Vitamin D3 + K2: What the Research Shows — A Pharmacist's Evidence Review

Dai Tran, PharmD, MBA, B.S.

CEO & Lead Pharmacist, Khang Pharmacy • CA/MN/TX Licensed Pharmacist

Clinical Insights Series • APhA Immunization Certified • 10+ Years Clinical Experience

The Clinical Question

Vitamin D3 is one of the most commonly recommended supplements in modern medicine. Low vitamin D status is more common among people with limited sun exposure and other risk factors, and research links vitamin D status to bone, immune, and cardiovascular health outcomes. A more recent question has emerged: does co-supplementation with Vitamin K2 meaningfully improve outcomes compared to D3 alone?

This article reviews what each nutrient does, what the human clinical evidence supports, and where the evidence is still developing — so you can make an informed decision with your pharmacist or physician.

Vitamin D3: What It Does and What the Evidence Shows

Vitamin D3 (cholecalciferol) is synthesized in the skin on UVB exposure and converted in the liver and kidneys to its active hormonal form, calcitriol. Vitamin D receptors are present on most cell types, giving it broad biological relevance.

Well-established functions:

• Calcium absorption: D3 substantially increases intestinal calcium absorption; deficiency impairs calcium uptake regardless of dietary intake.
• Bone mineralization: Vitamin D is essential for normal bone mineralization. Correcting deficiency is clinically important for prevention of osteomalacia and for bone health in older adults. However, vitamin D supplementation alone has not consistently reduced fractures in generally healthy, vitamin-D-replete adults; benefit appears to depend on baseline deficiency status, calcium status, population, and dosing regimen.
• Immune modulation: Vitamin D receptors are present on immune cells and have a role in innate and adaptive immune responses.

Evidence still developing:

• Associations between low vitamin D and cardiovascular disease, cancer, and mood disorders are well-documented epidemiologically, but large RCTs — including the VITAL trial (PMID: 30415629) — have produced mixed results on whether supplementation reduces these outcomes in populations that are not frankly deficient. Correcting documented deficiency remains clinically important; routine high-dose supplementation in vitamin-D-replete individuals is less clearly supported.

Who Is at Increased Risk for Vitamin D Deficiency?

• People with limited sun exposure or who live in northern latitudes, with risk varying by season, skin pigmentation, clothing, and behavior
• Individuals with darker skin pigmentation
• Adults over 65, as skin synthesis efficiency declines with age
• Individuals with obesity
• Patients with malabsorption conditions such as Crohn’s disease, celiac disease, or post-bariatric surgery
• Patients on medications that affect vitamin D metabolism, including corticosteroids and some anticonvulsants
• Exclusively breastfed infants

A blood test measuring 25(OH)D is the standard way to assess status. Many clinical frameworks use a level below 20 ng/mL as deficiency, but thresholds and treatment targets vary by guideline and clinical context. Supplementation should be individualized rather than treated as a universal dose recommendation.

Vitamin K2: What It Does and What the Evidence Shows

Vitamin K2 (menaquinone) is distinct from Vitamin K1 (phylloquinone), which is primarily involved in coagulation. K2’s main biological role is activating two carboxylation-dependent proteins:

• Osteocalcin: A protein involved in bone matrix formation. K2 is required to carboxylate (activate) osteocalcin, which supports calcium incorporation into bone.
• Matrix Gla Protein (MGP): A protein that inhibits arterial calcification. K2 activates MGP; uncarboxylated MGP has been associated with increased arterial stiffness and calcification in observational research.

D3 increases intestinal calcium absorption, while vitamin K supports carboxylation of osteocalcin and matrix Gla protein. This provides a biological rationale for combined supplementation, but clinical evidence has not established that K2 universally prevents D3-associated soft-tissue calcium deposition.

MK-4 vs. MK-7: Which Form of K2?

