The importance of vitamin K for healthy bones

In 1934, it was demonstrated that adding specific food components to the diet resolved the clotting disorders observed in animals, and this effect was linked to a previously unknown vitamin. Vitamin K was initially described precisely as a component essential for normal blood clotting, but subsequent research showed that it also plays a role in bone metabolism. The discovery of vitamin K was awarded the Nobel Prize in Physiology or Medicine for 1943.

1. Characteristics of vitamin K
2. Sources of vitamin K
3. Absorption of vitamin K
4. Vitamin K and bones
5. Vitamin K requirements
6. FAQ – Vitamin K and healthy bones

Characteristics of vitamin K

Vitamin K is a group of fat-soluble compounds, not a single substance. It is not a mineral that builds bone and does not provide calcium on its own. However, it enables certain proteins in the body to function properly. Its primary form found in plant-based foods is vitamin K1, or phylloquinone. Vitamin K2 comprises several menaquinones, designated by the symbols MK-4 to MK-13, which differ in structure, dietary sources and duration of retention in the body.

Sources of vitamin K

Vitamin K1 is found primarily in green leafy vegetables, such as kale, spinach, lettuce, Swiss chard, parsley and cabbage. It is also found in broccoli, Brussels sprouts and vegetable oils. Menachinones are found in some fermented foods, particularly natto, and in smaller quantities in certain cheeses, meat, eggs and dairy products. Some menachinones are produced by gut bacteria, although the exact extent to which this production contributes to meeting human requirements has not been established.

Absorption of vitamin K

As vitamin K is fat-soluble, it is absorbed in the small intestine with the help of bile and pancreatic enzymes. The presence of a small amount of fat in a meal can facilitate the utilisation of vitamin K from vegetables. Once absorbed, it is transported via lipoproteins to the liver and other tissues, including bone. Clinically evident deficiency in healthy adults is rare, but the risk may increase in cases of fat malabsorption, biliary tract diseases, following certain gastrointestinal operations, and during treatment with medicines that affect vitamin K metabolism.

Vitamin K and bones

The importance of vitamin K for bones stems primarily from its role in the activation of vitamin K-dependent proteins. Bone tissue is constantly being remodelled: some of its components are removed and replaced by a new matrix, which then undergoes mineralisation. One of the most important bone proteins involved in this process is osteocalcin, produced by osteoblasts – the cells responsible for bone formation. Once properly ‘activated’, osteocalcin can bind calcium more effectively and interact with hydroxyapatite, the main mineral component of bone.

Foods richest in vitamin K

Vitamin K requirements

The European Food Safety Authority has established adequate intake values for vitamin K, as the available data did not allow for the determination of a conventional average requirement. The standards relate primarily to phylloquinone. The adequate intake is 10 µg per day for infants aged 7–11 months, 12 µg for children aged 1–3 years, 20 µg for children aged 4–6 years, 30 µg for children aged 7–10 years, 45 µg for those aged 11–14 years and 65 µg for adolescents aged 15–17 years.

For adults, the figure is 70 µg per day. The same value applies to pregnant and breastfeeding women. The EFSA has not established a tolerable upper intake level for vitamin K due to insufficient data. This standard should not be confused with the reference intake value used on food and supplement labels in the European Union, which is 75 µg.

In healthy individuals, the recommended intake can usually be met through a diet that regularly includes green vegetables and other sources of vitamin K. The main forms used in supplements are phylloquinone, menaquinone-4 and menaquinone-7. Particular caution is required for people taking vitamin K antagonists, such as warfarin, acenocoumarol or phenprocoumon. Sudden changes in the amount of vitamin K obtained from food or supplements can alter the effects of these medicines; therefore, it is important to maintain a consistent intake and to discuss supplementation with a doctor.

"Healthy bones do not depend on a single nutrient. Vitamin K helps to activate proteins involved in the proper metabolism of bone tissue; therefore, its role is best realised as part of a well-balanced diet, rather than as a standalone solution for bone health." Tomasz Maciołek – Physiotherapist

FAQ – Vitamin K and healthy bones

Does vitamin K strengthen bones?

Vitamin K does not build bones directly and is not a source of calcium. According to an approved health claim, it contributes to the maintenance of healthy bones, as it plays a role in the activation of proteins that are important for the normal metabolism of bone tissue.

Is vitamin K alone sufficient to ensure bone health?

No. Bone health is influenced by many factors, including an adequate intake of calcium, vitamin D, protein, regular physical activity and overall diet. Vitamin K is one component of this process.

Which form of vitamin K is better – K1 or K2?

Both forms play important roles in the body. Vitamin K1 is found mainly in green leafy vegetables, whilst K2 is found, amongst other things, in fermented foods and certain animal-derived products. At present, there is no evidence to suggest that, in healthy individuals, supplementation with one form is routinely more beneficial than the other.

Which foods are the best sources of vitamin K?

Green leafy vegetables, such as kale, spinach, Swiss chard, parsley, lettuce, broccoli and Brussels sprouts, provide the highest amounts of vitamin K1. It is a good idea to eat them regularly as part of a varied diet.

Is vitamin K absorbed better when consumed with fat?

Yes. Vitamin K is fat-soluble, so adding a small amount of healthy fat – such as olive oil, rapeseed oil or nuts – can improve its absorption from a meal.

Should everyone take vitamin K supplements?

No. For most healthy people, an adequate amount of vitamin K can be obtained through diet alone. Supplementation is not routinely recommended for everyone and should be based on individual needs.

Can vitamin K interact with medicines?

Yes. People taking anticoagulant medicines that are vitamin K antagonists (e.g. warfarin or acenocoumarol) should not start taking supplements on their own or suddenly change their intake of foods rich in vitamin K without consulting a doctor, as this may affect the effectiveness of their treatment.

Does cooking reduce the vitamin K content in vegetables?

Vitamin K is relatively stable during typical heat treatment. Losses are usually lower than for many water-soluble vitamins, so both raw and cooked vegetables remain a valuable source of it.

Sources:

• Shearer, M. J., Fu, X., & Booth, S. L. (2012). Vitamin K nutrition, metabolism, and requirements: current concepts and future research. Advances in nutrition (Bethesda, Md.), 3(2), 182–195. https://doi.org/10.3945/an.111.001800
• Gundberg, C. M., Lian, J. B., & Booth, S. L. (2012). Vitamin K-dependent carboxylation of osteocalcin: friend or foe?. Advances in nutrition (Bethesda, Md.), 3(2), 149–157. https://doi.org/10.3945/an.112.001834
• Xie, C., Gong, J., Zheng, C., Zhang, J., Gao, J., Tian, C., Guo, X., Dai, S., & Gao, T. (2024). Effects of vitamin K supplementation on bone mineral density at different sites and bone metabolism in the middle-aged and elderly population. Bone & joint research, 13(12), 750–763. https://doi.org/10.1302/2046-3758.1312.BJR-2024-0053.R1