What Causes Fibroids?

So, the real question is, what causes fibroids?

This is the never-ending question (or debate). Some people claim it is one thing or the other, but the truth is, there are a bunch of factors.

Here’s what we *do* know, and how we ultimately can learn to support our body in a way that leads to the diminished likelihood or continued growth of fibroids.

Big Factors

reasons for fibroids

Estrogen excess (or dominance). We do know this is a huge factor when it comes to fibroids. When there’s too much estrogen circulating in our body without enough progesterone to balance it out, or our body favors the 4-OH or 16-OH pathways in metabolizing estrogen, it is a feeding ground for fibroids.

Excess estrogen has a lot of factors at play, from perimenopause to xenoestrogens to thyroid and adrenal issues. What makes the situation tough, though, is this fibroids have can have progesterone receptors alongside estrogen receptors (in some cases, progesterone blockers known as SPRMs have been used to reduce fibroids). So it’s not always clean-cut.

Liver issues. This is a huge factor, which connects directly to excess estrogen. How your liver is metabolizing (or “detoxing”) estrogen is just as – or maybe more – important than estrogen in and of itself.

Our liver oversees 750 processes in our body, and unfortunately, metabolizing estrogen can get pushed to the back of the line, particularly when it needs to focus on things like alcohol, caffeine, drugs, and pesticides first.

There are also genetic propensities to impaired detoxification. I talk more about this below.

Liver support is essential when you have fibroids, and I’ll talk more about this is in an upcoming post.

Adrenal dysfunction. The often overlooked adrenals are also a big part of the picture. Stress triggers cortisol output, which can negatively impact progesterone levels, once again allowing for estrogen to go unchecked which feeds fibroid growth.

Thyroid Disorders. Studies have shown an association between a low functioning thyroid and an increased risk of fibroids. Here are a few studies:

Relationship between thyroid disorders and uterine fibroids among reproductive-age women

Overt hypothyroidism is associated with the presence of uterine leiomyoma: a retrospective analysis

Uterine Fibroids Increase the Risk of Thyroid Cancer

Low Vitamin D. There are quite a few studies that connect low vitamin D levels with fibroids, including this one and this one.


Gene variations. Several genes play a part of the processing, or metabolization, of estrogen. That’s a fancy way of saying after your body uses estrogen, your liver breaks it down to help remove it from your body so that it doesn’t cause issues like fibroids and caner. So if you have genes that have what are called “variations” or “mutations” on them, your body may be slower in processing estrogen, which can lead to higher levels.

Some of the more well-known genes that impact estrogen metabolism include CYP450, COMT, and UGT. CYP450 enzymes play major roles in Phase 1 estrogen metabolism in the liver, which is the first phase of detoxifcation. COMT and UGT work in Phase 2, which is the second phase of detoxification, where the toxin from Phase 1 is made water-soluble and no longer a threat. 

I’ll do a longer post on this process of estrogen detoxification, but for now, know that if your CYP450 aren’t up to perfect working order, that can mean estrogen may favor the 4-OH or 16-OH pathways, both of which are associated with fibroid growth. If COMT and UGT aren’t fully functioning, the process of detoxificaiton can get backed up, maintaining higher and more threatening levels of estrogen.

Understanding your unique genetic code can guide you to what specific nutrients your body needs to fend off fibroid growth. That’s why I recently started utilizing 3×4 genetic testing with my clients.

Xenoestrogens. Xenoestrogens also play a role in fibroid growth, as these are chemicals that act as estrogen in the body. They will actually lock into your estrogen receptors, taking the place of your own estrogen! Unfortunately, they are tougher for the body to detoxify and move out, and are often stored in our tissues.

One of the most important things to do to combat xenoestrogens is to pay attention to the amount of chemicals in your life and environment. Remove as much plastic from your day-to-day as you can (don’t drink or eat out of plastic!), change your hair, face, and body care products to non-toxic options, drink reverse osmosis (with minerals added) or distilled water, and purchase house-cleaning products that are chemical-free.

I’ll cover physical detox supports that help move out xenoestrogens in another post. In the meantime, check out my interview with Environmental Toxins Expert Lara Adler, Environmental Toxins Can Wreck Your Hormones & What You Can Do About It.


Pulling It All Together

These are some of the factors the influence fibroid growth, but there are many more issues at play, including emotiona and spiritual reasons.

I dive into these and a whole lot more in my Fibroids 101 course. Get 20% off the course with code “byefibroids” at checkout.


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