Vitamin K for bruising is a topic of interest for individuals experiencing easy bruising, as this fat-soluble vitamin plays an essential role in blood clotting. Vitamin K acts as a cofactor for enzymes that activate clotting factors in the liver, and deficiency can impair the body's ability to form stable clots, leading to increased bruising. Whilst true vitamin K deficiency is uncommon in healthy UK adults, it may occur in those with malabsorption disorders, severe liver disease, or following prolonged antibiotic use. However, easy bruising has numerous causes beyond vitamin K deficiency, including medications, blood disorders, and age-related changes, making proper medical assessment essential before considering supplementation.

What Is Vitamin K and How Does It Help With Bruising?

Vitamin K is a fat-soluble vitamin essential for blood clotting and bone health. The name derives from the German word 'Koagulation', reflecting its critical role in the coagulation cascade. There are two main naturally occurring forms: vitamin K1 (phylloquinone), found predominantly in green leafy vegetables, and vitamin K2 (menaquinone), produced by bacteria in the gut and present in fermented foods and animal products.

The connection between vitamin K and bruising relates directly to its function in blood clotting. Vitamin K acts as a cofactor for the enzyme gamma-glutamyl carboxylase, which activates several clotting factors in the liver, including factors II (prothrombin), VII, IX, and X, as well as the anticoagulant proteins C and S. Without adequate vitamin K, these proteins cannot function properly, leading to impaired coagulation. When blood vessels are damaged—even from minor trauma—the body struggles to form stable clots, resulting in blood leaking into surrounding tissues and manifesting as bruises (ecchymoses).

When vitamin K deficiency occurs, individuals may notice they bruise more easily than usual, experience prolonged bleeding from minor cuts, or develop spontaneous bruising without apparent injury. However, it is important to note that easy bruising has numerous potential causes beyond vitamin K deficiency, including certain medications (particularly anticoagulants and antiplatelet agents), blood disorders, liver disease, and age-related changes to skin and blood vessels.

In the UK, true vitamin K deficiency is relatively uncommon in healthy adults due to adequate dietary intake and some contribution from bacterial synthesis in the intestines, though this source is variable and not reliably sufficient. The condition is more frequently observed in newborns (hence routine vitamin K prophylaxis at birth as recommended by NICE), individuals with malabsorption disorders (such as coeliac disease or inflammatory bowel disease), those with severe liver disease, or patients taking certain medications that interfere with vitamin K metabolism, including warfarin, some cephalosporins, and broad-spectrum antibiotics that reduce gut flora.

Causes of Easy Bruising and Vitamin K Deficiency

Easy bruising can result from multiple mechanisms, and whilst vitamin K deficiency is one potential cause, it represents only a small proportion of cases. Understanding the broader differential diagnosis is essential for appropriate management.

Primary causes of vitamin K deficiency include inadequate dietary intake (rare in developed countries), malabsorption syndromes affecting fat absorption (since vitamin K is fat-soluble), prolonged antibiotic use that disrupts gut bacteria producing vitamin K2, severe liver disease impairing synthesis of clotting factors, and certain medications. Conditions such as coeliac disease, Crohn's disease, ulcerative colitis, chronic pancreatitis, and biliary obstruction can all compromise vitamin K absorption. Additionally, individuals who have undergone bariatric surgery or have short bowel syndrome may be at increased risk.

Other common causes of easy bruising unrelated to vitamin K include advancing age (as skin becomes thinner and blood vessels more fragile), medications such as corticosteroids (which weaken blood vessel walls and thin skin), NSAIDs, SSRIs, anticoagulants and antiplatelet medications (aspirin, clopidogrel, warfarin, DOACs), blood disorders such as thrombocytopenia or clotting factor deficiencies, vasculitis, vitamin C deficiency (scurvy), and inherited conditions like von Willebrand disease or haemophilia.

When to seek medical assessment: NICE guidance (NG12) recommends an urgent full blood count within 48 hours for adults with unexplained bruising or bleeding to assess for possible leukaemia. Patients should contact their GP if they experience sudden onset of easy bruising without explanation, bruising accompanied by other bleeding symptoms (nosebleeds, bleeding gums, blood in urine or stools), petechiae (pinpoint red spots), large or painful bruises, or bruising in unusual locations (trunk, face). Seek immediate medical attention (999/A&E) for severe bleeding or symptoms of haemodynamic compromise (dizziness, shortness of breath, rapid heart rate).

Blood tests including full blood count, clotting screen (PT/INR, APTT), and liver function tests can help identify the underlying cause. Vitamin K deficiency specifically prolongs the prothrombin time (PT/INR) whilst initially preserving the APTT, though both may eventually become prolonged in severe cases.

