Vitamin D and Fibroids: What do we really know?

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Should I be taking Vitamin D for Fibroids?

If you have fibroids, you may have been told that vitamin D can stop them growing or even shrink them. You may also have been told to buy a supplement, with no clear advice on the type, dose or need for a blood test. I found this confusing, so we did some digging and here's what we found.

Research does show a link between low vitamin D levels and fibroids. A few small trials have also tested vitamin D supplements in women with fibroids. The results are worth knowing about, but they do not prove that vitamin D treats or prevents fibroids.

This guide explains what the studies found, the doses they used, what a vitamin D blood test can tell you, and how to avoid taking too much.

What the science says, at a glance

Vitamin D is one of the most researched nutrients linked to fibroid risk and progression. While it is not a cure, clinical studies suggest it may play a supportive role, particularly for women who are deficient.

Research into vitamin D and fibroids is promising but still emerging. Peer reviewed statically significant studies have proven a link between Vitamin D deficiency and Fibroids. However, only a handful of studies with small cohorts (100 participants or less) have show that taking Vitamin D supplements can slow or stop Fibroid growth.

There is no clinically founded evidence to support any claims that taking Vitamin D can shrink Fibroids.

What vitamin D can and can’t do

Evidence suggests it may support

✔️ Slowing or preventing fibroid growth in some women

✔️ Supporting normal hormone signalling

✔️ Addressing a common nutritional deficiency (especially in the UK)

What it does not reliably do

❌ Consistently shrink large fibroids

❌ Replace medical or surgical treatment

❌ Guarantee symptom improvement (e.g. bleeding or pain)

Vitamin D should be viewed as foundational, long-term nutritional support, not a standalone treatment. The NHS and NICE do not recommend or prescribe vitamin D as treatment for Fibroids.

What is Vitamin D and why is it important?

The body makes vitamin D when sunlight reaches the skin. We also get small amounts from foods such as oily fish, egg yolks and fortified foods. In the UK, sunlight is often too weak for the body to make enough vitamin D during autumn and winter which is why so many people are deficient.

Vitamin D helps the body keep bones, teeth and muscles healthy. It also has a role in normal immune function and cell division.

Vitamin D helps your body absorb calcium and phosphate, which are essential for healthy bones, muscles and nerves. Magnesium also plays an important role because it's needed to activate vitamin D and allow it to work properly.

Although we often think of vitamin D as a vitamin, it also behaves like a hormone. Your body can make it from sunlight, and once it's activated, it travels around the body carrying messages to many different tissues, including the bones, immune system and reproductive organs. It helps to regulate cell growth, inflammation and hormone signalling. Researchers believe all of these processes may play a role in how fibroids develop and grow.

Why are researchers studying vitamin D and fibroids?

Fibroids are non-cancerous growths made from muscle and fibrous tissue in or around the womb. Researchers have found vitamin D receptors in fibroid cells. Receptors are tiny parts of a cell that receive messages from hormones, vitamins and other substances. They help tell the cell how to respond.

In lab studies, active forms of vitamin D have affected fibroid cell growth, inflammation and the build-up of fibrous tissue. This gives scientists a reason to study vitamin D in women. But a result in cells or animals does not prove that a supplement will improve symptoms or shrink fibroids in real life.

What do studies in women show?

Low vitamin D is linked with fibroids

Observational studies compare people without changing their treatment. Many have found lower vitamin D levels in women with fibroids. Some also found that lower levels were linked with larger fibroid volume.

A US study led by Donna Baird found that women with sufficient vitamin D were less likely to have fibroids than women with lower levels. Another study found an inverse link between vitamin D level and fibroid volume across ethnic groups. These findings are useful, but they cannot show cause and effect. Weight, sun exposure, diet, skin tone, age and other factors may affect both vitamin D status and fibroid risk.

Trials of vitamin D supplements

Clinical trials give stronger evidence because researchers test an intervention. So far, most vitamin D and fibroid trials have been small, short and limited to women with low vitamin D.

Ciavattini, 2016

A small trial of 108 women with low levels of vitamin D were given a personalised dose of D3 based on their level of deficiency, for 12 months. Women who took the vitamin D treatment were less likely to develop larger, more numerous or more extensive fibroids during the study period than women who did not receive treatment. But the trial was not randomised, had a small sample size, didn't use a standard D3 supplement and mostly looked at fibroid progression, not improvements in symptoms such as heavy bleeding.

Hajhashemi, 2019, and Arjeh, 2020

69 women with vitamin D deficiency were given 50,000 IU D3 every 2 weeks, for a 10 week period. Hajjhashemi found the average fibroid size was lower in the vitamin D group than the placebo group. While Arjey found fibroid volume did not fall by a clear amount in the treatment group, but it rose in the control group. Long-term effects were unknown. Both trials were very small and very short.

Suneja, 2021

Over 16 weeks, women with low vitamin D were given 60,000 IU weekly for 8 weeks, then every 2 weeks for 8 weeks. They found symptoms and fibroid measures improved or stabilised. Again the study was small and needs confirmation in larger controlled trials.

Tanha, 2021

204 women with fibroids and vitamin D insufficiency were given 50,000 IU weekly for 2 months. The study reported less fibroid overgrowth in the treatment group., but the follow-up was short.

Tabrizian, 2021

A small clinical trial comparing two groups over 12 weeks; 50,000 IU weekly in one group, with a lower-dose comparison group. The study did not show a clear short-term reduction in fibroid size.

