Can Vitamin D Cause Bleeding? Separating Fact from Risk

October 6, 2025 •

3 min read

According to a 2019 study, warfarin-treated patients with higher serum vitamin D levels had an increased risk of major bleeding, a finding that adds nuance to the question: can vitamin D cause bleeding? While moderate vitamin D intake is generally safe, the relationship with bleeding is far from simple and depends on both deficiency and excess levels.

Quick Summary

The connection between vitamin D and bleeding is complex, influenced by dosage and pre-existing health conditions. High doses and toxicity can potentially increase risk via hypercalcemia, while deficiency has also been linked to specific bleeding events.

Key Points

High Doses & Toxicity: Excessive vitamin D intake can lead to hypercalcemia (high blood calcium), which damages blood vessels and may increase bleeding risk.
Drug Interactions: High or sufficient vitamin D levels may affect the required dose of warfarin, potentially increasing bleeding risk if not properly monitored.
Deficiency & Bleeding: Paradoxically, vitamin D deficiency has been linked to an increased risk of gastrointestinal bleeding in patients on blood thinners and more severe epistaxis in certain conditions.
Underlying Conditions: Pre-existing health issues like liver and kidney disease, often associated with vitamin D deficiency, can independently increase a person's bleeding risk.
Platelet Function: Vitamin D may influence platelet count and aggregation, with some studies showing an inhibitory or anti-thrombotic effect.
Proper Management is Key: The safest approach is to take recommended doses and consult a healthcare provider, especially if you have risk factors for bleeding or are on anticoagulant medication.

The Dual Nature of Vitamin D: Coagulation and Anti-Coagulation

Vitamin D is a fat-soluble vitamin known for bone health but also influences blood clotting. This complex relationship isn't a simple cause of blood thinning or clotting; vitamin D modulates proteins and factors in both clot formation and dissolution. Some research suggests it can act as an anticoagulant by regulating proteins like thrombomodulin and tissue factor. It may also reduce platelet counts and aggregation. These effects highlight that vitamin D's influence on the hemostatic system is about balance.

When High Doses of Vitamin D Increase Bleeding Risk

Excessively high vitamin D intake (toxicity or hypervitaminosis D) is a health risk, primarily causing hypercalcemia (high blood calcium). Severe hypercalcemia can damage organs and blood vessels, potentially increasing bleeding risk.

NHS England highlighted a case where high-strength vitamin D was linked to a death from intestinal bleeding caused by hypercalcemia. A 2019 study also found warfarin-treated patients with higher vitamin D levels had a significantly higher rate of major bleeding events.

The Unexpected Paradox: Low Vitamin D and Bleeding

Surprisingly, low vitamin D levels can also be associated with increased bleeding risk. A study linked deficiency to a higher risk of gastrointestinal (GI) bleeding in patients taking blood thinners, with nearly double the rates in the deficient group. This might relate to vitamin D's role in inflammation and endothelial function. In patients with Hereditary Hemorrhagic Telangiectasia (HHT), higher vitamin D levels were associated with less severe nosebleeds.

The Critical Interaction with Warfarin

The interaction between vitamin D and warfarin is crucial. Warfarin inhibits vitamin K, affecting clotting factors. Vitamin D can influence various coagulation factors, complicating warfarin therapy. A study suggested vitamin D status might affect warfarin sensitivity, with sufficient levels trending towards higher sensitivity. This necessitates careful monitoring and dose adjustments when changing vitamin D supplementation.

Comparison Table: Vitamin D Deficiency vs. High-Dose Toxicity


Feature	Vitamin D Deficiency	High-Dose Vitamin D Toxicity
Mechanism influencing bleeding	Indirectly, potentially through altered coagulation and inflammatory pathways.	Directly, through hypercalcemia causing vascular damage and tissue damage.
Associated bleeding type	Increased risk of gastrointestinal bleeding in patients on blood thinners. More severe epistaxis (nosebleeds) in specific conditions like HHT.	Gastrointestinal bleeding, potentially fatal, linked to severe hypercalcemia. Higher rates of major bleeding in some warfarin patients with elevated levels.
Primary risk factor	Inadequate sun exposure, dietary intake, or underlying conditions affecting absorption.	Excessive supplementation, particularly in unsupervised or very high-dose regimens.
Patient population at risk	Individuals with chronic liver or kidney disease, limited sun exposure, and those on blood thinners.	Individuals taking very high supplemental doses, potentially those with pre-existing conditions affecting calcium metabolism.
Management	Appropriate supplementation under medical supervision to reach sufficient levels.	Discontinuation of supplementation and management of hypercalcemia.

Underlying Conditions That Influence Bleeding Risk

Conditions like chronic liver disease, often involving vitamin D deficiency and impaired clotting factor production, increase bleeding risk. Chronic kidney disease (CKD) patients also frequently have low vitamin D levels and higher bleeding risk, requiring careful management.

Conclusion: Finding the Right Balance

The potential for vitamin D to influence bleeding exists at both deficiency and excess levels, though it's not a simple cause-and-effect. While generally safe at recommended doses, individuals on blood thinners or with conditions like liver or kidney disease face a more complex situation. High doses risk hypercalcemia and vascular damage, while deficiency might increase bleeding in certain contexts. Always consult a healthcare provider before changing vitamin D intake, especially with bleeding risk factors or anticoagulant use. Monitoring is crucial for a safe balance. For more information on hypervitaminosis D risks, see MedlinePlus Hypervitaminosis D Information.

Frequently Asked Questions

If you are on a blood-thinning medication like warfarin, you must inform your doctor before taking vitamin D supplements. While low doses are generally considered safe, higher doses or changing your vitamin D status can alter your sensitivity to warfarin and potentially increase bleeding risk.

Yes, research indicates a link between vitamin D deficiency and increased bleeding risk in certain situations. For example, a study found that vitamin D deficiency was associated with a higher risk of gastrointestinal bleeding in patients on blood thinners.

Vitamin D toxicity, or hypervitaminosis D, can cause symptoms related to high blood calcium (hypercalcemia). These include fatigue, nausea, vomiting, confusion, irritability, and frequent urination. Severe cases can lead to serious complications like kidney damage and even bleeding issues.

Vitamin D is thought to influence blood clotting by regulating proteins involved in both clot formation (e.g., tissue factor) and breakdown (e.g., thrombomodulin). It also affects the function and number of platelets, which are crucial for clotting.

Hypercalcemia is a condition where the level of calcium in your blood is abnormally high. This can occur from excessive vitamin D intake and, if severe, can lead to widespread tissue damage, including damage to blood vessels.

In rare but severe cases, excessively high doses of vitamin D can lead to hypercalcemia, which has been linked to intestinal bleeding. A coroner's concern in the UK was related to an instance of fatal intestinal bleeding caused by hypercalcemia due to vitamin D overdose.

While the interaction with warfarin is most studied, very high doses of vitamin D can potentially interact negatively with other blood thinners as well. Regardless of the medication, it's essential to discuss all supplements, including vitamin D, with your healthcare provider.