Does Vitamin D3 and K2 Shrink Fibroids? Unpacking the Research

October 13, 2025 •

4 min read

According to a 2024 meta-analysis, women with uterine fibroids exhibit significantly lower serum vitamin D levels compared to those without the condition. This key finding has spurred interest in whether supplementing with vitamins, particularly vitamin D3 and K2, can help manage or even shrink fibroids. While vitamin D3 shows promising potential as an anti-fibrotic agent, the evidence for vitamin K2's impact on fibroids is currently limited.

Quick Summary

Reviewing current scientific literature on the relationship between vitamin D3, K2, and uterine fibroids. Summarizes findings on vitamin D's anti-growth effects and addresses the lack of direct evidence for vitamin K2's efficacy. Distinguishes between prevention and potential fibroid shrinkage based on clinical and observational studies.

Key Points

Vitamin D3 inhibits fibroid growth: Research shows vitamin D3 acts as an anti-proliferative and anti-fibrotic agent, suppressing fibroid cell growth and excess extracellular matrix production.
Vitamin D3 may modestly shrink fibroids: While not a cure, some smaller human trials on vitamin D-deficient women show that supplementation may lead to a modest reduction in fibroid size.
Vitamin K2's direct fibroid effect is negligible: Current literature suggests vitamin K2 has little to no direct influence on the size or growth of uterine fibroids.
Vitamin K2 supports calcium metabolism: When taken with vitamin D3, vitamin K2 helps regulate calcium, directing it to bones and potentially preventing soft tissue calcification.
Vitamin D deficiency is linked to fibroids: Many studies show an inverse correlation between serum vitamin D levels and the presence or volume of uterine fibroids.
Supplements are not a standalone cure: Vitamin supplementation should be part of a broader, medically supervised treatment plan, not a replacement for conventional medical care for fibroids.
Diet and lifestyle are also crucial: A diet rich in fruits, vegetables, and omega-3s, and low in red meat and processed foods, can support overall uterine health and potentially mitigate fibroid growth.

Understanding the Link Between Vitamin D3 and Fibroids

Research has increasingly focused on the association between vitamin D deficiency and the development of uterine fibroids. A significant body of evidence from preclinical, observational, and clinical studies suggests that sufficient vitamin D levels may play a protective and therapeutic role. The mechanism behind this is linked to vitamin D's properties as a prohormone, influencing cellular processes critical for fibroid growth.

The Anti-Proliferative and Anti-Fibrotic Mechanisms of Vitamin D3

The anti-fibroid effects of vitamin D3 are rooted in its ability to modulate key cellular and genetic pathways involved in fibroid formation and growth. The active form of vitamin D3, 1,25-dihydroxyvitamin D3, interacts with vitamin D receptors (VDRs) found in uterine fibroid cells. This interaction initiates a cascade of effects, including:

Growth Inhibition: Vitamin D3 reduces the expression of proteins that promote cell proliferation, such as PCNA and MKI67, and increases pro-apoptotic (cell-death-inducing) proteins. This effectively puts the brakes on the abnormal cell growth characteristic of fibroids.
Antifibrotic Action: A core feature of fibroids is the overproduction of extracellular matrix (ECM) proteins, like collagen, which leads to tissue fibrosis. Vitamin D3 acts as a potent antifibrotic agent by suppressing the expression of profibrotic factors, especially the growth factor TGF-β3, which drives ECM overproduction.
Inhibition of Inflammation: Chronic inflammation can contribute to fibroid development. Vitamin D has anti-inflammatory properties that can help mitigate this aspect of the disease.

Can Vitamin D3 Cause Fibroid Shrinkage?

While the evidence for inhibiting growth is strong, the question of whether vitamin D3 can shrink existing fibroids has yielded mixed results in human trials. Some smaller studies have shown a significant decrease in fibroid size in women with vitamin D deficiency who received supplementation. For example, a 2019 study in Iran observed a 7.14mm reduction in fibroid size in a group of women treated with vitamin D3, while the placebo group saw an increase. However, other studies have found that while supplementation may halt fibroid growth, it does not lead to a statistically significant reduction in size over a short period. This suggests that vitamin D's primary role may be to prevent growth and recurrence rather than reverse established large fibroids, though more research is needed.

The Role of Vitamin K2 in Relation to Fibroids

When considering supplementation with vitamin D3, some experts suggest pairing it with vitamin K2, mainly to support proper calcium metabolism. However, the direct impact of vitamin K2 on uterine fibroids is currently considered negligible based on available data.

Vitamin K2's primary mechanism is the activation of Matrix Gla Protein (MGP), which helps direct calcium to the bones and prevents its accumulation in soft tissues and arteries. While fibroid tissue can sometimes calcify, there is no direct evidence linking vitamin K2 to the prevention or treatment of fibroid calcification. Any potential anti-inflammatory or anti-tumor effects are, at present, speculative and not specific to uterine fibroids.

