Vitamin K is fundamental to bone health, blood clotting and cardiovascular protection. Less prominent than some vitamins, it nevertheless has a major impact, particularly for active people and athletes.

What is vitamin K, and why does it matter?

Vitamin K is a fat-soluble vitamin essential for blood clotting, bone health and cardiovascular protection.

It activates proteins with vital functions, including preventing bleeding, strengthening bones and limiting arterial calcification.

There are two main forms:

Vitamin K1, or phylloquinone, found in leafy green vegetables.
Vitamin K2, or menaquinone, found in fermented foods and animal products.

Main functions of vitamin K

Vitamin K has important roles across different tissues. The main ones include:

Blood clotting: essential for producing clotting proteins, including prothrombin.

Deficiency can cause frequent bruising, nosebleeds, bleeding gums and even internal bleeding.

Bone health: K2 activates osteocalcin, enabling calcium to bind correctly to bone. Without activation, calcium may fail to reach bone and accumulate in tissues such as arteries instead.
Cardiovascular protection: vitamin K also activates MGP, a protein preventing calcium deposition in arteries. This helps maintain arterial elasticity and prevent atherosclerosis.

Vitamin K therefore regulates calcium, helping it reach bones and preventing accumulation elsewhere.

Vitamin K1 vs K2

K1 comes mainly from leafy greens and is associated with clotting. K2 occurs in animal and fermented foods and helps direct calcium to bones while preventing arterial deposition.

Daily recommendations by age and life stage

Adult men are generally advised to consume 120 mcg/day and women 90 mcg/day.

These remain unchanged during pregnancy or breastfeeding unless a doctor advises otherwise.

Foods rich in vitamin K1 (phylloquinone)

K1 is the most common dietary form. Plant sources include spinach, kale, chard, dark lettuce, broccoli, Brussels sprouts, parsley, basil, coriander, soya and olive oils, kiwi, grapes, peas and avocado.

Darker green vegetables generally contain more vitamin K.

Foods rich in vitamin K2 (menaquinone)

Sources include natto, or fermented soya, kefir, sauerkraut, miso, egg yolks, liver, aged cheeses such as Gouda and Edam, and salmon.

What affects vitamin K absorption?

The role of dietary fats

Vitamin K is absorbed better alongside healthy fats. Pair it with avocado, olive oil, nuts, seeds or oily fish to maximise its use.

Antibiotics and digestive conditions

Prolonged antibiotic use may disrupt gut flora and natural K2 production.

Conditions impairing fat absorption, including Crohn’s disease, coeliac disease or bariatric surgery, may also reduce vitamin K absorption.

Who needs to monitor vitamin K intake?

People taking anticoagulants or warfarin

Vitamin K can interfere with some anticoagulants. Do not eliminate it: maintain consistent intake and regular medical monitoring so medication doses can be adjusted.

Why medical supervision matters

Medical monitoring is essential: check INR and adjust medication according to diet.

Keep vitamin K intake consistent and controlled with professional guidance rather than eliminating it.

Everyday ways to include vitamin K foods

Add a daily portion of green vegetables to salads, stir-fries or soups.
Use extra virgin olive oil as your main cooking fat.
Include fermented foods such as kefir, sauerkraut or miso.
Choose aged cheeses or eggs.

Conclusion:

Vitamin K supports overall health. Adequate intake through a varied diet can make a meaningful difference to wellbeing.

Vitamin K-Rich Foods: Benefits, Types and Natural Sources