What Causes Fibroids?
Why This Matters
If you've recently been told you have fibroids, one of your first questions is likely to be, "Why did this happen to me?"
Many women worry that they've done something wrong. They wonder whether their diet caused the fibroids, whether stress is to blame, or if there was something they could have done to prevent them.
The truth is that fibroids are extremely common, and in most cases there is nothing you did to cause them.
Although researchers have learnt a great deal about fibroids over the past few decades, we still don't know exactly why one woman develops fibroids while another doesn't. We do know, however, that several factors can increase the likelihood of developing them.
Understanding these factors can help separate fact from myth and may help you make informed decisions about your health.
Quick Summary
The exact cause of fibroids is still unknown.
Fibroids develop from a single muscle cell in the wall of the uterus that begins to grow abnormally.
Oestrogen and progesterone encourage fibroid growth.
Genetics play an important role.
Family history increases your risk.
Fibroids are more common between the ages of 30 and 50.
Black women are more likely to develop fibroids and often at a younger age.
Lifestyle factors such as obesity and vitamin D deficiency may influence risk, but they do not directly cause fibroids.
There is currently no guaranteed way to prevent fibroids.
What Do We Know About the Cause?
Fibroids (also called uterine leiomyomas) begin when a single smooth muscle cell in the wall of the uterus develops changes that allow it to multiply more than it should.
Instead of stopping when it reaches its normal size, the cells continue dividing, gradually forming a firm lump made up of muscle cells and fibrous connective tissue.
Researchers believe that this process occurs because of a combination of:
hormones
genetic changes within the fibroid cells
growth factors
inherited susceptibility
environmental influences
Rather than having one single cause, fibroids appear to develop when several factors come together.
The Role of Hormones
Hormones are one of the biggest influences on fibroid growth.
The two main hormones involved are:
Oestrogen
Progesterone
These hormones naturally rise and fall throughout a woman's reproductive years.
Fibroids contain more hormone receptors than normal uterine muscle, making them especially sensitive to these hormones.
As a result:
Fibroids often grow during the reproductive years.
They may enlarge during pregnancy because hormone levels are high.
They usually shrink after the menopause when hormone levels decline.
It's important to understand that hormones encourage fibroids to grow. They are not necessarily the original cause.
Genetics
Genetics plays a significant role.
Many fibroids contain small genetic changes that are not present in the rest of the body. These changes occur only within the fibroid itself and help explain why the cells continue growing.
Researchers have identified several genes associated with fibroid development, including changes affecting genes involved in cell growth and hormone signalling.
Having these genetic changes does not mean fibroids are inherited directly, but they help explain why some women are more susceptible than others.
Family History
Fibroids often run in families.
If your mother or sister has fibroids, your own risk is increased.
This does not mean you will definitely develop them, but it suggests that inherited genes contribute to your overall risk.
Age
Fibroids are uncommon before puberty because hormone levels are low.
They become increasingly common during the reproductive years, particularly between the ages of 30 and 50.
After menopause, most fibroids stop growing and many gradually shrink.
Ethnicity
Research consistently shows that fibroids are more common in women of African or Caribbean ancestry.
Compared with women from many other ethnic backgrounds, Black women are more likely to:
develop fibroids at a younger age
have larger fibroids
develop multiple fibroids
experience more severe symptoms
Researchers believe this is likely due to a combination of genetic and environmental factors, although the exact reasons remain unclear.
Weight and Lifestyle
Being overweight or obese has been linked with a higher risk of fibroids.
One possible explanation is that body fat produces additional oestrogen, which may encourage fibroid growth.
Other lifestyle factors have also been studied, including:
physical activity
diet
alcohol
smoking
Some studies suggest these factors may influence risk, but none has been shown to directly cause fibroids.
Researchers continue to investigate how lifestyle affects fibroid development.
Vitamin D
Vitamin D has become an area of growing research.
Several studies have found that women with lower vitamin D levels appear more likely to develop fibroids.
Laboratory studies also suggest vitamin D may slow fibroid cell growth.
However, researchers do not yet have enough evidence to recommend vitamin D supplements specifically to prevent or treat fibroids unless you are deficient. More research is needed.
Pregnancy
Pregnancy does not cause fibroids.
However, because hormone levels rise significantly during pregnancy, existing fibroids may increase in size, particularly during the first half of pregnancy.
Many shrink again after the baby is born.
Can Stress Cause Fibroids?
Stress is often blamed for many health conditions, and some women wonder whether it caused their fibroids.
At present, there is no strong evidence that stress directly causes fibroids.
Living with fibroids can certainly be stressful, especially if they cause heavy bleeding, pain or fertility problems, but stress itself has not been proven to be the underlying cause.
Can Fibroids Be Prevented?
Unfortunately, there is currently no guaranteed way to prevent fibroids.
Maintaining a healthy weight, exercising regularly, eating a balanced diet and treating vitamin D deficiency may support overall health, but they cannot guarantee that fibroids will not develop.
Researchers continue to study whether lifestyle changes can reduce risk, but more evidence is needed.
What Does This Mean for You?
Learning that you have fibroids can leave you searching for a reason.
The most important thing to remember is that fibroids are incredibly common, and in most cases they are not the result of anything you did or failed to do.
They develop because of a complex combination of hormones, genetics and biological processes that researchers are still working to fully understand.
While some lifestyle factors may influence risk, there is currently no proven way to completely prevent fibroids.
Understanding what we know—and what we still don't know—can help you focus on the things you can control, such as learning about your treatment options, maintaining your overall health and working with your healthcare team to manage any symptoms.
Key Takeaways
The exact cause of fibroids remains unknown.
Hormones encourage fibroid growth but are unlikely to be the sole cause.
Genetics and family history play an important role.
Fibroids are most common during the reproductive years.
Black women have a higher risk of developing fibroids.
Lifestyle factors may influence risk but do not directly cause fibroids.
There is currently no guaranteed way to prevent fibroids.
Most women develop fibroids through factors beyond their control.
Frequently Asked Questions
Did I do something to cause my fibroids?
Almost certainly not. Fibroids develop because of complex biological processes that are largely outside your control.
Can diet make fibroids disappear?
There is currently no scientific evidence that any specific diet can eliminate fibroids, although a healthy diet supports overall wellbeing. Research into nutrition and fibroids is ongoing.
Will my fibroids keep growing forever?
Usually not. Fibroids often grow during the reproductive years but tend to shrink after menopause as hormone levels fall.
If my mum had fibroids, will I get them too?
Not necessarily. A family history increases your risk but does not guarantee that you will develop fibroids.
Can I stop fibroids from developing?
There is no proven way to completely prevent fibroids, although maintaining a healthy lifestyle is beneficial for your general health.
References
National Institute for Health and Care Excellence (NICE). Heavy menstrual bleeding: assessment and management (NG88).
Royal College of Obstetricians and Gynaecologists (RCOG). Information for You: Fibroids.
American College of Obstetricians and Gynecologists (ACOG). Uterine Fibroids.
Stewart EA, et al. Uterine Fibroids. Nature Reviews Disease Primers.
Bulun SE. Uterine Fibroids. New England Journal of Medicine.
World Health Organization (WHO). Women's reproductive health resources.