• MK-7 (long-chain menaquinone): Derived from natto or fermentation. A human pharmacokinetic study (PMID: 23140417) found that MK-7 reached peak serum concentrations at approximately 6 hours after dosing and remained detectable for up to 48 hours with repeated dosing, whereas nutritional-dose MK-4 was not detectably increased in serum. MK-7 has longer circulating persistence than MK-4 and has been used in human supplementation studies. MenaQ7® is a branded MK-7 preparation used in some clinical studies; no K2 form or branded ingredient is universally preferred, and ingredient-level findings do not establish superiority of a finished product.
• MK-4 (short-chain menaquinone): Shorter circulating persistence requires more frequent dosing. It was used in older Japanese clinical trials at pharmacological doses of 45 mg/day for osteoporosis treatment — well above typical supplement doses.

Featured Product: Wiley’s Finest® Omega-3 with K2 & D3

Wiley’s Finest® Omega-3 with K2 & D3 (60 Softgels)

One softgel: 500 mg EPA+DHA (375 mg EPA + 125 mg DHA) from Wild Alaska Pollock • 80 mcg MenaQ7® K2 (MK-7) • 2,000 IU Vitamin D3. MSC-certified. Non-GMO.

Pharmacist’s Note: As a PharmD, I discuss this combination product with patients looking to address multiple nutrient gaps in a single daily dose. Its ingredient profile is a formulation detail, not proof that the finished product produces the outcomes reported in studies of other doses or preparations. Patients on warfarin should consult their pharmacist before starting any K2-containing supplement.

What Does the Human Clinical Evidence Show?

Vitamin D — Bone and Fractures

• META-ANALYSIS Bischoff-Ferrari HA et al., JAMA 2004 (PMID: 15113819): Meta-analysis of RCTs; D3 supplementation reduced fall risk by 22% in older adults.
• SYSTEMATIC UMBRELLA REVIEW Chakhtoura M, Bacha DS, Gharios C, et al., JCEM 2022 (PMID: 34687206): Umbrella review of meta-analyses of controlled trials. The fracture findings did not support a consistent fracture-prevention benefit from vitamin D supplementation across generally healthy adults; results varied by population, baseline status, and intervention context.
• HUMAN RCT VITAL Fracture Analysis (PMID: 35939577) — 25,871 participants, D3 2,000 IU/day: Vitamin D3 did not significantly reduce total fractures, nonvertebral fractures, or hip fractures in generally healthy adults not selected for deficiency or osteoporosis.
• META-ANALYSIS 2024 de Souza MM et al. (PMID: 38997531) — 7 RCTs, 71,899 healthy older adults: No significant reduction in total fractures from vitamin D supplementation alone.

Grade: Vitamin D is essential for bone mineralization and correction of deficiency is clinically important. Vitamin D supplementation alone has NOT consistently reduced fractures in generally healthy, vitamin-D-replete adults. Benefit may depend on baseline deficiency, calcium status, population, and dosing.

Vitamin D — Respiratory Infections — MIXED / NOT CLEARLY ESTABLISHED

• META-ANALYSIS 2017 Martineau AR et al., BMJ 2017 (PMID: 28202713) — 25 RCTs, 11,321 participants: Reported a modest protective effect against acute respiratory infections overall; protective effect described as strongest in individuals with severe baseline deficiency.
• META-ANALYSIS 2025 Jolliffe DA et al., Lancet Diabetes Endocrinol 2025 (PMID: 39993397) — 40 studies, 61,589 participants: Vitamin D did not significantly reduce overall acute respiratory infection risk. Prespecified subgroup analyses did not find significant effect modification by baseline vitamin D status, age, dosing frequency, or dose size.

Grade: MIXED / NOT CLEARLY ESTABLISHED. The 2017 meta-analysis reported a modest benefit; the larger 2025 updated meta-analysis did not find a statistically significant overall effect.

Vitamin D — Cancer and Cardiovascular Outcomes — NOT ESTABLISHED (primary prevention)

• LARGE RCT (VITAL) Manson JE et al., NEJM 2019 (PMID: 30415629) — 25,871 participants, D3 2,000 IU/day: Did not significantly reduce primary cardiovascular or cancer endpoints in a generally vitamin-D-replete population.

Grade: NOT ESTABLISHED for primary prevention of cardiovascular events or cancer in vitamin-D-replete adults.

