Vitamin D3 with K2
Vitamin D helps your body absorb calcium, and your skin makes it from sunlight. K2 is often paired with it on the theory that it steers calcium into bones rather than arteries. One trial found no effect on heart-valve calcium; a newer one found slower calcium buildup in the heart's arteries on scans, but it's not known whether that prevents heart attacks.
Vitamin D is a fat-soluble vitamin that the body also makes when the sun's UV rays hit the skin. It helps the gut absorb calcium and has other roles, including in immune function and reducing inflammation. Most evidence shows D3 raises blood vitamin D levels more than the other form, D2. It's often sold with vitamin K2 on the theory that K2 steers calcium into bone rather than arteries. A 2022 trial (AVADEC) found no significant effect on heart-valve calcification; a 2026 trial (DANCODE), in people with heavy coronary calcium, found it slowed calcium buildup in the heart's arteries on scans. Neither trial showed that it prevents heart attacks.
Research & evidence
Strong support Some support Weak or no supportColours show how well the sources back each point. The reason is next to each one.
Prolonged vitamin D deficiency is linked to weakened bone (osteomalacia in adults, rickets in children), and clinical trials show vitamin D combined with calcium supplementation may increase bone mineral density in postmenopausal women and older men specifically — though it remains unclear whether this translates into fewer falls or fractures.
Moderate evidenceSome support. Shown only in certain groups, uses, strains or doses
Study details
The current NIH ODS Vitamin D fact sheet (June 2025) says the bone-density benefit is for vitamin D and calcium taken together, in postmenopausal women and older men — not vitamin D alone, and not specifically in people who are deficient. It gives no effect size, and adds: "it is not clear whether they reduce falls and fracture rates."
Source: NIH Office of Dietary Supplements, Vitamin D — Health Professional Fact Sheet, "Bone health and osteoporosis" section (page last updated June 27, 2025). View source
Vitamin D plays a modulatory role in immune function, and low levels are associated with higher susceptibility to respiratory infections. The protective effect of supplementation is modest in absolute terms — one major meta-analysis found roughly a 2-percentage-point absolute reduction (42% to 40%) pooled across a broad, somewhat inconsistent mix of infection types, with benefit concentrated in people who were already significantly deficient and using daily/weekly (not occasional high-dose) supplementation.
Moderate evidenceSome support. Shown only in certain groups, uses, strains or doses
Study details
Martineau et al. 2017 (BMJ; individual-participant-data meta-analysis of 25 RCTs, 10,933 participants; rated high quality by the authors using GRADE): OR 0.88 (95% CI 0.81-0.96, p=0.003) for reducing the risk of at least one acute respiratory infection. The benefit was concentrated in people with baseline 25(OH)D below 25 nmol/L (OR 0.58) and was not significant in less-deficient participants (OR 0.89); bolus-only dosing showed no benefit. An editorial in the same BMJ issue (Bolland & Avenell 2017) noted that the absolute risk reduction was only about 2 percentage points and that the infection definition pooled very different conditions (self-reported colds through confirmed pneumonia), and concluded the evidence doesn't yet support routine supplementation to prevent respiratory infections.
Source: Martineau AR, Jolliffe DA, Hooper RL, et al. "Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data." BMJ. 2017;356:i6583; companion editorial: Bolland MJ, Avenell A. BMJ. 2017;356:j456. View source
A 2022 randomized controlled trial (AVADEC, n=365 men with pre-existing aortic valve calcification) found no significant effect of K2+D3 vs. placebo over 2 years on valve calcification; it rose slightly less with K2+D3 than with placebo, but the difference was well within chance. The authors concluded the combination "is not effective in the prevention of AVC progression."
Not supported by current evidenceWeak or no support. Trials found no clear benefit
Study details
AVADEC (Diederichsen et al., Circulation 2022; 365 men aged 65-74, all with substantial aortic valve calcification; MK-7 720mcg/day + D3 25mcg/day vs. placebo for 24 months). Primary endpoint, aortic valve calcification progression: scores rose 275 AU on K2+D vs. 292 AU on placebo, a difference of -17 AU (95% CI -86 to 53, p=0.64). Authors' conclusion: "the combination of MK-7 and vitamin D is not effective in the prevention of AVC progression." Secondary results for aortic and coronary artery calcification were also not significantly different. The trial gave 25mcg (1,000 IU) of D3 with 720mcg of K2, in people who already had significant calcification, so it doesn't directly test whether K2 protects against calcium buildup linked to high-dose D3.
Source: Diederichsen A, et al. (AVADEC trial). "Vitamin K2 and D in Patients With Aortic Valve Calcification: A Randomized Double-Blinded Clinical Trial." Circulation. 2022 May 3;145(18):1387-1397. View source
In people with heavy coronary artery calcium, two years of vitamin K2 (720 µg a day) plus D3 (25 µg a day) slowed the buildup of calcium in the heart's arteries on CT scans: it rose an average of 196 AU vs 248 AU on placebo (DANCODE, 2026). This is a scan measure — the trial's abstract doesn't report heart attacks or other heart events.
