Vitamin
Vitamin K1
Vitamin K1 requires 90 mcg daily for adult women and 120 mcg for men. It has 2 severe interactions, notably with Vitamin K2 (MK-7) and Warfarin.
What Vitamin K1 does
The plant form of vitamin K, essential for clotting factor synthesis.
Dietary sources include leafy greens. Interacts with warfarin.
How much you need
| Measure | Adult male | Adult female |
|---|---|---|
| Recommended intake | 120 mcg | 90 mcg |
| Upper intake level | None established | |
| Typical supplement dose | 100-300 mcg · 90-180 mcg | |
Interactions involving Vitamin K1
5 sourced rules| Pair | Severity | Mechanism | Action |
|---|---|---|---|
| Vitamin K2 (MK-7) × Warfarin | Severe | Warfarin blocks vitamin K epoxide reductase. Adding vitamin K restores clotting factor synthesis and directly antagonises the drug, which can drop the INR into a clot-risk range. | Do not start vitamin K1 or K2 without telling your prescriber. If you take it, the dose must stay consistent and the INR must be monitored.Source |
| Vitamin K1 × Warfarin | Severe | Vitamin K1 is the direct antidote pathway for warfarin. Large or erratic intakes destabilise anticoagulation. | Keep leafy-green intake steady rather than eliminating it, and never add a K supplement without INR monitoring.Source |
| Leafy greens × Warfarin | Moderate | Vitamin K1 from leafy greens competes with warfarin. The risk is variability more than the amount: a sudden jump in intake lowers the INR. | Keep your leafy-green intake consistent week to week rather than avoiding greens entirely.Source |
| Calcium citrate × Leafy greens | Mild | Spinach is high in oxalate, which binds calcium in the gut and makes that plant calcium largely unavailable. | Do not count spinach as a calcium source. Take supplemental calcium away from high-oxalate meals.Source |
| Vitamin D3 softgel × Vitamin K2 (MK-7) | Synergy | Vitamin D raises calcium absorption and vitamin K2 activates matrix Gla protein, which directs that calcium into bone rather than soft tissue. They are complementary, not redundant. | Take vitamin D3 and K2 together with a fat-containing meal. Typical pairing is 1000 IU D3 per 100 mcg K2.Source |