Vitamin D3 and K2 (MK-7) from trials and guidelines: who benefits, what large trials found, safety limits, and monthly cost at the dose used in a trial.
Researched from published studies and manufacturer specifications, checked .
We have not tested products ourselves. How we research
The 2024 Endocrine Society guideline suggests against vitamin D above the standard intake for healthy adults under 75, and suggests it for children, people over 75, pregnancy and high-risk prediabetes. K2 evidence is thin. Vitamin K interacts with warfarin. Ask a doctor before starting either.
Talk to your doctor first. This is general information, not medical advice. Supplements and devices can interact with medicines and health conditions. We quote study protocols for context and do not recommend doses.
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The short answer: for healthy adults under 75, the 2024 Endocrine Society guideline suggests against taking vitamin D above the standard recommended intake to prevent disease; it suggests supplementing for children, people over 75, pregnancy and high-risk prediabetes. The largest trial, VITAL, found no reduction in cancer or major cardiovascular events. Evidence for vitamin K2 is smaller still, and vitamin K interacts with warfarin. Talk to your doctor before starting either, and before taking more than the standard amounts.
Grades follow the rubric.
| Question | Grade | Evidence | Limit |
|---|---|---|---|
| Vitamin D corrects deficiency and prevents rickets | Strong (established indication) | The Endocrine Society guideline suggests empiric vitamin D for ages 1 to 18 to prevent nutritional rickets. | A guideline for people without established indications; it does not replace standard intake recommendations. |
| Vitamin D prevents cancer or heart disease in adults | Weak | VITAL, 25,871 adults on 2,000 IU/day for 5.3 years: cancer HR 0.96, major cardiovascular events HR 0.97, neither significant. | Most participants were not deficient, so it says little about deficient people. |
| Vitamin D lowers mortality | Weak, mixed | A meta-analysis of 52 RCTs (75,454 people): no effect on all-cause mortality (RR 0.98), but cancer death fell 16%. The Endocrine Society notes a potential mortality benefit at 75 and older. | Cancer-death finding is secondary; guideline suggestion is for over-75s only. |
| Vitamin K2 (MK-7) and arterial stiffness | Emerging | One 3-year RCT of 244 postmenopausal women found lower arterial stiffness measures. | A single trial; an author works with the MK-7 supplier VitaK. |
| Vitamin K2 and bone | Emerging | A meta-analysis of 16 RCTs (6,425 women) found better lumbar spine density; the overall fracture effect was not significant (RR 0.96) until one heterogeneous study was excluded. | Postmenopausal women with osteoporosis; results depend on excluding a study. |
| D3 plus K2 together beats D3 alone | Not shown | We did not find a trial comparing them for hard outcomes. | The case for combining rests on mechanism, not proof. |
The Endocrine Society found no clinical-trial evidence to support routine 25(OH)D screening in the general population and suggests against routine testing without an established indication; it also found no clear optimal blood level for disease prevention. It notes trial doses varied a great deal and that optimal doses remain unclear. The NHS advises adults need 10 micrograms (400 IU) a day and to avoid more than 100 micrograms (4,000 IU) a day. This page does not give a personal dose; that is a question for your doctor, informed by a test if you have a reason to have one.
From our cost per study dose dataset: brand pages read 28 Sept 2026 (Nutricost, Momentous and Jarrow prices re-checked 29 Sept 2026, unchanged), USD, before tax and shipping, at the dose used in the cited trial (not a suggested dose).
| Product | Price | Trial dose used | Per month | Third-party testing stated |
|---|---|---|---|---|
| Nutricost Vegan Vitamin D3 5,000 IU (60) | $11.97 | 2,000 IU/day (VITAL) | $2.39 | generic “third-party tested” banner, no certifier (NSF certified facility) |
| Thorne Vitamin D-5,000 (60) | $20 | 2,000 IU/day (VITAL) | $4.00 | NSF Certified for Sport (stated on page) |
| Momentous Vitamin D3 2000 IU (60) | $19.99 | 2,000 IU/day (VITAL) | $9.99 | NSF Certified for Sport (stated on page) |
| Nutricost Vitamin K2 MK-7 (120) | $15.97 | MK-7 180 mcg/day (Knapen 2015) | $7.19 | generic “third-party tested” banner, no certifier |
| Jarrow MK-7 180 mcg (30) | $21.99 | MK-7 180 mcg/day (Knapen 2015) | $21.99 | none stated |
Vitamin D is cheap at the dose VITAL used; K2 is more expensive per month. You can compare more compounds in the full table. To see where D3 and K2 sit against other supplements, read the graded longevity supplement ladder. Testing is covered in the biomarker guide, and other bone and vascular nutrients in magnesium and omega-3. The complete stack shows how the compounds are sequenced.
For what a certifier such as NSF checks, see third-party tested supplements compared.
Researched from PubMed abstract records for the guideline, trials and reviews (29 Sept 2026), the NHS vitamin pages, and brand pages for prices (28 Sept 2026). Grades are our judgement using the published rubric. The NIH Office of Dietary Supplements pages could not be read by our tools, so we used the NHS for intake and limits; check your own country’s guidance. We did not test any product. General information, not medical advice: talk to your doctor before starting vitamin D or K, especially with kidney disease, high calcium, or anticoagulant treatment.
We found no trial in our search that tests D3 plus K2 against D3 alone for bone or heart outcomes, so the case for combining them rests on mechanism, not proof. K2 has its own small evidence base, and vitamin K interacts with warfarin, so ask a doctor before using it.
The 2024 Endocrine Society guideline suggests against taking vitamin D above the recommended intake to lower disease risk in healthy adults under 75, and suggests supplementation for children, people over 75, pregnancy and high-risk prediabetes. The NHS advises everyone to consider a supplement in autumn and winter and some groups year-round. A doctor can say which applies to you.
The NHS says not to take more than 100 micrograms (4,000 IU) a day because it could be harmful; too much over a long period can cause too much calcium in the body (hypercalcaemia), which can weaken bones and damage the kidneys and heart. Check limits for your country and talk to your doctor.
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