This story was produced in partnership with Vox as part of the discrimination issue of The Highlight.

Comedian Dulcé Sloan took to Twitter recently with a burning health question: “Soooo EVERY black woman has fibroids,” she wrote, injecting a bit of hyperbole, “and no one knows why?!” 

The tweet sparked a flurry of responses theorizing why 80% of Black women develop abnormal, noncancerous growths in their uteruses by age 50. Black women also experience fibroids at earlier ages than white women and with more severe symptoms, like pain and heavy bleeding. 

The responses ranged from well-researched hypotheses to wild speculations. Some pointed to relaxers and hair-care products. Others blamed birth control or childhood trauma. Diet came up frequently, with one person blaming coffee, specifically.

Ultimately, the string of comments only reinforced Sloan’s original post: No one knows why.

The lack of scientific consensus on what’s behind Black women’s severe rate of fibroids has led some to posit that it’s a result of “weathering”: the gradual whittling of Black people’s health due to the chronic stress of racial discrimination. But research on weathering is still developing, as is our knowledge of many of the potential explanations for the racial gap in fibroids.

Limited federal funding to support high-quality fibroid research, and the lack of Black biomedical researchers and clinicians, has left women with few answers. The consequences are great: 25% to 50% of women with fibroids get symptoms like anemia, heavy bleeding, and pain, according to the National Institutes of Health. They also may experience infertility and pregnancy complications at higher rates. 

Fibroids can be a particularly heavy burden for Black women, who are two to three times more likely to get a hysterectomy for treatment than other groups of women. 

Dr. Erica Marsh, chief of reproductive endocrinology and infertility at the University of Michigan’s Center for Reproductive Medicine, said her patients have proposed various reasons for their fibroids, including red meat, hair relaxers, and even “too many yams.” But it’s challenging to respond to their suspicions because, she said, “We don’t know.” 

Marsh co-authored a recent review of studies on the racial disparities of fibroids that determined that there’s not one factor that fuels Black women’s elevated rate of fibroids. Instead, they concluded that “as a result of the social, structural, and political context in the United States, Black women disproportionately experience a range of exposures across the life course that may contribute to their increased uterine fibroid incidence, prevalence, and severity.” Those exposures include excessive ambient pollution and hormone-disrupting chemicals, as well as elevated stress and nutritional deficiencies. 

The fibroid disparity is also linked to limited access to skilled gynecological doctors and racial bias in health care, the review stated. Black patients reported that their concerns were dismissed, leading to delays in diagnosis and suboptimal treatment by medical professionals.

Fibroids are a “multi-factorial condition,” said Brianna VanNoy, who studies environmental chemical exposures and reproductive health outcomes at Ohio State University College of Medicine, “not purely genetic, and not strictly environmental.” 

Much of the research on factors associated with fibroids does not confirm causation, or that these factors prompt fibroids to grow. Pinpointing how fibroids develop down to the cellular level would help women better manage factors that affect their risk and lead to better treatments, experts say. More research can help steer the conversation away from the tendency to blame fibroids on Black women’s behavior and put the focus on sustainable solutions.

Here’s an overview of what we know — and do not know — about what’s at the root of fibroids among Black women.

Chemicals

Research has suggested that Black women experience fibroids at increased rates due to exposure to harmful chemicals that disrupt human hormones. These toxins, called phthalates or “plasticizers,” are already associated with other reproductive issues like infertility and endometriosis.

Phthalates are found everywhere, from plastic food packaging and cosmetic products to medical devices like IV tubing and catheters. Hair relaxers also contain phthalates.

The chemicals can be inhaled or absorbed through the skin and mimic hormones. Some act like estrogen, which is responsible for cell growth and is known to stimulate fibroids. Fibroids appear in the uterus after hormone levels rise during puberty and usually shrink as those levels drop during menopause. 

Everyone is exposed to these hormone-mimicking chemicals daily, but Black women experience an elevated level of exposure, VanNoy said. A study published in 2020 that reviews national survey data A 2018 study of national survey data of over 38,000 female participants ages 1 to 85 years old (median age 26 years)  found that Black women had higher exposure to toxins like phthalates, pesticides, mercury, arsenic, and personal care and consumer product compounds.

Diet and vitamin D

A few epidemiological studies have found diet and certain nutrient deficiencies are linked to fibroid growth. A 2021 review of fibroid research found that low intake of fruit and green vegetables, lack of vitamin D, and pollutants ingested through food were associated with developing fibroids. Another study found that when women took vitamin D supplements, the size of their fibroids shrunk.

How specific food compounds lead to the onset of fibroids is unclear. But we do know that, for many Black women, access to fresh healthy foods is limited by structural racism. A legacy of white flight and disinvestment in low-income, urban areas has left 1 in 5 Black Americans living in a food desert — areas without grocery stores or with limited access to healthy food. 

We also know that Black people are significantly more likely than white Americans to be deficient in vitamin D, which is found in fish, egg yolk, and red meat. It’s also generated in our skin by sunlight, a process that can be impeded by melanin.

There’s evidence that vitamin D may obstruct how estrogen signals cell growth, helping reverse the development of fibroids.

Stress

Black women tend to experience higher levels of chronic stress than white women in the United States, which leads to higher cortisol levels, a hormone that — through a complex biological process — can influence the growth of uterine fibroids. 

There is limited research directly linking fibroids to stress, but some studies have shown a correlation. One found higher rates of fibroids in Black women who reported frequent experiences with racial discrimination. Another found that fibroids were more prevalent in Black women who reported high levels of stress over their lifetimes compared to those who reported no major high-stress life events. 

In Marsh’s 2019 review, she and her co-authors noted a study that found “Moderate daily stress and anger squelching” were linked to higher risk of fibroids among Black women.

It can be difficult to isolate stress as the dominant factor. A 2016 research review highlights the relationship between stress and fibroids, but also notes that stress from racial discrimination could prompt other fibroid-generating behaviors, such as heavy alcohol consumption and poor diet. 

Increasing the number of studies and quality of research on racial disparities in fibroids is necessary to make broad, societal changes, including reductions in the harmful chemicals allowed in our products, VanNoy said. Taking stock of toxic ingredients in everyday products isn’t feasible for many people.

In the meantime, women can be vigilant about their fibroid risk by assessing their health behaviors against suspected risk factors like diet and vitamin deficiency, and advocate for themselves when discussing health concerns with doctors. 

“None of us [environmental scientists] want the burden of these changes to fall on individual people, to fall on Black women,” VanNoy said.