In 2024 a systematic review and meta-analysis combined available trials. It found a small difference in fibroid size change in favour of vitamin D, but the studies were very different from each other. Their doses ranged from 50,000 IU weekly to 50,000 IU every two weeks, and treatment lasted about two to six months. This high level of variation lowers confidence in a single overall result.

The clearest conclusion is that vitamin D is promising enough for more research. It is not yet proven as a fibroid treatment. We also do not know if the same results would apply to women whose vitamin D level is already healthy.

How can you tell if you are deficient?

The only reliable way to know is with a blood test called a 25-hydroxyvitamin D (25(OH)D) test. This measures the amount of vitamin D circulating in your blood. This can help a GP or other qualified clinician choose a plan that matches your needs instead of guessing from the strength on a pharmacy shelf.

In the UK, a reading below 25 nmol/L is considered deficient, while 25-50 nmol/L is insufficient for some people. Levels are improving but may still be below what's considered adequate for optimal musculoskeletal health. Your healthcare professional may recommend supplementation depending on your individual circumstances. Above 50 nmol/L is sufficient.

A result should be read with your health history. Different services may use slightly different cut-offs. Your clinician may also consider your calcium level, kidney health, medicines, pregnancy status, symptoms and risk factors.

Testing is most useful when the result will change what you do. A test does not tell you whether vitamin D caused your fibroids, and it cannot predict whether a supplement will change their size.

Who is more at risk of low vitamin D?

You may be more likely to have low vitamin D if you have darker skin, cover most of your skin outdoors, spend little time outside, are pregnant, are older, have a higher body weight, or have a condition that affects how your gut absorbs nutrients.

This matters for health equity. Black women are more likely to develop fibroids, often at a younger age, and may have larger or more numerous fibroids. People with darker skin living in the UK are also at higher risk of low vitamin D because melanin reduces the amount made from sunlight. Researchers are studying whether vitamin D is one part of this gap, but it cannot explain the full difference. Genetics, environment, stress, income and unequal access to care may all play a role.

Can you take too much vitamin D?

Yes. Vitamin D is stored in the body. Taking too much over time can cause calcium to build up in the blood. This is called hypercalcaemia. It can weaken bones and damage the kidneys and heart.

For most adults, the NHS says not to take more than 100 micrograms, or 4,000 IU, a day unless a clinician has told you to. Count vitamin D from every supplement you use, including multivitamins, sprays and combination products.

Possible signs of too much vitamin D or high calcium include feeling sick, vomiting, constipation, unusual thirst, passing urine often, weakness, confusion or kidney stones. Stop taking the supplement and seek medical advice if you are worried about these symptoms.

The right type of vitamin D for Fibroids

If you’re looking for Vitamin D supplements, it’s important to get your bloods tested first and check the label for both micrograms and IU. Ten micrograms equals 400 IU.

Take the dose advised for you. Do not copy a study dose from the internet.

Types of Vitamin D

Vitamin D1 (calciferol) is found in fish oils.
Vitamin D2 (ergocalciferol) is found in plants.
Vitamin D3 (cholecalciferol) is produced by the body when UV light from the sun interacts with cholesterol in the skin.

The most active form of vitamin D is called 25-hydroxyvitamin D3. It has activity in almost every tissue of our bodies.

Vitamin D3 (cholecalciferol) is the form used in most fibroid-related studies and is more effective than vitamin D2 at raising and maintaining blood vitamin D levels.

What to avoid

Vitamin D1 (calciferol) or D2 (ergocalciferol)
Very low-dose supplements (e.g. 400 IU only)

What dosage should I look for?

Please consult your GP and request blood tests before making any changes to your diet.

Do not take more than 100 micrograms (4,000 IU) of vitamin D a day unless a medical professional has instructed you to, as it could be harmful. This applies to all adults (including pregnant and breastfeeding women) and children aged 11 to 17 years.

Vitamin D is best absorbed when taken with food containing fat. Some people also take vitamin D alongside magnesium and vitamin K2, which support vitamin D metabolism and calcium balance, though these have not been studied specifically for fibroid outcomes.

When should I take it?

There isn’t much in the way of studies in regards to time of day, but taking vitamin D with a meal, ideally rich in fats will increase absorption.

The Leio Take

Vitamin D deserves attention, but not hype. Women with fibroids often have lower vitamin D levels, and a 2024 pooled analysis of five small trials found a reduction in fibroid size in favour of supplementation. The trials were short and varied in quality, dose and design. This means we still cannot say how much benefit a woman is likely to get, whether symptoms improve, or whether the findings apply when vitamin D levels are already adequate.

The practical next step is to understand your own vitamin D level and risk. If you are deficient, ask what dose is meant to correct it, how long to take it, and when to check again. That is more useful than choosing a product by strength alone.

Medical Disclaimer - This article is for education only and does not replace personal medical advice. Supplements are not suitable for everyone and may interact with health conditions or medicines. Speak to your GP, pharmacist or specialist before starting a high-dose supplement, changing prescribed treatment or making decisions about fibroid care.

Warning - Taking too many vitamin D supplements over a long period of time can cause too much calcium to build up in the body (hypercalcaemia). This can weaken the bones and damage the kidneys and the heart. NHS

Consult your GP and request blood tests before making any changes to your diet.