MK-7 — Postmenopausal Bone Health — MODERATE / SUPPORTIVE, WITH MIXED LONG-TERM RCT RESULTS

• HUMAN RCT Knapen MH et al., 2013 (PMID: 23525894) — 244 healthy postmenopausal women, MenaQ7® 180 mcg/day, 3 years: Significantly improved vitamin K status; attenuated age-related decline in BMD at lumbar spine and femoral neck; favorable effect on calculated bone-strength indices.
• HUMAN RCT Rønn SH et al., 2016 (PMID: 27625301) — 148 postmenopausal women with osteopenia, MK-7 375 mcg/day + calcium + vitamin D, 12 months: Substantially reduced undercarboxylated osteocalcin and preserved selected tibial trabecular microarchitecture versus placebo. This supports an adjunctive K2 effect in this population, not standalone D3+K2 superiority.
• HUMAN RCT Zhang Y et al., 2020 (PMID: 32060566) — 311 adults age 50–75, K2 50 or 90 mcg/day with or without calcium + D3, 1 year: In postmenopausal women, femoral-neck bone loss was significantly lower in 90-mcg K2 groups versus placebo; the effect was not demonstrated in men.
• HUMAN RCT — NULL BMD OUTCOME Rønn SH, Harsløf T, Oei L, Pedersen SB, Langdahl BL, Osteoporos Int 2021 (PMID: 33030563): Three-year randomized, placebo-controlled trial in postmenopausal women with osteopenia receiving MK-7 as an add-on to calcium and vitamin D. BMD declined in both groups, with no significant difference in BMD loss; bone-turnover and microarchitecture changes were also similar. This contrasts with some earlier favorable MK-7 studies.

K2 — Postmenopausal BMD Meta-Analyses — MODERATE / SUPPORTIVE

• META-ANALYSIS Ma ML et al., Front Public Health 2022 (PMID: 36033779) — 16 RCTs, 6,425 participants: Significant improvement in lumbar-spine BMD with K2 and reductions in undercarboxylated osteocalcin. Six-RCT fracture analysis showed no significant fracture reduction overall; benefit emerged in sensitivity analysis after excluding one heterogeneous study.

K2/postmenopausal BMD — MODERATE / SUPPORTIVE, but long-term RCT results are not uniformly positive. K2/fracture prevention — MIXED / NOT FIRMLY ESTABLISHED.

D3 + K2 Combination — Bone and BMD — LIMITED-TO-MODERATE / SUPPORTIVE

• META-ANALYSIS Kuang X et al., Food Funct 2020 (PMID: 32219282) — 8 RCTs, 971 participants: Vitamin D plus vitamin K was associated with improved total BMD and lower undercarboxylated osteocalcin; studies varied in population, formulation, and dosing.

Grade: LIMITED-TO-MODERATE / SUPPORTIVE. The combination shows a BMD and bone-marker signal in some analyses, but trial heterogeneity and the null long-term MK-7 RCT limit firm conclusions. The 80 mcg MK-7 + 2,000 IU D3 dose in Wiley’s has not been separately evaluated in these trials.

