In brief. Vitamin D3 and K2 are two fat-soluble vitamins that are often sold together because both are involved in how the body handles calcium and in maintaining normal bones. Under EU law, vitamin D contributes to the normal absorption and utilisation of calcium and phosphorus, normal blood calcium levels, the maintenance of normal bones, teeth, and muscle function, the normal function of the immune system, and has a role in the process of cell division. Vitamin K contributes to normal blood clotting and the maintenance of normal bones. This guide explains what they are and why they are combined. This is information, not medical advice.
What are vitamin D3 and K2?
Vitamin D3 (cholecalciferol) is the form of vitamin D that the skin produces from sunlight and the form most commonly used in supplements. Vitamin K2 is one of the two main types of vitamin K (the other is K1, found mainly in leafy vegetables); K2 occurs in fermented foods and some animal products. Both are fat-soluble, which means the body stores them and they are absorbed most effectively with a meal that contains some fat.
Why are vitamin D3 and K2 combined?
They are combined because both are involved in how the body manages calcium and in maintaining normal bones. Under EU law, vitamin D contributes to the normal absorption and utilisation of calcium, normal blood calcium levels, and the maintenance of normal bones, while vitamin K contributes to the maintenance of normal bones. Combining the two is therefore a logical convenience: it puts two fat-soluble vitamins associated with bones into one daily dose. This is a description of their role in the body, not a promise of a specific result.
What can legally be said about each vitamin?
In the EU, only health claims authorised under Regulation (EC) No 1924/2006 may be used. The authorised claims are precise, and nothing beyond them may be implied.
| Vitamin | Authorised EU claims (what it contributes to) |
|---|---|
| Vitamin D | Normal absorption and utilisation of calcium and phosphorus; normal blood calcium levels; maintenance of normal bones, teeth, and muscle function; normal function of the immune system; a role in the process of cell division. |
| Vitamin K | Normal blood clotting; maintenance of normal bones. |
Note one thing this article will not do: it will not make any claim about the heart, arteries, or counteracting calcification. There is no authorised EU health claim of that kind for vitamin K2, so a responsible brand does not suggest one. The authorised territory for these two vitamins is bones, plus calcium handling, muscle function, immune function, and cell division for vitamin D, and blood clotting for vitamin K. Nothing more.
What is MK-7, and why is it used?
Vitamin K2 includes several subtypes called menaquinones, written as MK-n. The two most commonly discussed in supplements are MK-4 and MK-7. MK-7 is popular in supplements because it has a longer half-life in the blood than MK-4, so it remains available for longer after a single daily dose; this is a pharmacokinetic property reported in peer-reviewed research (study), not a health claim. MK-7 is often produced through fermentation. When a label names a K2 form, it is usually MK-7.
How to choose a vitamin D3 and K2 supplement
- Clear amounts on the label. The amount of vitamin D, in micrograms and often also shown in International Units, and the amount of vitamin K2 should be clearly stated rather than hidden in a blend.
- A named K2 form. Look for the type of menaquinone, usually MK-7, rather than just the words vitamin K2.
- An appropriate amount of vitamin D for you. More is not automatically better with a fat-soluble vitamin. If you do not know your level, a blood test and a professional can help determine the amount.
- Drops or capsules with some fat. Because both vitamins are fat-soluble, an oil base or taking them with a meal aids absorption.
For our own formula and the form of K2 we use, see our vitamin D3 and K2 drops.
Is it safe? What you need to know
Vitamin D is fat-soluble, so the body stores it, and very high intakes can build up over time and cause harm. Do not take megadoses, and stay within the amount on the label or the amount advised by a professional. Vitamin K also matters here: because vitamin K contributes to normal blood clotting, it can interact with anticoagulant medicines (blood thinners) such as warfarin. If you take a blood thinner, are pregnant or breastfeeding, have kidney problems, or have a condition that affects calcium, speak to a doctor or pharmacist before taking a D3 and K2 supplement. Supplements are not a substitute for medical care.
Frequently asked questions
Why take vitamin D3 and K2 together?
Both are fat-soluble vitamins involved in how the body handles calcium and in maintaining normal bones, so they are often combined in one daily dose. That is a description of their role, not a promise of a result.
Does the combination help the heart or arteries?
There is no authorised EU health claim linking vitamin K2 to the heart, arteries, or calcification, so we do not make that claim. The authorised claims concern bones, calcium handling, muscle and immune function, and blood clotting, as stated above.
What is the difference between K1 and K2?
K1 (phylloquinone) is found mainly in leafy vegetables; K2 (menaquinones, such as MK-7) occurs in fermented foods and some animal products. The EU claims for normal blood clotting and the maintenance of normal bones apply to vitamin K in general.
Should I take it with food?
Both vitamins are fat-soluble, so taking them with a meal containing some fat, or using oil-based drops, supports absorption.
Can I take it with a blood thinner?
Not without medical advice. Because vitamin K contributes to normal blood clotting, it can interact with anticoagulant medicines. Speak to your doctor or pharmacist first.
Sources
- EU Register of nutrition and health claims made on foods (authorised claims for vitamin D and vitamin K). ec.europa.eu/food/safety/labelling-and-nutrition/nutrition-and-health-claims
- Regulation (EC) No 1924/2006 of the European Parliament and of the Council on nutrition and health claims made on foods.
- EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific opinions on the substantiation of health claims related to vitamin D and vitamin K. EFSA Journal.
- Schurgers LJ, Teunissen KJF, Hamulyak K, et al. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7 (MK-7). Blood. 2007;109(8):3279-3283. (Reports the longer half-life of MK-7.) PubMed
Written by the NOTFORTOMORROW editorial team. How we research: we base factual statements on the EU Register of health claims and peer-reviewed literature, cite our sources, and date our reviews. This article is for information, not medical advice; speak to a qualified professional about your situation, especially if you take a blood thinner. Last reviewed: 2026-06-06.