How to Use Vitamin K for Bruising: Dosage and Forms

Vitamin K supplementation should only be undertaken following proper medical assessment and diagnosis of deficiency. Self-prescribing vitamin K without medical guidance is not recommended, particularly for individuals taking anticoagulant medications, as it can interfere with their therapeutic effect.

Oral vitamin K supplements are available in the UK as food supplements, typically containing vitamin K1 (phylloquinone) in doses ranging from 10-200 micrograms per tablet. These are not licensed medicines and are not indicated to treat vitamin K deficiency. For medically diagnosed deficiency, licensed phytomenadione (vitamin K1) preparations should be used according to BNF/SmPC guidance, with dosing and monitoring determined by a healthcare professional based on the severity of deficiency and underlying cause. Response to treatment can be monitored through repeat coagulation studies, with improvement in PT/INR typically observed within 24–48 hours of adequate vitamin K administration.

For individuals with malabsorption disorders, oral vitamin K may be poorly absorbed, necessitating alternative routes of administration. In such cases, parenteral vitamin K (phytomenadione) may be required, administered in hospital or specialist settings. Intravenous administration should be given slowly with monitoring due to the risk of hypersensitivity reactions, as advised in the SmPC. Intramuscular injections should be avoided in patients with coagulopathy or those taking anticoagulants due to haematoma risk.

Topical vitamin K preparations are marketed for bruising, particularly post-procedural bruising following cosmetic treatments. However, there is limited robust clinical evidence supporting their efficacy, and they are not routinely recommended for bruising reduction in clinical practice.

Important safety considerations: Patients taking warfarin should never take vitamin K supplements without medical supervision, as even small amounts can significantly reduce anticoagulant efficacy and increase thrombotic risk. Those on direct oral anticoagulants (DOACs) should similarly consult their healthcare provider before supplementation, though vitamin K does not reverse DOAC anticoagulation. Standard phytomenadione (K1) supplements have an excellent safety profile. The historical concern about haemolysis risk in glucose-6-phosphate dehydrogenase (G6PD) deficiency applies specifically to older menadione/menadiol derivatives, which are not used in modern supplements or medicines in the UK.

If you experience any suspected side effects from vitamin K supplements or medicines, report them to the MHRA Yellow Card scheme.

Vitamin K-Rich Foods and Dietary Sources

For most individuals, obtaining adequate vitamin K through diet is straightforward and represents the safest, most physiological approach to maintaining optimal vitamin K status. The UK does not have a formal Reference Nutrient Intake (RNI) for vitamin K, but adequate intake is estimated at approximately 1 microgram per kilogram of body weight daily for adults (roughly 70–80 micrograms for an average adult), according to NHS guidance.

Excellent sources of vitamin K1 include dark green leafy vegetables, which contain particularly high concentrations. Kale leads the list with approximately 390 micrograms per 100g (cooked), followed by spinach (380 micrograms per 100g cooked), spring greens (340 micrograms per 100g), Brussels sprouts (140 micrograms per 100g), and broccoli (110 micrograms per 100g). Other good sources include cabbage, lettuce (particularly darker varieties), asparagus, green beans, peas, and herbs such as parsley and basil.

Vitamin K2 sources include fermented foods and animal products. Natto (fermented soybeans, popular in Japanese cuisine) contains exceptionally high levels but is less commonly consumed in the UK. More accessible sources include hard cheeses (particularly Gouda and Edam), soft cheeses, egg yolks, butter, chicken, and beef liver. Certain vegetable oils, particularly soybean oil, rapeseed oil, and olive oil, also contribute meaningful amounts of vitamin K1.

Practical dietary advice: Incorporating one to two servings of green leafy vegetables daily typically provides adequate vitamin K for most individuals. Since vitamin K is fat-soluble, consuming these vegetables with a small amount of fat (such as olive oil in a salad dressing or butter on cooked greens) enhances absorption. Cooking methods have minimal impact on vitamin K content, as it is relatively heat-stable, though some loss occurs with prolonged boiling.

Special considerations: Patients taking warfarin require consistent vitamin K intake rather than avoidance, as fluctuating dietary vitamin K causes unstable INR control. The NHS advises these patients to maintain steady consumption of vitamin K-rich foods rather than eliminating them entirely. Individuals following restrictive diets (such as very low-fat diets) or those with limited vegetable intake may benefit from dietary counselling to ensure adequate vitamin K consumption. For those unable to meet requirements through diet alone due to malabsorption or other medical conditions, supplementation under medical supervision may be appropriate.

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