MK-7 — Arterial Stiffness and Vascular Calcification

• HUMAN RCT Knapen MH et al., Thromb Haemost 2015 (PMID: 25694037): In healthy postmenopausal women, MK-7 improved some measures of arterial stiffness, particularly among women with higher baseline stiffness.
• SYSTEMATIC REVIEW / META-ANALYSIS Li T, Wang Y, Tu WP, Front Nutr 2023 (PMID: 37252246): Systematic review and meta-analysis of 14 randomized controlled trials evaluating vitamin K supplementation and vascular-calcification-related outcomes. The review supports biological activity on vitamin-K-dependent pathways but does not establish that K2 prevents cardiovascular disease or reduces myocardial infarction, stroke, or mortality.
• HUMAN RCT Zwakenberg SR et al., AJCN 2019 (PMID: 31387121) — T2DM with established CVD, MK-7 360 mcg/day vs placebo, 6 months: MK-7 significantly reduced inactive dp-ucMGP, demonstrating biological activity on the MGP pathway, but did not significantly reduce vascular calcification on conventional CT.
• HUMAN RCT 2026 Vossen LM et al., JAMA Cardiol 2026 (PMID: 42268593) — 180 patients with symptomatic CAD and baseline CAC 50–400 AU, MK-7 360 mcg/day vs placebo, 2 years: CAC progressed less in the MK-7 group than the placebo group, with a statistically significant between-group difference. The clinical significance for plaque stability and cardiovascular outcomes remains uncertain.
• HUMAN RCT — NULL CALCIFICATION OUTCOME Haroon S, Davenport A, Ling LH, et al., Kidney Int Rep 2023 (PMID: 37705910): Trevasc-HDK randomized 178 hemodialysis patients to MK-7 360 mcg three times weekly or control for 18 months; 138 completed follow-up. The coronary-artery-calcification endpoint was not significantly different between groups. Hemodialysis patients are not equivalent to ordinary supplement users or symptomatic CAD patients.
• PROSPECTIVE COHORT Geleijnse JM et al., J Nutr 2004 (PMID: 15514282): Higher dietary K2 intake was associated with reduced coronary heart disease risk in the Rotterdam Study. This was observational dietary research, not a supplementation trial, so it does not establish causation.

MK-7 / arterial stiffness — LIMITED / SUPPORTIVE in a selected population. MGP carboxylation biomarkers — SUPPORTIVE HUMAN EVIDENCE. MK-7 / structural vascular calcification — LIMITED, MIXED, AND POPULATION-DEPENDENT: a 2026 RCT in symptomatic CAD reported attenuation of CAC progression, whereas trials in other high-risk populations, including hemodialysis patients, have not consistently demonstrated reduced calcification progression. Cardiovascular-event prevention remains unestablished. Universal requirement for K2 whenever taking D3 is not established.

Evidence Summary

Drug Interactions — Critical Information

• Warfarin (Vitamin K2): K2 can reduce warfarin’s anticoagulant effect. Patients on warfarin should not start K2 without physician supervision and INR monitoring. This applies to vitamin K-containing supplements.
• Novel anticoagulants such as apixaban and rivaroxaban: They do not act through vitamin K antagonism, but pharmacist review is still recommended before combining anticoagulants with supplements.
• Thiazide diuretics + Vitamin D3: May increase risk of hypercalcemia. Calcium monitoring may be appropriate.
• Granulomatous diseases such as sarcoidosis or tuberculosis: These conditions can increase endogenous D3 activation; supplementation may contribute to hypercalcemia. Consult a physician before use.
• Fish allergy: Wiley’s Finest contains Alaska Pollock and should not be used by people with fish allergy.

Dosing Guidance

• Vitamin D3: There is no single maintenance dose for every adult. 1,000–2,000 IU/day is a commonly used range for some adults, but dose should be individualized using 25(OH)D status, age, diet, medical conditions, and clinician guidance. Repletion of documented deficiency may require higher doses under pharmacist or physician supervision. The adult tolerable upper intake level is not a treatment target.
• Vitamin K2 (MK-7): Clinical trials have used substantially different doses, including 90, 180, 360, and 375 mcg/day. These study doses should not be presented as a universal recommendation, and the 80 mcg in Wiley’s Finest is not the same dose evaluated in most cited trials.
• Omega-3: The product supplies 500 mg EPA+DHA per softgel. Appropriate intake depends on dietary intake, medical history, medications, and the reason for use; there is no single supplement dose for every adult.

Who May Consider D3 + K2?

