Does Vitamin D Increase the Risk of Bleeding? A Look at the Evidence

October 18, 2025 •

4 min read

While vitamin D deficiency is widespread, affecting an estimated 1 billion people globally, the question of whether a normal or supplemented dose affects bleeding is complex. Research suggests the relationship between vitamin D and blood clotting is multifaceted, with effects ranging from influencing coagulation proteins to interacting with specific medications. This means the answer to does vitamin D increase the risk of bleeding? depends heavily on dosage and individual health factors.

Quick Summary

The link between vitamin D and bleeding risk is complicated. While deficiencies might increase risk in patients on blood thinners, extremely high levels could also be a factor, particularly with warfarin. More research is needed.

Key Points

Normal doses pose little risk: For most healthy people, taking standard, recommended doses of vitamin D supplements does not significantly increase the risk of bleeding.
Deficiency may increase bleeding in specific groups: Some studies show that vitamin D deficiency may be linked to an increased risk of gastrointestinal bleeding in patients who are also taking blood thinners.
High doses can affect warfarin users: Very high doses of vitamin D can potentially increase sensitivity to the anticoagulant warfarin, requiring careful dose monitoring to prevent bleeding.
Mechanism is complex: Vitamin D affects multiple parts of the coagulation system, demonstrating both anti-coagulant and anti-inflammatory properties, making its overall effect nuanced.
Talk to your doctor: If you take blood thinners or have a bleeding disorder, it is critical to consult a healthcare provider before taking vitamin D supplements, especially high-dose formulas.
Vitamin D and K interact: An imbalance between vitamin D and vitamin K can affect the function of vitamin K-dependent proteins, impacting overall cardiovascular and bone health.
Interaction with DOACs is minimal: There is no significant known interaction between vitamin D and direct oral anticoagulants (DOACs) like apixaban (Eliquis).

The relationship between vitamin D and blood coagulation is complex and has been a topic of growing scientific interest. While widely known for its role in bone health, research suggests that vitamin D also influences blood clotting processes. The idea that vitamin D could affect bleeding risk is not simple and depends on factors like dosage, individual health, and the use of medications, especially anticoagulants.

The Complex Role of Vitamin D in Coagulation

Vitamin D's influence on the blood clotting system involves a balance of both anti-coagulant and pro-coagulant properties. Studies indicate that vitamin D can regulate proteins vital to clotting. For example, it can decrease the expression of Tissue Factor (TF), a key clotting initiator, and increase thrombomodulin, an anti-coagulant. Vitamin D also possesses anti-inflammatory properties, which can indirectly help reduce abnormal clotting risk, particularly for those prone to cardiovascular issues. However, further large-scale studies are needed to fully understand the exact mechanisms.

The Connection Between Vitamin D Deficiency and Bleeding

Interestingly, a lack of vitamin D has been associated with a higher risk of bleeding in certain groups. A study found that vitamin D deficiency was linked to a greater risk of gastrointestinal (GI) bleeding in patients taking blood thinners. In this study, GI bleeding was almost twice as common in patients with low vitamin D levels. This was an observational study, so it shows an association rather than direct cause, highlighting the need for more research. Another study on patients with hereditary hemorrhagic telangiectasia (HHT), a condition causing abnormal blood vessels, observed that those with milder nosebleeds had higher vitamin D levels than those with severe nosebleeds, suggesting a protective effect of sufficient vitamin D.

High-Dose Vitamin D and Potential Risks

While deficiency has been linked to bleeding in some instances, very high doses of vitamin D may also be a concern, particularly in individuals taking warfarin. A study in 2019 noted a higher rate of major bleeding in warfarin users with serum vitamin D levels between 30-100 ng/mL compared to those with lower levels. This small study suggests a possible dose-related effect when vitamin D is combined with other blood thinners and indicates a need for more research.

Vitamin D and Anticoagulant Interactions

The most significant potential for bleeding risk with vitamin D occurs in patients using anticoagulant medications.

Warfarin (Coumadin) Interaction

Increased Sensitivity: Some research suggests that having adequate vitamin D levels might increase sensitivity to warfarin. One study found that patients with sufficient vitamin D had a higher warfarin sensitivity index than those who were deficient, potentially meaning they needed a lower dose of warfarin.
Managing Dosage: Due to this potential interaction, maintaining consistent vitamin D levels is important for individuals on warfarin. Starting or stopping a supplement can cause fluctuations that might affect the medication's effectiveness and increase the risk of bleeding or clotting.

