The exact cause of fibroids is not well understood, however it is known that the growth of fibroids is stimulated by the hormone oestrogen. Fibroid cells are often genetically different from normal uterine cells, so it's likely that genetic mutation is another factor that triggers fibroid development.
There are several known risk factors that increase a woman's risk of developing one or more fibroids. The different risk factors for fibroids include things like hormone levels, family history, and lifestyle factors.
It is well established that the growth of fibroids is dependent on oestrogen, although it's not known exactly how this hormone triggers fibroid development. Because fibroid growth is triggered by oestrogen, women who have high levels of this hormone—or an excess of oestrogen in comparison to the hormone progesterone—have an increased risk of developing fibroids.
Many women who have fibroids during their reproductive years find that the fibroids shrink after they reach menopause. This is because the ovaries stop producing oestrogen, which means there is considerably less of the hormone circulating. Similarly, when a woman has fibroids they are likely to increase in size if she becomes pregnant, because oestrogen production increases during pregnancy.
Oestrogen is produced in the ovaries and in certain other organs such as the breasts. It's also produced by fat cells. Because of this, women who are overweight or obese produce more oestrogen, and therefore have a higher risk of developing fibroids.
There is some evidence to suggest that a diet high in red meat and processed meat products such as ham can increase the risk of developing fibroids. Other dietary risk factors include vitamin D deficiency and alcohol consumption.
There is also evidence that a diet high in green vegetables helps to protect against fibroid development.
If you have a close family member with fibroids, there's a much greater risk that you'll develop them too. In particular, your risk of having fibroids is around three times higher than normal if your mother has fibroids. This is likely to be because the amount of oestrogen the body produces is partly an inherited trait.
Ethnic origin can play a role, too. Women of African-American and African-Caribbean descent have a higher risk of fibroids than other women. There are no other known ethnicity risk factors that increase a woman's risk of having fibroids.
Interactions between Different Risk Factors
When more than one risk factor is present, they can greatly increase the likelihood that a woman will develop fibroids. For example, if a woman is overweight and has a family history of fibroids, she's much more likely to develop fibroids than if she was only affected by one of those risk factors.
Because some risk factors can't be controlled—such as ethnicity and family history—when those risk factors are present it's important to focus on the factors that can be controlled. For example, if you have a family history of fibroids, then limiting red meat, eating more green vegetables, or managing your weight, may help to mitigate your risk of developing fibroids.