Heart: "Vitamin K activates proteins that protect blood vessels from calcification."

Hardening and narrowing of the arteries rarely causes a clear warning at first. That makes claims that a vitamin can ‘clear’ calcified blood vessels understandably tempting, particularly when vitamin K2 and vitamin D3 combinations are easy to buy online and on the high street.

Vitamin K does help activate proteins involved in how the body handles calcium. But this does not mean a supplement can reverse atherosclerosis, prevent a heart attack or replace treatment for raised blood pressure or cholesterol. The practical message is less dramatic: eat a varied diet that provides vitamin K, be careful with supplements, and concentrate on the proven ways to reduce cardiovascular risk.

Vitamin K is important for normal body functions, but it is not a shortcut for undoing established artery disease.

What people mean by ‘calcified arteries’

Arteries can become damaged and narrowed over many years through a process called atherosclerosis. Cholesterol-containing fatty material, inflammatory cells and other substances build up in the artery wall, forming plaques. Calcium can become part of these plaques, making them easier to see on some scans and affecting the flexibility of the vessel.

Calcification is only one element of a much wider process. Smoking, raised LDL cholesterol, high blood pressure, diabetes, inactivity, excess weight, increasing age and family history can all raise the risk of cardiovascular disease. Targeting calcium alone would not address these other factors.

Calcification can also affect heart valves and may occur in people with chronic kidney disease, where mineral balance can be altered. These situations need individual assessment by a clinician, rather than self-treatment with vitamins.

Why vitamin K is relevant

Vitamin K is best known for its role in normal blood clotting. It is also needed to activate several proteins elsewhere in the body. One is matrix Gla protein, often shortened to MGP, which is found in blood vessel walls and other tissues.

Put simply, vitamin K is involved in switching certain proteins into an active form. MGP is thought to play a part in regulating calcium in soft tissues, including blood vessels. Vitamin D has a different role: it helps the body absorb calcium and supports bone health.

This has led to a popular but misleading claim that vitamin D ‘puts calcium in’ while vitamin K ‘sends it to the bones’. The body does not work like a parcel-delivery system. Taking extra vitamin D or vitamin K has not been shown to move calcium out of arteries or reverse plaque.

Vitamin K1 and K2

Vitamin K comes in several forms:

• Vitamin K1, or phylloquinone, is found mainly in green leafy vegetables and plant oils. It is the principal dietary form in a typical UK diet.
• Vitamin K2, or menaquinones, is present in smaller amounts in some animal and fermented foods. Supplements commonly contain a form called MK-7.
• Combined supplements may contain vitamin K alongside vitamin D, calcium or other nutrients. A long ingredient list does not prove that a product is necessary or effective.

Both K1 and K2 contribute to vitamin K activity in the body. Claims that K2 supplements are clearly better than food-based K1 for preventing cardiovascular disease are not established.

What research can and cannot tell us

Research into vitamin K and vascular calcification is continuing. Laboratory research and smaller human studies suggest that vitamin K status may affect proteins linked to calcification. Some trials have investigated whether K2 supplements might slow progression of calcification in particular groups.

However, this is not enough to show that taking K2 prevents heart attacks or strokes, or reverses calcified plaques. Studies have used different doses and forms of vitamin K, involved different groups of people and measured different outcomes over varying lengths of time.

A change in a blood marker or scan measurement is not automatically the same as a meaningful reduction in heart attacks, strokes or deaths. Those questions require large, well-designed trials that follow people over a long period.

A plausible biological mechanism is not the same thing as a proven treatment.

For most people without a diagnosed deficiency, vitamin K is best viewed as one useful nutrient within an overall balanced diet, rather than a treatment for blocked or hardened arteries.

Food sources worth putting on the plate

Vitamin K deficiency is uncommon in healthy adults eating a varied diet. Green vegetables are an easy, dependable source of vitamin K1, and they also provide fibre and a range of other nutrients.

Useful everyday choices include:

• spinach, kale, spring greens and cabbage;
• broccoli, Brussels sprouts and green beans;
• lettuce, watercress and herbs such as parsley;
• peas and dishes containing leafy greens;
• eggs, cheese and some fermented foods, which may provide smaller amounts of K2.

