Vitamin K2 and calcium metabolism – how does it support healthy bones?

In 1929, the Danish biochemist Henrik Dam described the observations that led to the discovery of vitamin K, which was initially associated mainly with normal blood clotting. Over time, it was noted that its importance is not limited to this single process, as vitamin K also plays a role in protein metabolism related to bone tissue. According to current scientific knowledge and a health claim approved by the European Union, vitamin K helps maintain healthy bones.

1. Bone structure
2. Vitamin K2 in bones
3. Vitamin K2 in the diet and supplements

Bone structure

Bones are not merely a passive framework of the body, but living tissue that undergoes remodelling throughout a person’s lifetime. Within the bone, the processes of new bone formation and controlled resorption—that is, the removal of older or damaged sections—take place simultaneously. This allows the skeleton to adapt to age, mechanical stress, physical activity, hormonal status and the body’s overall nutritional status. The most mineralised part of the bone is made up of calcium and phosphorus compounds (hydroxyapatite), which give it hardness and resistance to stress, whilst the organic part, including collagen, influences its elasticity and strength.

What matters?

The health of bones depends on the supply of calcium, protein, vitamin D, magnesium, phosphorus and the energy required for continuous tissue renewal. As it turns out, vitamin K is also important, as it plays a role in processes involving proteins present in bone tissue.

Bone abnormalities include, among others, reduced mineralisation and impaired bone remodelling. These conditions include osteopenia (a condition of reduced bone mineral density), osteoporosis (a disease associated with reduced bone strength and an increased risk of fractures), rickets (a disorder of bone mineralisation in children) and osteomalacia (a disorder of bone mineralisation in adults).

Vitamin K2 in bones

Vitamin K2 is discussed in the context of bone health primarily because of its role in the activation of specific proteins. The most important example is osteocalcin, a protein produced by osteoblasts, which are the cells involved in bone formation. Osteocalcin requires a processing step to acquire a form capable of binding calcium within the mineral part of the bone. Vitamin K2 is involved precisely at this stage; therefore, its role is not simply to "direct" calcium to the bones, but to support the proper functioning of bone-building proteins. Even with an adequate supply of this mineral, the body needs mechanisms that enable its utilisation in bone tissue.

European reference values for vitamin K in adults

(set at the level of adequate intake)

Vitamin K2 in the diet and supplements

Vitamin K2 comprises a group of compounds known as menaquinones. They differ mainly in their chemical structure, including the length of the side chain, which influences the compound’s properties. In foodstuffs and supplements, the most commonly discussed are menaquinone-7 (MK-7) and menaquinone-4 (MK-4).

In food

In food, a particularly well-known source of vitamin K2 is natto, i.e. fermented soya (approximately 850–1000 µg of menaquinones per 100 g, mainly MK-7), whilst smaller amounts may be found, amongst other things, in selected mature cheeses (approximately 0.1–94 µg per 100 g, depending on the type of cheese), other dairy products (from a few to several dozen µg/100 g) and animal-derived products (meat usually contains around 0.1–60 µg/100 g, whilst liver and liver products contain even more).

"In some countries, fermented soya, known as natto, is also eaten. Although for many Poles, eating it might be quite a challenge. The fermented soya beans are covered in a sticky substance and give off a distinctive smell. For the Japanese, however, it is a fantastic delicacy and, of course, a source of probiotics." Agata Bugorska – Dietitian

In supplements

In supplements, vitamin K2 is sometimes used on its own or combined with vitamin D, calcium and magnesium. In dietary supplements, vitamin K2 is usually found in microgram doses, most commonly around 25–200 µg per daily serving, depending on the type of preparation and the recommended method of use. Interestingly, vitamin K is also administered to newborns after birth as a preventive measure against bleeding associated with its deficiency; however, this relates to its role in normal blood clotting, rather than supplementation aimed at bone health.

• Tsugawa, N., & Shiraki, M. (2020). Vitamin K Nutrition and Bone Health. Nutrients, 12(7), 1909. https://doi.org/10.3390/nu12071909
• Walther, B., Karl, J. P., Booth, S. L., & Boyaval, P. (2013). Menaquinones, bacteria, and the food supply: the relevance of dairy and fermented food products to vitamin K requirements. Advances in nutrition (Bethesda, Md.), 4(4), 463–473. https://doi.org/10.3945/an.113.003855
• Yan, Q., Zhang, T., O'Connor, C., Barlow, J. W., Walsh, J., Scalabrino, G., Xu, F., & Sheridan, H. (2023). The biological responses of vitamin K2: A comprehensive review. Food science & nutrition, 11(4), 1634–1656. https://doi.org/10.1002/fsn3.3213