Vitamin K: not just clotting – bones and heart

What is vitamin K?

Vitamin K is a fat-soluble vitamin that exists in two main forms. K1 (phylloquinone) is found primarily in green leafy vegetables such as spinach, kale, and broccoli. K2 (menaquinone) is found in fermented foods such as natto, hard cheeses, and fermented dairy products. Although both forms support coagulation, their roles in the body differ significantly.

How does vitamin K affect bones?

K2 activates osteocalcin, a protein produced by bone-forming cells (osteoblasts). Activated osteocalcin binds calcium to the bone matrix, making bones stronger and denser. Studies show that adequate K2 intake is associated with reduced risk of osteoporosis and fractures, particularly in postmenopausal women and older adults.

Vitamin K and blood vessels

Matrix Gla Protein (MGP) is one of the most potent inhibitors of arterial calcification known. Without sufficient K2, MGP remains inactive and cannot prevent calcium from depositing in artery walls. Over time, this leads to arterial stiffening and increased cardiovascular risk. K2 activates MGP, keeping arteries flexible and clear.

K1 and K2 – are they the same?

No. K1 is used primarily by the liver for coagulation factor synthesis and is rapidly metabolised. K2, especially the MK-7 subtype, has a longer half-life and reaches peripheral tissues including bones and arteries. Natto (fermented soybeans) is by far the richest dietary source of K2 (MK-7). Other sources include gouda, brie, egg yolk, butter, and chicken liver.

Who may face deficiency?

Several groups are at higher risk of vitamin K deficiency:

• People on long-term antibiotic therapy (antibiotics reduce gut bacteria that produce K2)
• Those with intestinal diseases (Crohn's, coeliac, short bowel syndrome) that impair fat absorption
• People with very low vegetable intake
• Older adults with reduced dietary variety
• Newborns (routinely given K1 at birth)

Practical checklist

1. Include green leafy vegetables (spinach, kale, broccoli) in your diet daily. 2. Add fermented foods – natto, hard cheeses, fermented dairy – several times per week. 3. Pair vitamin K-rich foods with healthy fats to improve absorption (it is fat-soluble). 4. If you take anticoagulants (warfarin), do NOT change your vitamin K intake without consulting your doctor – it directly affects INR. 5. Consider a combined vitamin D3 + K2 supplement if your diet is low in both, after discussing with a healthcare professional.

When to see a doctor immediately?

Seek prompt medical attention if you notice:

• Unusual or excessive bruising without clear cause
• Bleeding gums or prolonged bleeding after minor cuts
• Wounds that are slow to heal
• If you are on anticoagulant therapy (warfarin/acenocoumarol), ensure regular INR monitoring and never adjust your dose or diet dramatically without medical guidance.