• Adults with documented vitamin D deficiency or a clinically recognized risk of deficiency
• Postmenopausal women with bone health concerns who want to discuss the mixed but potentially supportive K2 evidence with a healthcare professional
• Patients already taking D3 who wish to discuss whether K2 is appropriate for them with a pharmacist
• Adults with limited sun exposure or other recognized risk factors
• Patients with established cardiovascular disease or concerns about vascular calcification who wish to discuss the emerging, population-specific K2 evidence with their physician or pharmacist

Pharmacist’s Perspective

As a PharmD, I discuss vitamin D3 with patients routinely — particularly when there are risk factors for deficiency, bone health concerns, limited sun exposure, or a need to review the patient’s full medication list. The evidence for correcting vitamin D deficiency is well-established. The rationale for adding K2 alongside D3 is biologically sound and supported by mixed but promising human data, particularly for some postmenopausal bone outcomes and — based on one 2026 randomized trial — calcification progression in patients with symptomatic coronary artery disease. I discuss K2 as a possible consideration for appropriate patients — not a universal requirement — and always review anticoagulant medications first.

Free PharmD consultation available by phone or in-store: (408) 622-8068.

Frequently Asked Questions

Q: How do I know if I’m vitamin D deficient?
A: A blood test measuring 25(OH)D is the standard assessment. Results should be interpreted with your clinician because thresholds and treatment targets vary by guideline and clinical context.

Q: Can I take too much Vitamin D3?
A: Vitamin D toxicity can occur with excessive, sustained intake. Risk is generally lower at commonly used doses, but individual risk varies. Higher doses and prolonged use should be guided by a clinician, with blood-level monitoring when appropriate.

Q: I’m on warfarin. Can I take K2?
A: Only with physician supervision and INR monitoring. Do not start any vitamin K supplement while on warfarin without consulting your pharmacist and physician first.

Q: Should I take D3 with food?
A: Vitamin D is fat-soluble and is generally taken with a meal. Follow the product label and ask your pharmacist whether the formulation and your medical history call for any special instructions.

Related Clinical Insights Articles

• What Is Fucoidan? A Pharmacist’s Guide →
• AHCC: A Pharmacist’s Evidence Review →

Selected PubMed-Indexed Clinical Evidence

The following publications are the PubMed-indexed clinical and evidence-synthesis sources used in this article. The evidence applies to the populations, preparations, doses, and outcomes studied in each publication; it does not establish efficacy of any specific finished product unless that product was directly evaluated.