Fermented soya foods such as natto can contain high amounts of certain forms of K2, but they are not essential to a healthy diet. Tempeh may be a useful food choice, although its vitamin K content can vary. Tofu should not be assumed to provide the same amount.

Keep it practical: stir spinach into a curry or omelette, serve broccoli with a roast, add watercress to sandwiches, or keep frozen greens for quick weekday meals.

Vitamin D, calcium and the UK winter

Vitamin D is frequently sold with K2 because both nutrients are associated with bone health. UK public health advice is that everyone should consider taking a daily supplement containing 10 micrograms of vitamin D during autumn and winter, when sunlight is not strong enough for reliable vitamin D production in the skin.

Some people may be advised to take vitamin D throughout the year, including people who spend little time outdoors, cover most of their skin when outside, or have darker skin. A pharmacist, GP or other healthcare professional can help if you are unsure what applies to you.

That does not mean everybody needs a combined D3 and K2 product. High-dose vitamin D or calcium should not be taken without advice, particularly if you have kidney disease, a history of kidney stones, high calcium levels or certain hormonal conditions.

If you have been advised to take calcium or vitamin D for bone health, do not stop prescribed treatment because of online claims about calcification. Ask your prescriber or pharmacist how it fits your own circumstances.

The crucial warning about warfarin

Vitamin K can interfere with warfarin, an anticoagulant that works by reducing vitamin K activity. Starting a vitamin K supplement, or making sudden large changes to the amount of vitamin K in your diet, can alter warfarin’s effect.

If you take warfarin

1. Do not start K1 or K2 supplements before speaking to your anticoagulation clinic, GP or pharmacist.
2. Do not cut out green vegetables altogether. A consistent eating pattern is generally safer than large day-to-day changes.
3. Tell healthcare professionals about every supplement you use, including multivitamins, bone-health products and ‘heart health’ blends.
4. Follow your INR monitoring plan and seek advice if your diet changes substantially.

Other anticoagulants, including apixaban and rivaroxaban, work differently from warfarin. Even so, it is sensible to check any new supplement with a pharmacist or prescriber. ‘Natural’ does not automatically mean harmless.

Common mistakes to avoid

• Expecting a capsule to dissolve plaque. There is no reliable evidence that vitamin K2 reverses established atherosclerosis.
• Trying to interpret a scan result alone. Coronary artery calcium scores and other vascular scans need to be considered alongside your wider health and risk factors.
• Taking large doses because K2 is paired with D3. Combination packaging is not proof that more is better.
• Overlooking medicine interactions. Warfarin is particularly important, but all supplements should be declared to your clinician or pharmacist.
• Focusing on vitamins while ignoring smoking, blood pressure or cholesterol. These have a much stronger evidence base in reducing cardiovascular risk.
• Assuming no symptoms means no risk. Raised blood pressure and cholesterol often cause no noticeable symptoms.

The actions that matter most

There is no single food or vitamin that guarantees healthy blood vessels. The most useful approach is to address the established drivers of atherosclerosis.

Consider the following:

• do not smoke, and use NHS stop-smoking support if needed;
• build regular movement into the week, whether that is brisk walking, cycling, swimming or gardening;
• base meals around vegetables, fruit, pulses, wholegrains, nuts and unsalted foods, with oily fish where suitable;
• limit foods high in saturated fat, salt and added sugar;
• have your blood pressure checked and attend relevant NHS health checks or screening invitations;
• discuss raised cholesterol, diabetes risk or a strong family history of early heart disease with a healthcare professional;
• take prescribed medicines as directed rather than replacing them with supplements.

Seek urgent help by calling 999 if you have severe or persistent chest pain, sudden breathlessness, or symptoms of a stroke such as facial drooping, arm weakness or speech difficulty.

Vitamin K has a worthwhile place in a balanced diet because the body needs it. For most people, ordinary food - especially green vegetables - is the sensible route. Treat K2 capsules as something to discuss with a pharmacist or clinician, not as a proven defence against calcified arteries.