Vitamin K: Two Forms With Different Roles
Vitamin K is a fat-soluble vitamin best known for its role in blood clotting, but it also plays an essential role in bone metabolism and cardiovascular health. There are two main dietary forms:
🥬 Vitamin K1 (Phylloquinone)
Primary dietary form
Found abundantly in leafy green vegetables. Primarily supports blood coagulation. Rapidly cleared from the body — must be consumed regularly.
🫘 Vitamin K2 (Menaquinone)
Bone & cardiovascular form
Found in fermented foods and animal products. Activates proteins (osteocalcin, MGP) that direct calcium into bones and away from arteries. MK-7 has a half-life of ~72 hours.
The FDA Daily Value for vitamin K is 120µg per day. Most guidelines focus on K1, but emerging research highlights K2 (especially MK-7) as the form with distinct bone and vascular benefits not provided by K1 alone.
Top Vitamin K1 Sources (Per 100g, USDA Data)
| Food | K1 (µg/100g) |
|---|---|
| Kale (cooked) | 817 |
| Spinach (cooked) | 540 |
| Collard greens (cooked) | 623 |
| Swiss chard (cooked) | 327 |
| Broccoli (cooked) | 141 |
| Brussels sprouts (cooked) | 194 |
| Parsley (raw) | 1,640 |
| Green onions (raw) | 207 |
| Edamame (cooked) | 31 |
| Lettuce, romaine (raw) | 103 |
Source: USDA FoodData Central — SR Legacy & Foundation Foods.
Top Vitamin K2 Sources
| Food | K2 (µg/100g) |
|---|---|
| Natto (fermented soybeans) | 939 |
| Gouda / Brie cheese | 76 |
| Chicken liver (cooked) | 12.6 |
| Egg yolk | 9.5 |
| Hard cheese (e.g. Edam) | 50 |
| Butter | 15 |
| Chicken breast (cooked) | 5.1 |
K2 data varies by analytical method. MK-7 from natto has the longest half-life and strongest evidence for bone and arterial health.
Why K2 MK-7 Is Difficult to Get From Diet Alone
The Natto Problem
Natto is by far the richest dietary K2 source, but it has a strong flavor and fermented aroma that many people outside Japan find unpalatable. A typical 50g serving of natto provides ~470µg MK-7 — far more than needed. But if you don't eat natto, reaching therapeutic K2 levels from diet alone is very difficult.
Fermented cheeses contain modest K2, but you would need to eat large amounts daily to approach the 90–200µg/day doses studied in clinical trials for bone density.
The K2 + Vitamin D3 Synergy
☀️ Vitamin D3 increases calcium absorption
D3 upregulates intestinal calcium transport, increasing the amount of calcium entering your bloodstream from food.
🫀 K2 MK-7 directs calcium to the right places
K2 activates osteocalcin (routes calcium into bone mineral matrix) and Matrix Gla Protein (blocks calcium from depositing in arterial walls).
⚖️ Without K2, high-dose D3 may increase vascular calcium
Some researchers caution that supplementing D3 without adequate K2 could push calcium into arteries. Taking both together addresses this concern.
Key Takeaways
- ✓Vitamin K exists in two main dietary forms: K1 (leafy greens, blood clotting) and K2 (fermented foods, bone & arteries)
- ✓Leafy greens like kale, spinach, and broccoli are excellent daily K1 sources and easy to include in any diet
- ✓Natto is the only food with very high K2 MK-7; if you don't eat natto, supplementing K2 MK-7 is practical
- ✓K2 and vitamin D3 work synergistically — K2 directs the calcium that D3 absorbs into bones rather than arteries
- ✓People on warfarin (blood thinner) should consult their doctor before significantly increasing vitamin K intake
Data Source
USDA FoodData Central — Foundation Foods & SR Legacy (Public Domain)