Often overlooked in favour of vitamins C and D, vitamin K plays a fundamental role in the body. This fat-soluble nutrient helps activate proteins involved in blood clotting and also acts in calcium metabolism — contributing to bone maintenance and blood vessel health.

A study published in the Proceedings of the National Academy of Sciences placed vitamin K among the nutrients investigated for its possible role in maintaining health as we age. However, this relationship does not mean that increasing vitamin K intake alone is capable of prolonging life.

The types of vitamin K

Vitamin K appears mainly in two natural forms:

• K1 (phylloquinone) — found primarily in green leafy vegetables such as kale, lettuce, broccoli, and asparagus.

• K2 (menaquinone) — produced by healthy bacteria in the gut and also found in animal-based foods like milk, liver, and fermented products. This type is usually more easily absorbed by the body and has a longer lifespan in the bloodstream.

There is also K3 (menadione), a synthetic form.

Helps control calcium

One of the main roles of vitamin K is in blood clotting. The liver depends on the nutrient to produce proteins involved in this process — including prothrombin and other clotting factors.

Vitamin K also acts to regulate calcium deposition in the body. In bones, it helps fix the mineral. In blood vessels, it participates in mechanisms that limit inappropriate deposition, protecting the cardiovascular system as a whole.

How much to consume?

Recommendations vary by reference:

Since vitamin K is present in foods from different groups, a balanced and varied diet is generally enough to reach the recommended daily amounts.

When can deficiency occur?

Vitamin K deficiency is uncommon in healthy adults. When it does occur, the main sign is difficulty with blood clotting — with increased tendency to bleed and even haemorrhage.

Conditions that impair intestinal absorption can increase deficiency risk, including:

• Gastrointestinal diseases (e.g., irritable bowel syndrome, Crohn's disease)

• Bariatric surgery

• Certain prolonged antibiotic treatments

Newborns also present a particular condition. Since they are born with small reserves of the nutrient and their gut microbiota is still developing, they may develop deficiency and bleeding. For this reason, vitamin K is routinely administered intramuscularly to newborns shortly after birth.

What about supplements?

The presence of vitamin K in a wide range of foods makes diet the main source for healthy individuals. Supplements are reserved for specific situations, evaluated by healthcare professionals through clinical and laboratory assessments.

In excess, the nutrient can increase the risk of blood clots, thrombosis, jaundice, and liver dysfunction.

Therefore, suspected deficiency should not be treated on your own. Medical evaluation considers symptoms, history, and — when necessary — tests to determine whether supplementation is truly needed.

Key takeaway

Vitamin K may be less talked about than C and D, but it plays essential roles in blood clotting, bone health, and cardiovascular protection. A varied diet rich in green vegetables and fermented foods typically provides adequate amounts for healthy adults. If you suspect deficiency, seek professional guidance rather than self-supplementing.