Vitamin K2: What It Does, How to Take It and What to Combine It With
Vitamin K2 is often sold together with vitamin D3. However, many people don't know how K2 differs from K1, or whether they need it at all.
In this article, you will learn what vitamin K is needed for and where to get it. We also cover what studies show about bones and when to discuss a K2 supplement with your doctor.
In brief. Vitamin K contributes to normal blood clotting and to the maintenance of normal bones.1 An intake of about 70 µg of vitamin K per day is adequate for adults.2 If you take warfarin or a similar medicine, only take a vitamin K supplement after talking to your doctor.3
How do vitamins K1 and K2 differ?
| Form | Where it is found | Worth knowing |
|---|---|---|
| K1 (phylloquinone) | Green leafy vegetables: spinach, cabbage, broccoli3 | Most of the vitamin K we get from food is K1. |
| K2 (menaquinones, e.g. MK-4, MK-7) | Fermented foods, cheese, eggs, meat3 | MK-7 stays in the body longer than K1.4 |
The richest source of K2 is natto, a Japanese dish made from fermented soya beans. In Europe, much of our K2 comes from cheese and other dairy and meat products.4
What is vitamin K needed for?
Vitamin K contributes to:1
- normal blood clotting;
- the maintenance of normal bones.
These claims apply to vitamin K in general, whether it is K1 or K2.
How much vitamin K do you need per day?
For adults, about 1 µg of vitamin K per kilogram of body weight per day is adequate, i.e. around 70 µg.2 No tolerable upper intake level has been set for vitamin K, as there are insufficient data on adverse effects.5
Example. On EU labels, the % RI (reference intake) for vitamin K is calculated from 75 µg.6 So a 100 µg K2 capsule should show 133% RI. If you see 83%, it has been calculated using the US reference value.
What do studies show about bones?
One study included 244 healthy postmenopausal women. They took 180 µg of MK-7 or a placebo every day for 3 years. In the MK-7 group, the age-related decline in bone density at the lumbar spine and femoral neck was smaller.7
What this means for you. This is a single study in a specific group of people. Calcium, vitamin D, protein and physical activity remain the most important factors for bones.
Why is K2 combined with vitamin D3?
Both vitamins contribute to the maintenance of normal bones, and vitamin D also contributes to normal absorption of calcium.1 This is why they are often found in a single product. You can also take them separately.
Vitamin K is fat-soluble, so it is convenient to take it with a meal.3
When should you be careful?
- Warfarin and similar medicines. Vitamin K can reduce their effect. The key is not to avoid vitamin K but to get a consistent amount of it. Discuss any supplement containing vitamin K with your doctor.3
- Other medicines. Some antibiotics and cholesterol-lowering medicines can affect vitamin K levels.3 Ask your pharmacist.
- Multivitamins. Check whether any other products you take also contain vitamin K.
Selected vitamin K2 products
Commercial information. The products listed here are available in our shop. This is not a ranking of effectiveness. Before buying, check the ingredients and directions for use on the product page.
MK-7 Vitamin K-2, 100mcg - 60 vcaps - NOW Foods
Vitamin K2 in the MK-7 form, 100 µg per capsule. Take 1 capsule a day with a meal. The capsules are made from plant cellulose.8
Natural Vitamin K2 MK7 with MenaQ7, 45mcg - 180 vcaps - Doctor's Best
Vitamin K2 in the MK-7 form, 45 µg per capsule. Take 1 capsule a day with a meal. This lower dose is convenient if you also get vitamin K from food.9
Vitamin K2 MK-7, 100mcg - 60 softgels - Osavi
Vitamin K2 in the MK-7 form, 100 µg per softgel. Take 1 softgel a day with a meal. The manufacturer recommends taking it with food.10
Vitamin D3 + K2, 2000IU + 100mcg - 60 softgels - Osavi
Each softgel contains 50 µg (2,000 IU) of vitamin D3 and 100 µg of vitamin K2 MK-7. Take 1 softgel a day. If you also take a separate vitamin D supplement, add up the total amount.11
Frequently asked questions
Do I need K2 if I take vitamin D?
Not necessarily. If you eat a varied diet that includes cheese, eggs and green vegetables, you usually get enough vitamin K. The combination is convenient but not essential.
Can you overdose on vitamin K2?
No adverse effects have been identified at usual doses.5 Even so, stick to the dose recommended by the manufacturer.
What is the difference between MK-4 and MK-7?
These are two forms of K2. MK-7 stays in the body longer. That is why supplements usually contain MK-7 in micrograms, but MK-4 in milligrams.4
Scientific sources
- Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods (consolidated version). EUR-Lex
- EFSA NDA Panel. Dietary reference values for vitamin K. EFSA Journal. 2017;15(5):4780. doi:10.2903/j.efsa.2017.4780
- NIH Office of Dietary Supplements. Vitamin K – Fact Sheet for Health Professionals. ods.od.nih.gov
- Linus Pauling Institute, Oregon State University. Vitamin K. Micronutrient Information Center. lpi.oregonstate.edu
- Scientific Committee on Food, EFSA. Tolerable upper intake levels for vitamins and minerals. 2006. efsa.europa.eu
- Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex XIII. EUR-Lex
- Knapen MHJ, Drummen NE, Smit E et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013;24(9):2499–2507. doi:10.1007/s00198-013-2325-6
- NOW Foods. MK-7 Vitamin K-2, 100 mcg, 60 capsules. Product label.
- Doctor's Best. Natural Vitamin K2 MK7 with MenaQ7, 45 mcg, 180 capsules. Product label.
- Osavi. Vitamin K2 MK-7, 100 mcg, 60 capsules. Product label.
- Osavi. Vitamin D3 + K2, 2000 IU + 100 mcg, 60 capsules. Product label.
Disclaimer. This article is for information only and does not replace advice from a doctor or pharmacist. Food supplements are not intended to treat or prevent disease and do not replace a varied diet and a healthy lifestyle. Consult a healthcare professional before taking supplements. This is especially important if you are pregnant or breastfeeding, have a chronic condition or take medication.