Limited evidenceSome support. Based mainly on one review or trial
Study details
DANCODE (Circulation 2026; 398 participants with CAC ≥400, 30% women, median age 71; 720 µg K2 + 25 µg D3 or placebo for 24 months). Primary end point, change in CAC score at 24 months: mean CAC rose 196 AU (95% CI 178–214) on K2+D3 vs 248 AU (95% CI 225–271) on placebo, a between-group difference of −52 AU (95% CI −79 to −24); the effect was consistent across sex and baseline CAC subgroups. In the 143 participants who had CT angiography, total plaque volume rose similarly in both groups, non-calcified plaque didn't change between groups, and calcified plaque grew less on K2+D3 (−8 mm³, 95% CI −13 to −2). The trial's published protocol (BMJ Open 2023, NCT05500443) named CAC progression at 2 years as the primary outcome, and states: "Study tablets, including placebo, are provided free of charge by Kappa Bioscience, Norway and Orkla Care, Denmark." Supporting evidence for K2 alone (without D3): VitaK-CAC (JAMA Cardiology 2026; 180 people with CAC 50–400; MK-7 360 µg a day vs placebo for 2 years) found median CAC rose 145 → 214 AU on placebo vs 135 → 184 AU on MK-7 (P = .02).
Source: DANCODE trial. Circulation. 2026 (PubMed 42661461); protocol: Hasific S, … Diederichsen A. BMJ Open. 2023;13(7):e073233 (NCT05500443); Vossen LM, … Kroon AA. "Two Years of Menaquinone-7 Supplementation and Coronary Artery Calcification: A Randomized Clinical Trial." JAMA Cardiol. 2026;11(8):719-726. View source
Dosage
| Form | Amount |
|---|---|
| Any form | Recommended daily amount of vitamin D for adults: 600 IU (15 mcg) through age 70, and 800 IU (20 mcg) over 70. The upper limit for adults is 4,000 IU (100 mcg) a day. NIH's adequate intake for vitamin K (all forms) is 120 mcg a day for men and 90 mcg for women. Supplements contain K2 as MK-4 or MK-7. |
Side effects
Well documented Reported (case reports, anecdotal or one study) None reportedThe circle shows how well documented an effect is, not how serious it is. A rarely reported effect can still be serious, so always read ‘When to stop’.
| Effect | Frequency | When to stop |
|---|---|---|
| Vomiting, stomach pain, high calcium in the blood or urine, kidney stonesWell documentedListed plainly by NIH, MSK or LiverTox | Not stated | Stop and see a doctor if any of these happen. |
Safety & interactions
Safety
Too much vitamin D can be harmful. The upper limit for adults is 4,000 IU (100 mcg) a day. Vitamin D toxicity can raise blood calcium (hypercalcemia), which can cause nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, passing large amounts of urine, excessive thirst, and kidney stones. It almost always comes from too much vitamin D from supplements, not from sun exposure. No harmful effects have been reported from vitamin K in food or supplements, and there is no upper limit for it.
Contraindications
Talk to your healthcare provider before taking vitamin D if you have kidney stones, kidney disease, high blood calcium, heart disease, or liver disease. MSK's professional summary also lists gastrointestinal disease and other conditions that affect calcium metabolism. If you take warfarin or a similar blood thinner, the vitamin K2 in this combination can change how well it works — see Drug interactions.
Drug interactions
Vitamin K (including K2 from supplements) can seriously interact with warfarin and other vitamin K antagonists (such as acenocoumarol and phenprocoumon). Sudden changes in intake can increase or decrease the anticoagulant effect (NIH ODS). The warfarin prescribing label is consistent with this: it lists increased vitamin K intake as a cause of reduced INR response and tells patients to keep vitamin K intake consistent. This is specifically about vitamin K antagonists — it does not apply to DOACs like apixaban (Eliquis) or rivaroxaban (Xarelto), which don't work through vitamin K. Anyone on warfarin should talk to their prescriber before starting a K2-containing supplement.
Thiazide diuretics (such as hydrochlorothiazide, indapamide, and chlorthalidone) reduce calcium excretion, and vitamin D increases calcium absorption. Together they can raise blood calcium too high, especially in older adults and people with kidney problems or hyperparathyroidism (NIH ODS). MSK also lists this interaction.
Corticosteroids such as prednisone can lower vitamin D levels. They impair vitamin D metabolism and reduce calcium absorption (NIH ODS). In national survey data (NHANES 2001-2006), vitamin D deficiency was about twice as common among oral steroid users (11%) versus non-users (5%). MSK also lists chronic steroid use as a risk factor for low vitamin D.
Established: stated plainly by an authoritative source. Documented: supported by case reports or trial data. Theoretical: based on mechanism, animal data, or a cautious listing. Always check with your pharmacist or prescriber.
Which form to buy
Vitamin D3 (cholecalciferol)
Good choiceRaises blood levels more than other forms (per NIH)
Most evidence indicates D3 raises blood vitamin D levels more than D2, and keeps them higher for longer. Both forms are well absorbed.
Vitamin D2 (ergocalciferol)
Works, with a catchWorks, but raises blood levels less than the leading form
Also raises vitamin D levels, but most evidence indicates less than D3.