What Causes Uterine Fibroids?
The exact cause of uterine fibroids is not fully understood, but they are thought to develop from a combination of hormonal, genetic, and environmental factors. Oestrogen and progesterone — the hormones that stimulate the uterine lining — appear to promote fibroid growth.
Hormonal Factors
Oestrogen and progesterone are the two hormones that regulate the menstrual cycle and stimulate the growth of the uterine lining (endometrium) each month. These same hormones are known to promote the growth of fibroids. Fibroid tissue contains a higher concentration of oestrogen and progesterone receptors than normal uterine muscle, making fibroids particularly sensitive to hormonal stimulation.
This hormonal link explains why fibroids typically develop during the reproductive years, when oestrogen and progesterone levels are at their highest, and why they tend to shrink after the menopause, when hormone levels decline. It also explains why certain hormonal treatments, such as GnRH agonists, can temporarily reduce fibroid size by suppressing oestrogen production.
Conditions that expose the body to higher or prolonged levels of oestrogen — such as early onset of menstruation (before age 10), obesity, and never having been pregnant — are associated with an increased risk of fibroid development.
Genetic Factors
Research has demonstrated a clear genetic component to fibroid development. Studies of families and twins show that women whose mothers or sisters have had fibroids are significantly more likely to develop them. The risk increases further if a woman has multiple first-degree relatives with the condition.
At the cellular level, researchers have identified specific genetic mutations that are commonly found in fibroid cells. Mutations in the MED12 gene are present in approximately 70% of fibroids, while other fibroids harbour alterations in genes such as HMGA2 and FH. These mutations are believed to cause normal uterine muscle cells to grow abnormally, forming fibroid tumours.
Ongoing genomic research continues to improve our understanding of the genetic basis of fibroids, which may eventually lead to more targeted prevention and treatment strategies.
Race and Ethnicity
Epidemiological studies consistently show that Black women are disproportionately affected by uterine fibroids. Black women are two to three times more likely to develop fibroids than white women, tend to develop them at a younger age, and are more likely to have larger and more numerous fibroids that cause symptoms.
The reasons for this disparity are not fully understood and are likely multifactorial. Genetic differences, higher rates of vitamin D deficiency, differences in oestrogen metabolism, and socioeconomic factors that affect access to healthcare may all contribute. Importantly, awareness of this increased risk allows for earlier screening and intervention when appropriate.
At the North London Fibroid Clinic, we are committed to providing equitable, culturally sensitive care and ensuring that all women have access to the information and treatment options they need, regardless of their background.
Age
The risk of developing fibroids increases with age, peaking during the late reproductive years. Fibroids are most commonly diagnosed in women between the ages of 30 and 50. Before puberty, fibroids are virtually nonexistent, and after the menopause, existing fibroids typically shrink as oestrogen and progesterone levels fall.
However, women who take hormone replacement therapy (HRT) after the menopause may find that their fibroids do not shrink as expected or may even continue to grow, as HRT provides a continued source of oestrogen and progesterone. Women with known fibroids should discuss the potential implications of HRT with their doctor.
Family History
Having a first-degree relative (mother or sister) with fibroids increases your risk of developing them by approximately two to three times. If both your mother and sister have had fibroids, your risk is even higher. This strong familial association underlines the genetic contribution to fibroid development.
If you have a family history of fibroids and are experiencing symptoms such as heavy periods, pelvic pain, or urinary frequency, it is worth discussing these with your GP or a specialist. Early identification can lead to timely management and a better outcome.
Lifestyle Factors
Several modifiable lifestyle factors have been associated with an increased risk of fibroid development. Obesity is one of the most consistently identified risk factors, with overweight and obese women having a 20–50% higher risk than women of a healthy weight. Fat tissue produces oestrogen, and higher body fat levels can increase circulating oestrogen, which may stimulate fibroid growth.
Dietary patterns may also play a role. Diets high in red meat and low in fruit, vegetables, and dairy products have been associated with an increased risk of fibroids in some studies. Conversely, diets rich in green vegetables, fruit, and dairy have been associated with a reduced risk.
Vitamin D deficiency has emerged as a potentially important risk factor. Several studies have found lower vitamin D levels in women with fibroids compared to those without, and laboratory research suggests that vitamin D may inhibit fibroid cell growth. Alcohol consumption, particularly beer, has also been linked to an increased risk in some epidemiological studies.
Can Fibroids Be Prevented?
There is currently no proven way to prevent uterine fibroids from developing. However, certain lifestyle choices may help reduce your risk or slow fibroid growth. Maintaining a healthy weight, eating a balanced diet rich in fruits, vegetables, and whole grains, exercising regularly, and ensuring adequate vitamin D intake are all measures that may be beneficial.
Regular gynaecological check-ups can also help with early detection. If fibroids are identified at an early stage, they can be monitored and treated promptly if they begin to cause symptoms. Women with known risk factors, particularly a family history of fibroids, should be vigilant about any changes in their menstrual pattern or the development of pelvic symptoms.
If you have concerns about your risk of developing fibroids or would like to discuss preventive strategies, book a consultation with our team.
Frequently Asked Questions
References
- NHS — Fibroids: Causes. Available at: https://www.nhs.uk/conditions/fibroids/causes/
- NICE Clinical Knowledge Summaries — Fibroids: Risk Factors. Available at: https://cks.nice.org.uk/topics/fibroids/
- Baird DD, Dunson DB, Hill MC, Cousins D, Schectman JM. High cumulative incidence of uterine leiomyoma in black and white women. American Journal of Obstetrics and Gynecology. 2003;188(1):100–107.
- Sabry M, Halder SK, Allah AS, et al. Serum vitamin D3 level inversely correlates with uterine fibroid volume. Fertility and Sterility. 2013;99(5):1314–1319.
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