Comparing the Roles of Vitamin D3 and K2 for Fibroids


Feature	Vitamin D3 and Fibroids	Vitamin K2 and Fibroids
Research Evidence	Substantial preclinical and promising clinical evidence supporting growth inhibition and a potential link to shrinking.	Extremely sparse and indirect literature; currently considered to have a negligible direct influence.
Key Mechanism	Acts as an antifibrotic and anti-proliferative agent, inhibiting cell growth and ECM production.	Regulates calcium metabolism and activates proteins that prevent soft tissue calcification, including arteries.
Effect on Fibroids	Shows potential to halt growth and may modestly reduce size, especially in deficient individuals.	No direct evidence of shrinking fibroids. Role in fibroid health is indirect and largely hypothetical.
Therapeutic Recommendation	Often recommended for women with fibroids, especially if deficient, but as a supportive measure, not a standalone cure.	Not typically recommended as a primary treatment for fibroids due to lack of specific evidence.
Primary Function in Supplement	Primary active component targeting cellular pathways of fibroid development.	Included to ensure proper calcium distribution, reducing theoretical risks associated with high-dose D3 supplementation.

Important Considerations for Supplementation

While some studies offer encouraging results, the consensus among healthcare professionals is that vitamin D supplementation should be considered a supportive measure rather than a cure for fibroids. It is particularly relevant for women with a diagnosed vitamin D deficiency, which is prevalent in women with fibroids.

It is crucial to work with a doctor or registered dietitian to determine the appropriate dosage and duration of supplementation. High doses of any vitamin without medical supervision can be unsafe. A holistic approach to managing fibroids, which includes dietary changes and exercise, is typically recommended alongside medical treatment.

A Broader Nutritional Perspective on Fibroids

Beyond specific supplements, overall dietary habits can influence fibroid growth. Estrogen-driven growth means that certain foods can either promote or inhibit fibroid development.

Foods to Embrace: Diets rich in fruits, vegetables, whole grains, and fatty fish high in omega-3s are recommended. A high-fiber diet helps regulate estrogen levels, and antioxidants combat inflammation.
Foods to Limit: Consumption of red meat, processed foods, and high-fat dairy has been linked to an increased risk or exacerbation of fibroids. Limiting alcohol and caffeine may also be beneficial.

Conclusion

The question, does vitamin D3 and K2 shrink fibroids?, has a nuanced answer. While vitamin D3 demonstrates significant potential to inhibit fibroid cell growth and has been shown in some small studies to reduce fibroid size, it is not a guaranteed cure. The evidence for vitamin K2's specific role in shrinking fibroids is currently lacking, though it plays an important supporting role in calcium regulation when supplementing with vitamin D3. A sufficient vitamin D level is consistently associated with a reduced risk and slower growth of fibroids. However, supplementation should always be managed under medical guidance as part of a broader treatment plan that may include lifestyle changes and other medical interventions. Patients should prioritize discussing all treatment options with a healthcare provider.

Explore more comprehensive details on the mechanisms of vitamin D in fibroid biology here.

Frequently Asked Questions

No. While vitamin D3 has shown potential to inhibit fibroid growth and may lead to modest shrinkage in some cases, neither vitamin D3 nor K2 can eliminate fibroids completely. They are considered supportive therapies, not cures.

Vitamin D3 helps inhibit fibroid growth by acting as an anti-proliferative agent, slowing down the multiplication of fibroid cells. It also has an anti-fibrotic effect, reducing the excess collagen and extracellular matrix that cause fibroids to grow.

Vitamin K2 is primarily paired with vitamin D3 to ensure calcium is properly utilized. Vitamin D3 helps with calcium absorption, while K2 directs that calcium to the bones and prevents it from accumulating in soft tissues, like arteries.

You should not start any supplementation without consulting a healthcare professional. A doctor can determine if you have a vitamin D deficiency and recommend the appropriate dosage. Self-treatment with supplements is not advised.

Yes. Lifestyle changes such as maintaining a healthy weight, eating a diet rich in fruits, vegetables, and fiber, and limiting red meat and processed foods are all recommended. Some studies also explore compounds found in green tea.

Clinical trials have assessed the effects over periods ranging from 10 weeks to several months. While some studies observed changes in fibroid size within this timeframe, the long-term effects and the time required for significant change are still being investigated.

Research suggests that while vitamin D may help inhibit the growth of fibroids, it might not cause significant shrinkage, especially for larger, established tumors. It is potentially more effective as a preventive measure or for slowing the growth of smaller fibroids.