Match your vitamin D dose to the right K2 (MK-4 or MK-7) amount based on bone-health trial ratios. Calculator also flags the magnesium cofactor that most stack labels ignore. Math + RCT references, not medical advice.
Your stack
D : K2 ratios used in trials
| Population | Vit D dose | K2 form | K2 dose | Ratio (IU D : mcg K2) |
|---|---|---|---|---|
| Postmenopausal bone density (Knapen 2013) | — (no D control) | MK-7 | 180 mcg | N/A (K2-only) |
| Bone density (Ushiroyama 2002) | 800 IU | MK-4 | 45 mg | — (pharmacologic MK-4) |
| Common 1:50 stack supplement | 2,000 IU | MK-7 | 100 mcg | 20 IU : 1 mcg |
| “Premium” stack (Thorne, Pure Encapsulations) | 5,000 IU | MK-7 | 90-180 mcg | 28-55 IU : 1 mcg |
| Mercola high-dose | 10,000 IU | MK-7 | 180 mcg | 55 IU : 1 mcg |
A common rule-of-thumb is 100 mcg MK-7 per 5,000 IU vitamin D, but RCT evidence directly comparing D-only vs D+K2 stacks is limited. Bone-health benefits of K2 are most clearly demonstrated in dedicated K2 trials.
The magnesium cofactor most stack labels forget
Vitamin D metabolism uses magnesium-dependent enzymes at multiple steps (CYP2R1 hydroxylase, CYP27B1 activation, vitamin D-binding protein). Magnesium deficiency can reduce the body’s ability to convert D3 to its active form (1,25-OH D). RDA for magnesium is 310-420 mg/day depending on age and sex.
- If you supplement D > 2,000 IU, ensure you meet the magnesium RDA from food + supplement combined.
- Best magnesium forms for the stack: glycinate (gentle, well-absorbed), citrate (mild laxative effect), malate (energy). See our magnesium dose calculator for elemental Mg by form.
- Avoid: magnesium oxide (mostly laxative, poorly absorbed for systemic effects).
When NOT to stack D with K2
- On warfarin (Coumadin): K2 affects clotting factor synthesis and can interfere with INR control. Consult prescriber before any K2 supplement.
- On certain antibiotics: long-term broad-spectrum antibiotics affect gut bacteria that produce K2; supplementation may be appropriate but should be coordinated with prescriber.
- For kidney disease: vitamin D metabolism is impaired in CKD; use only with renal/endocrine specialist guidance.
- For hyperparathyroidism or sarcoidosis: calcium dysregulation contraindicates high-dose vitamin D without specialist supervision.
D3 vs D2 in stacks
Stack products use D3 (cholecalciferol) almost exclusively. D2 (ergocalciferol) is the prescription form for short-term high-dose correction (50,000 IU weekly). For daily K2 stacks, D3 is the standard choice — it raises serum 25(OH)D more efficiently than D2 in most studies.