Short answer
There is little evidence that taking vitamin D3 and K2 together beats D3 alone. In a 3-year trial of 142 postmenopausal women, adding K2 to vitamin D and calcium did not change bone density. Two Danish trials of the combination on artery and valve calcium gave mixed results, and neither was designed to show fewer heart attacks. If you take warfarin, vitamin K changes matter.
Why people pair them
The idea comes from biology. The NIH Office of Dietary Supplements (ODS) says vitamin K is needed to activate osteocalcin, a bone protein, and that matrix Gla-protein, another vitamin K-dependent protein, might help reduce abnormal calcification in blood vessels.
The step from there to a supplement is mostly a hypothesis. ODS describes the vessel theory as based on animal data, and its fact sheet, last updated in March 2021, says the role of the different forms of vitamin K in arterial calcification and heart disease risk is unclear.
Bone: the trials
The most direct test for women over 50 is a 2021 trial in Osteoporosis International. It gave 142 postmenopausal women with osteopenia 375 mcg of K2 (as MK-7) or placebo for 3 years, and both groups also got vitamin D3 and calcium. Bone density fell at every site in both groups, with no difference between them.
Vitamin D on its own did not prevent fractures in VITAL, a US trial of 25,871 adults. ODS notes that Japan uses a far larger dose of MK-4, 45 mg, as an osteoporosis drug, which is a different situation from a supplement.
Arteries: the trials
Both heart trials were run in Denmark and compared K2 plus vitamin D with placebo. In AVADEC, 365 men with aortic valve calcium took 720 mcg of K2 plus 25 mcg of vitamin D or placebo for 2 years. Valve calcium progressed the same in both groups.
In DANCODE, published August 2026, 398 people with severe coronary calcium took the same combination or placebo for 24 months. Calcium scores rose by 196 units on the combination and 248 on placebo. Neither trial tested K2 against vitamin D alone, and CT calcium scores are not the same as heart attacks or strokes.
Safety: warfarin and the vitamin D limit
ODS calls the interaction between vitamin K and warfarin serious and potentially dangerous. People on warfarin need a consistent vitamin K intake from food and supplements, because sudden changes can raise or lower the drug's effect. If you take warfarin, talk to your prescriber before starting any K2 product.
For vitamin D, the upper limit for adults is 4,000 IU (100 mcg) a day; toxicity can cause high blood calcium. No upper limit was set for vitamin K because of its low potential for toxicity. The adequate intake is 120 mcg for men and 90 mcg for women.
Related questions
Does K2 stop vitamin D from putting calcium in your arteries?
That has not been shown in people. In AVADEC, aortic and coronary calcium scores progressed no differently with K2 plus vitamin D than with placebo.
Is MK-7 different from MK-4?
Both are forms of K2 used in supplements. ODS cites one study finding MK-7 has a longer half-life than vitamin K1.
Do you need K2 if you take vitamin D?
The trials so far do not show it helps bone density. If you are deciding about vitamin D or K for bone health, ask your doctor, especially if you take a blood thinner.
Read next
Sources
- NIH Office of Dietary Supplements: Vitamin K, Fact Sheet for Health Professionals (updated March 2021)
- NIH Office of Dietary Supplements: Vitamin D, Fact Sheet for Health Professionals (updated June 2025)
- Rønn et al., Osteoporosis International: MK-7 on bone mineral density in postmenopausal women with osteopenia, 3-year randomized trial (2021)
- Diederichsen et al., Circulation: Vitamin K2 and D in patients with aortic valve calcification, AVADEC (2022)
- Hasific et al., Circulation: Vitamin K2 and D3 supplementation in patients with severe coronary artery calcification, DANCODE (2026)
Published 2026-10-07 · Last checked 2026-10-07
Educational content, not medical advice. Made for the United States.