1. Bischoff-Ferrari HA, Dawson-Hughes B, Willett WC, Staehelin HB, Bazemore MG, Zee RY, Wong JB. Effect of Vitamin D on falls: a meta-analysis. JAMA. 2004;291(16):1999–2006. DOI: 10.1001/jama.291.16.1999. PMID: 15113819.
2. Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, van der Meer IM, Hofman A, Witteman JC. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100–3105. DOI: 10.1093/jn/134.11.3100. PMID: 15514282.
3. Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutr J. 2012;11:93. DOI: 10.1186/1475-2891-11-93. PMID: 23140417.
4. Knapen MH, Drummen NE, Smit E, Vermeer C, Theuwissen E. 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. PMID: 23525894.
5. Knapen MH, Braam LA, Drummen NE, Bekers O, Hoeks AP, Vermeer C. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. A double-blind randomised clinical trial. Thromb Haemost. 2015;113(5):1135–1144. DOI: 10.1160/TH14-08-0675. PMID: 25694037.
6. Manson JE, Cook NR, Lee IM, Christen W, Bassuk SS, Mora S, Gibson H, Gordon D, Copeland T, D’Agostino D, Friedenberg G, Ridge C, Bubes V, Giovannucci EL, Willett WC, Buring JE, VITAL Research Group. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. N Engl J Med. 2019;380(1):33–44. DOI: 10.1056/NEJMoa1809944. PMID: 30415629.
7. Zwakenberg SR, de Jong PA, Bartstra JW, et al. The effect of menaquinone-7 supplementation on vascular calcification in patients with diabetes: a randomized, double-blind, placebo-controlled trial. Am J Clin Nutr. 2019;110(4):883–890. DOI: 10.1093/ajcn/nqz147. PMID: 31387121.
8. Rønn SH, Pedersen SB, Langdahl BL, et al. Vitamin K2 (menaquinone-7) prevents age-related deterioration of trabecular bone microarchitecture at the tibia in postmenopausal women. Eur J Endocrinol. 2016;175(6):541–549. DOI: 10.1530/EJE-16-0498. PMID: 27625301.
9. 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. DOI: 10.1136/bmj.i6583. PMID: 28202713.
10. LeBoff MS, Chou SH, Ratliff KA, et al. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults. N Engl J Med. 2022;387(4):299–309. DOI: 10.1056/NEJMoa2202106. PMID: 35939577.
11. Kuang X, Liu C, Guo X, Li K, Deng Q, Li D. The combination effect of vitamin K and vitamin D on human bone quality: a meta-analysis of randomized controlled trials. Food Funct. 2020;11(4):3280–3297. DOI: 10.1039/c9fo03063h. PMID: 32219282.
12. Zhang Y, Liu Z, Duan L, Ji Y, Yang S, Zhang Y, Li H, Wang Y, Wang P, Chen J, Li Y. Effect of Low-Dose Vitamin K2 Supplementation on Bone Mineral Density in Middle-Aged and Elderly Chinese: A Randomized Controlled Study. Calcif Tissue Int. 2020;106(5):476–485. DOI: 10.1007/s00223-020-00669-4. PMID: 32060566.
13. Rønn SH, Harsløf T, Oei L, Pedersen SB, Langdahl BL. The effect of vitamin MK-7 on bone mineral density and microarchitecture in postmenopausal women with osteopenia, a 3-year randomized, placebo-controlled clinical trial. Osteoporos Int. 2021;32(1):185–191. DOI: 10.1007/s00198-020-05638-z. PMID: 33030563.
14. Ma ML, Ma ZJ, He YL, et al. Efficacy of vitamin K2 in the prevention and treatment of postmenopausal osteoporosis: A systematic review and meta-analysis of randomized controlled trials. Front Public Health. 2022;10:979649. DOI: 10.3389/fpubh.2022.979649. PMID: 36033779.
15. Chakhtoura M, Bacha DS, Gharios C, et al. Vitamin D Supplementation and Fractures in Adults: A Systematic Umbrella Review of Meta-Analyses of Controlled Trials. J Clin Endocrinol Metab. 2022;107(3):882–898. DOI: 10.1210/clinem/dgab742. PMID: 34687206.
16. de Souza MM, Moraes Dantas RL, Leão Durães V, Defante MLR, Mendes TB. Vitamin D Supplementation and the Incidence of Fractures in the Elderly Healthy Population: A Meta-analysis of Randomized Controlled Trials. J Gen Intern Med. 2024;39(14):2829–2836. DOI: 10.1007/s11606-024-08933-1. PMID: 38997531.
17. Jolliffe DA, Camargo CA Jr, Sluyter JD, et al. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Lancet Diabetes Endocrinol. 2025;13(4):307–320. DOI: 10.1016/S2213-8587(24)00348-6. PMID: 39993397.
18. Vossen LM, de Leeuw PW, Schurgers LJ, Heuts S, Adriaans BP, de Haan C, van Varik BJ, Kroon AA. Two Years of Menaquinone-7 Supplementation and Coronary Artery Calcification: A Randomized Clinical Trial. JAMA Cardiol. 2026;11(8):719–726. DOI: 10.1001/jamacardio.2026.1279. PMID: 42268593.
19. Li T, Wang Y, Tu WP. Vitamin K supplementation and vascular calcification: a systematic review and meta-analysis of randomized controlled trials. Front Nutr. 2023;10:1115069. DOI: 10.3389/fnut.2023.1115069. PMID: 37252246.
20. Haroon S, Davenport A, Ling LH, et al. Randomized Controlled Clinical Trial of the Effect of Treatment with Vitamin K2 on Vascular Calcification in Hemodialysis Patients (Trevasc-HDK). Kidney Int Rep. 2023;8(9):1741–1751. DOI: 10.1016/j.ekir.2023.06.011. PMID: 37705910.

Reviewed by:

Dai Tran, PharmD, MBA, B.S. • View full bio →

CEO & Lead Pharmacist, Khang Pharmacy • CA/MN/TX Licensed • 10+ Years Clinical Experience

Khang Pharmacy | 2451 S King Rd., Ste A1, San Jose, CA 95122 | (408) 622-8068 | www.khangpharmacy.com