Direct Oral Anticoagulants (DOACs)

Minimal Interaction: Generally, there is no known direct interaction between vitamin D and newer blood thinners like apixaban (Eliquis) or rivaroxaban (Xarelto). This is because DOACs function differently than warfarin and are not directly impacted by vitamin D status.

The Vitamin D and Vitamin K Connection

The relationship between vitamin D and vitamin K, both fat-soluble vitamins, adds another layer of complexity. Vitamin D encourages the creation of vitamin K-dependent proteins, which are essential for bone health and cardiovascular function and require vitamin K to work correctly. Some experts propose that boosting vitamin D without enough vitamin K could create an imbalance, possibly leading to inappropriate calcium buildup in arteries. While this is mainly related to cardiovascular health rather than direct bleeding risk, it highlights the complex interactions among fat-soluble vitamins.

Comparison: Vitamin D Levels and Bleeding Risk


Feature	Vitamin D Deficiency	High-Dose Vitamin D (Excess)
Impact on Bleeding	May increase bleeding risk, especially GI bleeding in patients on anticoagulants. Lower levels linked to more severe epistaxis in HHT patients.	May increase major bleeding risk in patients taking warfarin, as shown in some studies.
Interaction with Warfarin	Lower vitamin D status may be associated with a lower warfarin sensitivity index, potentially requiring higher doses.	Higher vitamin D levels may increase warfarin sensitivity, requiring careful dose management.
Cardiovascular Effects	Associated with increased risk of thrombotic events (blood clots).	Potential for hypercalcemia, which can damage blood vessels.
Overall Risk	Risk is higher in specific patient populations, particularly those on anticoagulants or with underlying conditions like HHT.	Risk is primarily a concern with very high, non-standard supplemental doses, especially when combined with medications like warfarin.

Conclusion: A Nuanced Answer

So, does vitamin D increase the risk of bleeding? For most healthy individuals taking recommended daily allowances, the answer is no; standard supplementation is not generally associated with blood thinning. However, the situation becomes more intricate with specific factors. Patients on blood thinners, particularly warfarin, should consult their healthcare provider before starting or changing vitamin D supplements, as vitamin D levels can affect medication effectiveness and dosage needs. Furthermore, evidence suggests that both low and extremely high levels of vitamin D might have implications for bleeding, especially when other risk factors or medications are involved. Due to the evolving nature of research, personalized medical advice based on your health profile is essential for managing potential risks safely.

For more information on the risks and benefits of vitamin D supplementation, speak with a healthcare professional. You can also consult resources from authoritative sources like the National Institutes of Health (NIH) Office of Dietary Supplements.

Frequently Asked Questions

It depends on the type of blood thinner. If you are taking warfarin (Coumadin), you must consult your doctor, as vitamin D levels can influence the medication's effectiveness and dosage requirements. For newer anticoagulants like apixaban (Eliquis), interactions are generally not a major concern, but informing your doctor about all supplements is always the safest approach.

Cod liver oil contains both vitamin D and omega-3 fatty acids, which have potential blood-thinning effects. The combination could affect your blood's clotting ability. If you take anticoagulant medication, discuss using cod liver oil with your healthcare provider.

In some studies, very high doses of vitamin D have been associated with a higher risk of major bleeding in patients taking warfarin. Extremely high, non-standard doses should be avoided unless specifically prescribed and monitored by a doctor, particularly in those with bleeding risk.

A vitamin D deficiency has been linked to an increased risk of bleeding in certain patient populations, especially those on blood thinners. For example, studies have shown a connection between low vitamin D levels and a higher incidence of gastrointestinal bleeding.

Vitamins D and K have a synergistic relationship, and vitamin D promotes the production of proteins that require vitamin K to function correctly in the coagulation process. An imbalance could potentially affect blood clotting, but more research is needed on the specific mechanism and its clinical significance.

Vitamin D toxicity, which is usually caused by excessive supplementation, leads to hypercalcemia (too much calcium in the blood). Symptoms can include fatigue, nausea, vomiting, increased thirst, confusion, and heart rhythm problems.

Yes, it is recommended to get your blood levels tested before adding a vitamin D supplement to your routine. This helps your healthcare provider determine the appropriate dosage for you and minimize any potential risks.