Vitamins and Blood Thinners: Warfarin, Vitamin K, Vitamin E and Bleeding Risk

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Never start, stop or change a blood thinner or a vitamin on your own because of this page. If you take warfarin, your anticoagulation or warfarin clinic is the right place for questions about vitamins, supplements and diet. [1]

Signs of serious bleeding on warfarin include blood in urine or stool, unexplained bruising or nosebleeds, and coughing up or vomiting blood, and a sudden bad headache with confusion or weakness can mean bleeding in the brain. [1] Get urgent medical help; in the US call 911 for an emergency.

Why vitamin K matters with warfarin

Warfarin is a prescription anticoagulant used to prevent and treat blood clots, and its main side effect is a higher risk of bleeding. [1] Vitamin K is the vitamin the body uses for blood clotting. [2]

What the sources say:

• The NHS says not to take vitamin K supplements while on warfarin. [1]


• Foods high in vitamin K, such as broccoli, spinach and other leafy greens, can affect how warfarin works. The NHS says you can still eat them but should talk to your warfarin clinic. [1]


• MedlinePlus says sudden changes in vitamin K consumption can change the effect of the medicine, and that it is important to keep vitamin K levels constant day to day. [3]


• The NHS adds that you should talk to your doctor before making big changes to your diet. [1]

So the documented message is consistency and clinic guidance, not "avoid green vegetables." Warfarin treatment includes regular INR blood tests of how quickly your blood clots, and your dose may change based on the results. [1] See Vitamin K for food sources and the K1 and K2 forms.

A trial of daily vitamin K, and its limits

One randomized trial gave 200 patients of a Leiden anticoagulation clinic, who used the blood thinner phenprocoumon, either 100 mcg of vitamin K a day or placebo for 24 weeks. Time in the target INR range was 85.5% on placebo and 89.5% with vitamin K; the 3.6-point difference was not statistically clear (95% CI -0.8 to 8.0). [4] This was a clinic-supervised study amount in a different drug, not advice, and it does not show that supplements are safe for people on warfarin.

Vitamin E and bleeding

• MedlinePlus says high doses of vitamin E supplements (alpha-tocopherol) might increase the risk of bleeding in the brain (hemorrhagic stroke). [5]
• Cases of a stronger anticoagulant effect have been reported with high-dose vitamin E. A pair of 12-week trials of 1,000 IU a day in people not on anticoagulants found a rise in PIVKA-II, a marker of poorer vitamin K status, and the authors said high doses of vitamin E may antagonize vitamin K. They also said the clinical significance needs further investigation. [6]
• Limits: those trials measured a lab marker, not bleeding events, in people not on blood thinners.

Official upper limits for vitamin E differ: EFSA lists 300 mg a day for adults and says a review is ongoing, and the NHS says 540 mg (800 IU) or less a day of supplements is unlikely to cause harm. [7][8] These are general-population limits, not guidance for someone on a blood thinner.

Other things that change bleeding risk

The NHS warfarin page also lists anti-inflammatory painkillers such as ibuprofen or aspirin, antibiotics, statins and St John's wort as things that may not mix well with warfarin. [1] For fish oil, see Omega-3 safety and interactions. Vitamins A, B and C and the newer anticoagulants: Proper evidence not found in the pages read for this page (NHS warfarin, MedlinePlus, PubMed), so do not assume either way; ask your clinic.

Surgery, pregnancy, kidney and liver conditions

Tell your doctor or dentist you take warfarin before any procedure; carry the anticoagulant alert card. [1] Warfarin may not suit people who have liver or kidney problems or are about to have surgery, and it is not usually used in pregnancy. [1] Supplements before surgery are covered at Vitamins before surgery and Supplements before surgery. Check other medicines in the interactions reference table, and ask a pharmacist about product quality and the real vitamin K or E content on the label (Quality testing and certifications).