Researchers discovered that women with lower vitamin D levels in their blood may be at higher risk for developing uterine fibroids—non-cancerous growths in the uterus. In a study of 171 women with fibroids and 125 women without them, scientists found that those with fibroids had significantly lower vitamin D levels. The study suggests a new vitamin D threshold of 14.34 ng/mL might be better for identifying women at risk of developing fibroids compared to current standards. This finding could help doctors identify and monitor women who might benefit from vitamin D supplementation to potentially prevent fibroid development.

The Quick Take

  • What they studied: Whether low vitamin D levels in the blood are connected to uterine fibroids and what vitamin D level best identifies women at risk
  • Who participated: 296 women aged 34-45 years old (171 with uterine fibroids and 125 without), matched by age, weight, and number of pregnancies
  • Key finding: Women with uterine fibroids had significantly lower vitamin D levels (12.79 vs. 16.19 ng/mL). A vitamin D level below 14.34 ng/mL showed the best ability to identify women at risk, with 70% accuracy in detecting who might develop fibroids.
  • What it means for you: If you’re a woman in your mid-30s to mid-40s, maintaining adequate vitamin D levels may help reduce your risk of developing uterine fibroids. However, this is one study and more research is needed before making major changes to your vitamin D intake.

The Research Details

This was a case-control study, which means researchers compared two groups: women who already had uterine fibroids (the cases) and women who didn’t have them (the controls). They measured vitamin D levels in everyone’s blood and looked for differences between the groups. The researchers carefully matched the two groups by age, body weight, and pregnancy history to make sure they were comparing similar people. This type of study is useful for finding connections between a health factor (vitamin D) and a health condition (fibroids), though it can’t prove that one directly causes the other.

Case-control studies are good at identifying potential risk factors for diseases. By comparing women with and without fibroids, researchers can spot patterns that might help doctors identify who’s at risk. This study is important because it suggests that current vitamin D guidelines—which were created based on bone health—might not be the best for predicting fibroid risk. Finding a better threshold could help doctors catch women at higher risk earlier.

The study had a reasonable sample size of 64 matched pairs, which provides decent statistical power. The researchers used careful matching to reduce bias. However, the study only included women aged 34-45, so results may not apply to younger or older women. The study was published in a peer-reviewed journal, which means other experts reviewed it. The cross-sectional nature means we can’t determine if low vitamin D causes fibroids or if fibroids somehow affect vitamin D levels.

What the Results Show

Women with uterine fibroids had significantly lower vitamin D levels compared to women without fibroids (12.79 ng/mL versus 16.19 ng/mL). This difference was statistically significant, meaning it’s unlikely to have happened by chance. When researchers used statistical models to account for other factors, they found that for every 1 ng/mL decrease in vitamin D, the risk of having fibroids increased by about 19-21%. The study identified a new vitamin D threshold of 14.34 ng/mL that performed better than existing standards for identifying women at risk. At this threshold, the test correctly identified 70.3% of women with fibroids and correctly identified 76.6% of women without fibroids, with an overall accuracy of 73.4%.

The researchers tested three existing vitamin D cutoff levels (12, 20, and 30 ng/mL) that are commonly used in medical practice, but found that the newly identified 14.34 ng/mL threshold performed better for fibroid risk specifically. This suggests that the current vitamin D guidelines, which were developed based on bone health research, may not be optimal for assessing fibroid risk.

Previous research has suggested a link between vitamin D and fibroids, but this study is among the first to propose a specific vitamin D threshold tailored to fibroid risk rather than using bone health standards. The findings align with other studies showing that vitamin D plays a role in reproductive health, though the exact mechanism isn’t fully understood. This research adds to growing evidence that vitamin D may be important for preventing fibroids.

The study only included women aged 34-45, so we don’t know if these findings apply to younger or older women. The study was relatively small (64 matched pairs), which limits how confident we can be in the results. Because this is a case-control study, we can’t determine whether low vitamin D causes fibroids or whether having fibroids somehow affects vitamin D levels. The study didn’t account for factors like sun exposure, diet, or supplements that affect vitamin D levels. The study was conducted in one location, so results may differ in other populations.

The Bottom Line

Women aged 34-45 should consider having their vitamin D levels checked, especially if they have risk factors for fibroids or a family history of them. Maintaining vitamin D levels above 14.34 ng/mL may help reduce fibroid risk, though more research is needed. This could involve getting moderate sun exposure, eating vitamin D-rich foods (like fatty fish, egg yolks, and fortified dairy), or taking supplements if recommended by your doctor. However, this is based on one study, so discuss vitamin D supplementation with your healthcare provider before starting.

Women aged 34-45 should pay attention to this research, particularly those with a family history of fibroids, irregular periods, or heavy menstrual bleeding. Women planning pregnancy may want to optimize their vitamin D levels. This research is less relevant for women outside this age range, though vitamin D is important for overall health at any age. Men don’t need to be concerned about this specific finding since it relates to uterine fibroids.

If you start optimizing your vitamin D levels, it may take several months to see changes in blood levels. The protective effect against fibroid development likely takes longer—possibly months to years—since fibroids develop gradually. You won’t notice immediate changes, but maintaining healthy vitamin D levels is a long-term health strategy.

Want to Apply This Research?

  • Track your vitamin D supplementation (if recommended by your doctor) and any symptoms like heavy periods, pelvic pain, or pressure. Log your vitamin D intake weekly and note any changes in menstrual symptoms monthly.
  • Set a reminder to take vitamin D supplements if prescribed, or to eat vitamin D-rich foods regularly. Track sun exposure time (aim for 10-30 minutes of midday sun several times per week, depending on skin type and location). Log dietary sources of vitamin D like fatty fish, fortified milk, or egg yolks.
  • Schedule annual vitamin D blood tests to monitor your levels and ensure they stay above the 14.34 ng/mL threshold identified in this study. Track any changes in menstrual patterns or pelvic symptoms. Review your vitamin D status with your doctor annually, especially if you’re in the 34-45 age range or have fibroid risk factors.

This research suggests a potential link between vitamin D levels and uterine fibroids, but it is not definitive proof of cause and effect. This information is for educational purposes only and should not replace professional medical advice. If you have concerns about uterine fibroids or vitamin D deficiency, consult with your healthcare provider before making any changes to your diet, supplements, or medical care. Individual vitamin D needs vary based on age, skin tone, geographic location, and other factors. Always discuss vitamin D supplementation with your doctor before starting, especially if you’re taking other medications or have existing health conditions.