Millions of women with uterine fibroids share one thing in common besides the tumors themselves: low vitamin D levels show up again and again in the research.
Quick Take
- A National Institutes of Health study found women with enough vitamin D were 32% less likely to develop fibroids.
- A 2022 review of 14 studies found every single one linked low vitamin D to more fibroids.
- Lab research on rats showed vitamin D shrank fibroid tumors by about 75%.
- Human trials show slower fibroid growth with vitamin D, but shrinking existing fibroids is a tougher, less proven claim.
What The Original NIH Study Found
The finding traces back to a National Institute of Environmental Health Sciences study that tracked 1,036 women between ages 35 and 49. Researchers used ultrasounds to confirm fibroids and blood tests to measure vitamin D. Women with sufficient vitamin D levels were 32% less likely to have fibroids than women who fell short.
The study also uncovered a striking racial gap. Only 10% of Black women in the study had sufficient vitamin D, compared to 50% of white women. Fibroids are already known to hit Black women harder and earlier. That overlap makes vitamin D deficiency a factor worth taking seriously, not a side note.
The Pattern Holds Up Across Dozens Of Studies
One study rarely settles anything in medicine, so researchers went looking for more proof. A 2022 systematic review pulled together 14 separate clinical studies covering 3,535 women. Every single one found the same inverse relationship: less vitamin D, more fibroids.
That same review looked at treatment, not just risk. Five studies tested giving women vitamin D directly. Four of the five showed it slowed fibroid growth. One pilot study even found women who took vitamin D after fibroid removal had smaller regrowth than those who didn’t.
A 2024 meta-analysis added more weight. Researchers combined five randomized trials with 511 total participants and found vitamin D supplementation measurably reduced fibroid size compared to placebo. Genetic research backs this up from a different angle. A mendelian randomization study, which uses genetic data to test for cause and effect, found that higher vitamin D levels appeared to directly lower fibroid risk rather than just correlate with it.
Animal Research Shows What Vitamin D Might Be Doing
Before human trials caught up, lab work gave scientists a reason to keep looking. Researchers at the National Institute of Child Health and Human Development gave vitamin D to rats bred to grow uterine tumors. On average, treated rats ended up with tumors 75% smaller than untreated rats. That kind of result in an animal model doesn’t prove the same effect in women, but it gave scientists a strong reason to test the idea in people.
Why This Deserves More Than A Passing Mention From Doctors
Vitamin D deficiency is cheap and easy to test for and correct. Fibroids, by contrast, often mean surgery, blood loss, fertility struggles, and years of pain for millions of American women. If a basic vitamin test and an inexpensive supplement can meaningfully lower risk or slow growth, that is worth a five-minute conversation at a routine checkup, not a footnote buried in a review article.
Common sense says this: when 14 out of 14 studies point the same direction, and a federal research agency’s own study backs it up, patients deserve to hear about it plainly. Nobody is claiming vitamin D replaces surgery or cures fibroids outright. But ignoring a low-cost, low-risk factor that keeps showing up in study after study doesn’t serve women well, especially the Black women who are both more likely to be deficient and more likely to suffer from fibroids.
Women concerned about fibroids can ask their doctor for a simple 25-hydroxyvitamin D blood test. It’s inexpensive, widely available, and gives a clear number to work from. Given what the research keeps showing, that conversation seems overdue.
Sources:
mindbodygreen.com, pubmed.ncbi.nlm.nih.gov, pmc.ncbi.nlm.nih.gov, tandfonline.com, ijrcog.org
