Vitamin K normally helps your blood clot so wounds don't bleed too much. Warfarin works against vitamin K, making your blood clot more slowly. How to get a steady amount of vitamin K It's up to you how much vitamin K you choose to eat.
And if you take a multivitamin that contains vitamin K, be sure you take it every day. Adding vitamin K If you want to start eating more of a food that's rich in vitamin K, talk to your doctor about how to add it safely.
Use this list to get an idea of what foods are sources of vitamin K. How vitamin K and warfarin affect your risks and your test results To find out how well warfarin is working, you will get blood tests to measure how long it takes for your blood to clot.
Vitamin K lowers your INR values. The lower your INR, the less time it takes for your blood to clot. A low INR means that warfarin isn't working well enough to prevent a dangerous blood clot. Warfarin raises your INR values.
The higher your INR, the more time it takes for your blood to clot. A high INR means that warfarin is working too well, so you bleed more quickly and easily. This can be dangerous. Keeping your warfarin and vitamin K intake steady every day helps keep you in a safe INR range.
References Citations Agricultural Research Service Credits Current as of: August 31, However, the importance of maintaining a healthy, balanced diet should be discussed because over-emphasising the effect of dietary vitamin K can lead to some patients restricting their diet to an excessive and unnecessary extent.
A change in INR may be observed when a patient moves between home and the hospital, resulting from changes in diet that can sometimes occur. Significant dose adjustments may be are required when moving between these settings. Soya protein may modestly reduce the effects of warfarin, therefore, patients wishing to use soya protein, especially if in complete substitution for animal protein, should be advised that it may lower INR and that a timely review may be necessary [13]. This could be owing to a combination of factors, including a change in diet and alcohol consumption.
INR can also be influenced by varying levels of physical activity. A subtherapeutic INR could be caused by a change in general medical condition. This can cause problems when a patient is acutely unwell, thus, close monitoring of INR may be necessary. Disease states that are known to decrease INR include hypothyroidism, diabetes mellitus, oedema, hyperlipidaemia and visceral carcinoma [14]. Disease states that are known to increase response to warfarin include congestive heart failure, hepatic dysfunction, moderate-to-severe renal impairment, hyperthyroidism, infectious disease, menstrual disorders, malnutrition and cachexia [14].
Improvements in disease status in these instances may cause a reduction in INR and necessitate an increase in warfarin dose. For example, careful monitoring of INR is recommended in patients with thyroid disease, as dose requirements may change depending upon changes in thyroid status — higher doses are required in hypothyroid states and lower doses in hyperthyroidism.
Likewise, careful monitoring of INR is required in congestive heart failure, as warfarin requirements can be increased or decreased depending on disease severity. Warfarin requirements have been found to change in the period following heart valve replacement surgery. In the immediate postoperative period, sensitivity to warfarin has been found to be increased.
However, this effect is not sustained and careful monitoring of response, with an increase in dose, may be necessary to avoid a subtherapeutic INR [18]. Warfarin dosage requirements can be affected by variations in the genes responsible for its metabolism or pharmacodynamic response. While genetic variations are not commonly tested for, they may be if a patient is particularly warfarin resistant.
Reduced clearance of warfarin is associated with variant alleles of CYP2C9, and patients expressing this phenotype require lower doses [14]. Warfarin exerts its anticoagulant effect by inhibiting vitamin K epoxide reductase, which controls the regeneration of reduced vitamin K from vitamin K epoxide. Reduced vitamin K is required for production of the vitamin K-dependent clotting factors.
Variations in the gene that encodes this, vitamin K epoxide reductase complex subunit 1 VKORC1 , has been associated with variations in warfarin dose requirements [14].
The action required depends on the risk of thrombosis and the cause of the low INR and this will vary depending on individual circumstances. As previously mentioned, BCSH guidelines advise that the use of bridging therapy should be considered if the INR becomes significantly subtherapeutic within the first month following an acute VTE.
The risk of thromboembolism is high in patients with prosthetic heart valves; however, this varies depending on the type of valve, position of valve and individual patient factors e. Bridging therapy may be required if an INR becomes subtherapeutic and it is necessary to follow local protocols, which may include referral to a cardiologist. The decision to cover with LMWH may be influenced by the type of valve, how subtherapeutic and how long the INR has been subtherapeutic for e.
LMWH may be instituted sooner for an older style mitral valve than a newer style aortic valve. The daily thrombosis risk of a non-anticoagulated heart valve is around 0. Any adjustments in warfarin dosage will be dependent on the reason s for the subtherapeutic INR.
A long-term cause e. However, it may not be appropriate to change the weekly warfarin dosage in the case of short-term causes e. A boost dose may occasionally be given if the patient is felt to be at higher thromboembolic risk. If the INR is low resulting from a long-term cause, then a boost dose may be given as well as increasing the total weekly dose.
Time must be given to allow the INR to change in response to a dose adjustment and although in hospitalised patients several INRs may be taken each week, it is important to take an overall weekly view of the warfarin dose and INR. The author has no relevant affiliations or financial involvement with any organisation or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.
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Oral anticoagulant therapy: important information for patients. Guidelines on oral anticoagulation with warfarin - fourth edition. British Journal of Haematology ;— Bridging anticoagulation: perioperative management of patients on anticoagulants. This is the time it takes for a blood clot to form. It is not necessary to cut out foods that contain vitamin K entirely. The foods that contain vitamin K also have other nutritional properties that contribute to a healthful diet.
It is important to note that the guidance varies on how much vitamin K people on warfarin can consume. For example, a recent systematic review suggests a diet that restricts vitamin K intake is unlikely to improve the efficacy of warfarin.
The authors suggest that keeping vitamin K levels consistent may be more beneficial. The average person only needs a small amount of vitamin K, around 60 to 80 micrograms mcg per day.
As this amount is so small, it can be easy for vitamin K levels to fluctuate across different days, creating a problem for people on warfarin. Keeping vitamin K levels stable, and within a normal range, may reduce its effect on the actions of warfarin. Keeping a food diary and being aware of foods that are high in vitamin K can help a person keep track.
Alcohol can also affect the action of warfarin and, therefore, the risk of developing blood clots. The AHA suggest that, on average, men should drink no more than one or two drinks per day, and women should drink no more than one drink per day. Drinking too much alcohol can be particularly harmful for people taking warfarin. A study of people in found that alcohol misuse has links to a higher risk of major bleeding in people taking warfarin. Warfarin can help to prevent dangerous blood clots.
It works by slowing the production of clotting factors, which the body makes by using vitamin K from food. People taking warfarin must avoid eating too many foods that are high in vitamin K, but it is not necessary to avoid these foods entirely. A stable diet, containing around 60 to 80 mcg of vitamin K is desirable.
People on warfarin must also ensure that they only consume alcohol in moderation.
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