Health Reference Library

Do you need to take K2 with vitamin D3?

This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.

Summary

No, vitamin D3 works on its own; the NHS 10 microgram autumn and winter advice says nothing about K2. The case for K2 is about where calcium ends up: vitamin D increases the calcium you absorb, and vitamin K activates the proteins that bind it into bone and keep it out of artery walls. The three year Dutch trial of MK-7 at 180 micrograms a day found less bone loss and less arterial stiffness in postmenopausal women; the 2022 Danish trial found it did not slow existing heart valve calcification. So K2 is a reasonable addition at higher or long term vitamin D doses, not a requirement. Anyone on anything that affects clotting must ask their GP first.

How it works

Vitamin D raises the amount of calcium absorbed from food. Two proteins decide what happens to it: osteocalcin, which binds calcium into the bone matrix, and matrix Gla protein, which stops calcium settling in blood vessel walls and cartilage. Both proteins only work once vitamin K has activated them. MK-7, the form of K2 from fermented soya, stays in the blood for about three days, so a single daily dose keeps both proteins switched on; MK-4 lasts hours. The logic of the pair is that more calcium in should come with more calcium correctly placed.

Effective dose

Vitamin D: 10 micrograms (400 IU) a day is the NHS standard, with a ceiling of 100 micrograms (4000 IU) a day unless a GP directs otherwise. Vitamin K: the UK reference intake is 1 microgram per kilogram of body weight a day, about 70 micrograms for an adult, from all sources. The MK-7 trials used 180 micrograms a day for three years, and 360 micrograms in the arterial stiffness trial; 100 to 200 micrograms is the usual supplement range.

Timing

Both are fat soluble, so take them with the meal that contains the most fat, together or apart. Combined products exist because the two share the same timing; there is no absorption reason to keep them separate.

Safety profile

Vitamin K itself has no upper limit and no toxicity at supplement doses in healthy people. The one hard rule: vitamin K acts on the clotting system, so anyone taking anything that affects blood clotting, or with a clotting disorder, must check with their GP or pharmacist before starting K2. Vitamin D above 100 micrograms a day for months can raise blood calcium.

Interactions

Vitamin D increases calcium absorption; K2 directs it. Magnesium is a cofactor for activating vitamin D and for the enzymes that use vitamin K. Vitamin E in very large doses can interfere with vitamin K.

Guideline positions

NHS: vitamin D 10 micrograms a day in autumn and winter, ceiling 100 micrograms. NIH Office of Dietary Supplements: vitamin K fact sheet. Three year low dose MK-7 supplementation and bone loss in postmenopausal women (2013). MK-7 supplementation improves arterial stiffness in postmenopausal women (2015). Vitamin K2 and D in patients with aortic valve calcification, randomised trial (2022).

Practical framework

If you take 10 micrograms of vitamin D through the winter, K2 is optional. If you take vitamin D year round at 50 micrograms or more, or you are past the menopause, adding MK-7 is reasonable. Nutri Tailor stocks [vitamin D3 and K2 capsules](/products/vitamin-d3-k2), 2500 IU of D3 with 200 mcg of K2 per capsule; [vitamin D3 and K2 oil](/products/vitamin-d3-k2-oil), 1000 IU with 50 mcg of K2 per ten drops for flexible dosing; and vitamin K2 MK-7 on its own at 150 mcg per capsule, all made in the UK. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.

Common misconceptions

That vitamin D without K2 is dangerous: at ordinary doses it is the NHS standard. That K2 clears existing calcium from arteries: the 2022 trial found it did not reverse calcification already there. That K1 from greens does the same job: K1 goes mostly to the liver for clotting; MK-7 reaches bone and vessels.

Sources

  1. NIH Office of Dietary Supplements 2021. Vitamin K Fact Sheet for Health Professionals. NIH ODS.
  2. Knapen MH et al 2013. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int 24:2499-507.
  3. Knapen MHJ, Braam LAJLM, Drummen NE, Bekers O, Hoeks APG, Vermeer C 2015. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women: A double-blind randomised clinical trial. Thrombosis and Haemostasis. PMID: 25694037 · DOI: 10.1160/th14-08-0675
  4. Diederichsen ACP, Lindholt JS, Möller S, Øvrehus KA, Auscher S, Lambrechtsen J, Hosbond SE, Alan DH, Urbonaviciene G, Becker SW, Fredgart MH, Hasific S, Folkestad L, Gerke O, Rasmussen LM, Møller JE, Mickley H, Dahl JS 2022. Vitamin K2 and D in Patients With Aortic Valve Calcification: A Randomized Double-Blinded Clinical Trial (AVADEC). Circulation. PMID: 35465686 · DOI: 10.1161/circulationaha.121.057008
  5. NIH Office of Dietary Supplements 2025. Vitamin D: Fact Sheet for Health Professionals. National Institutes of Health, Office of Dietary Supplements.

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