The Vitamin K Guide

Here is the complete guide to vitamin K, a vitamin that is often overlooked but absolutely vital, particularly abundant in the plant kingdom for those who consume green vegetables.

The complete guide to vitamin K: the secret of blood clotting and bone strength

Vitamin K gets its name from the German word Koagulation. It is famous for its role in stopping bleeding, but its functions go far beyond that: it is the essential partner of calcium and vitamin D in maintaining strong bones.

There are two main forms: vitamin K1 (phylloquinone), which is abundant in plants, and vitamin K2 (menaquinones), produced by bacteria. For vegetarians and vegans, vitamin K is generally easy to obtain, provided that you include plenty of “green” foods on your plate. Here is how to optimize your intake.

What does vitamin K actually do in your body?

Vitamin K acts as a biological switch that activates specific proteins:

  • Blood clotting: It activates clotting factors that allow blood to thicken and form a scab when a cut occurs. Without it, even a minor injury could cause hemorrhaging.

  • Bone health: It activates osteocalcin, a protein that helps bind calcium into the bone structure. Without vitamin K, calcium remains in the bloodstream instead of strengthening your bones.

  • Cardiovascular protection: It helps prevent calcium from depositing in the walls of your arteries (arterial calcification). By “cleaning” calcium from the arteries, it helps prevent heart disease.

  • Cellular metabolism: Recent studies suggest it may also play a role in regulating insulin and inflammation.

 

Nutritional needs: a daily intake is essential

The body stores very little vitamin K. Therefore, it must be consumed every day.

Recommended nutritional intake (RNI)

Profile Recommended daily requirement
Adult man 120 µg
Adult woman 90 µg
Pregnant / breastfeeding woman 90 µg

Did you know? Vitamin K requirements are generally very easy to meet: a single serving of broccoli or kale often provides 2 to 5 times the recommended daily intake!

Understanding the difference between vitamin K1 and K2

For vegans, it is important to understand the origin of these two forms:

  • Vitamin K1 (Phylloquinone): It represents 90% of our intake. It is found in green vegetables. Its main role is related to blood clotting.

  • Vitamin K2 (Menaquinones): It is rarer in the plant world because it is of bacterial origin. It is particularly effective for bone and arterial health. It is found in fermented foods.

Vegan tip: Natto (fermented Japanese soybeans) is the most powerful source of vitamin K2 in the world. For those who dislike its very particular taste, the body can convert a small portion of K1 into K2, and our gut microbiota also produces a small amount.

Top 10 best plant-based sources of vitamin K

Green is the color of vitamin K. The darker the leaf, the more it contains.

Food Serving Vitamin K content (µg)
1. Natto (fermented soybeans) 50 g 450 µg (K2)
2. Kale (cooked) 100 g 800 µg (K1)
3. Spinach (cooked) 100 g 480 µg (K1)
4. Swiss chard (cooked) 100 g 330 µg (K1)
5. Fresh parsley 10 g (a pinch) 160 µg (K1)
6. Broccoli (steamed) 150 g 220 µg (K1)
7. Brussels sprouts 150 g 280 µg (K1)
8. Romaine lettuce 100 g 100 µg (K1)
9. Rapeseed oil 1 tbsp 10 µg (K1)
10. Kiwi 1 medium fruit 40 µg (K1)

Signs of deficiency: bleeding signals

Vitamin K deficiency is rare in healthy adults, but it can occur after prolonged antibiotic use (which destroys gut flora) or in cases of fat malabsorption:

  • Frequent bleeding: Bleeding gums or repeated nosebleeds.

  • Easy bruising: Bruises that appear after minor impacts.

  • Very heavy menstruation: In menstruating women.

  • Bone fragility: Increased risk of fractures over time.

 

FAQ: your common questions about vitamin K

Should vegans supplement vitamin K?

Generally, no. If you eat green vegetables several times a week, your K1 intake is excellent. However, if you take high-dose vitamin D supplements, it is often recommended to take a D3 + K2 complex, as these two vitamins work together to direct calcium toward the bones rather than the arteries.

Does cooking destroy vitamin K?

No, vitamin K is very resistant to heat. On the contrary, as with vitamin A, cooking green vegetables reduces their volume and breaks down fibers, which allows you to absorb more of it.

Are there medication interactions?

Warning! If you take anticoagulant medications (such as Warfarin or vitamin K antagonists), vitamin K may counteract the effect of your treatment. You should not stop eating green vegetables, but maintain a stable intake and consult your doctor before any dietary change or supplementation.

Is vitamin K better absorbed with fat?

Yes, absolutely. Like vitamins A, D and E, it is fat-soluble. For the vitamin K in your spinach or broccoli to cross the intestinal wall, always add a source of fat (olive oil, nuts, avocado) to your meal.

Scientific references and sources

  • ANSES: Nutritional references for vitamin K (Updated 2021).

  • EFSA (European Food Safety Authority): “Scientific Opinion on Dietary Reference Values for vitamin K”.

  • The American Journal of Clinical Nutrition: “Vitamin K intake and bone mineral density”.

  • National Institutes of Health (NIH): Vitamin K Fact Sheet for Health Professionals.

  • Journal of Nutrition and Metabolism: “Vitamin K2, a neglected vitamin in human health”.