I’ve been away on a family emergency. I’ll do my best to answer your question. The unpleasant side effects of pharmaceutical aromatase inhibitors are not generally encountered with natural aromatase inhibitors. While it’s true that natural products also contain chemicals, the natural ones are more easily metabolized by the body. For instance, plant estrogens (phytoestrogens) bind to estrogen receptors and are biochemically much weaker than the body’s own estrogen. While estrogen can stimulate the growth of both ovarian and breast cancer, weaker phytoestrogens bind to the receptors and lock out the more powerful estrogens that can encourage disease – without the nasty side effects encountered by pharmaceutical hormone blockers. I hope this helps to answer your question and again, I apologize for the delay.
      Warmest regards,

  2. Dear Marnie,

    I am 42 years old and was diagnosed to have stage 2B breast Mucinous Carcinoma last year. I am both ER & PR positive but Her2 negative. I started taking tamoxifen last December 11, 2015/immediately after my radiation therapy. However, after 4months of taking tamoxifen, I started to feel several discomforts such as random fatigue & upper back aches. My memory is somehow affected.
    For a year now, I have been taking 4Life Transfer Factor plus and this supplement helps me in maintaining a good immune system. They have a targeted product called Belle Vie which was formulated to protect breast from cancer. One primary composition of Belle Vie is phytoestrogens. May I know if you have patients who tried this supplement as a natural alternative of aromatase inhibitor drugs?
    I am looking for best alternative for tamoxifen without sacrificing it’s benefits thus improving my quality of life.

    Thank you and I hope you can help me with my dilemma.
    Best regards

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