Understanding the Two Forms of Vitamin K
Before diving into the list of foods, it's essential to understand that vitamin K comes in two primary forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). They function differently in the body and are found in different food types.
- Vitamin K1 (Phylloquinone): Primarily found in plant-based foods, especially dark, leafy green vegetables. It plays a crucial role in blood clotting.
- Vitamin K2 (Menaquinone): Found in fermented foods and animal products. It is important for bone health and preventing arterial calcification.
Top Tier: The Absolute Highest Sources
When considering which food is very high in vitamin K, a few stand out significantly due to their exceptional concentration.
Natto
This traditional Japanese food made from fermented soybeans is the single richest dietary source of vitamin K2. Just one ounce (around 28g) can provide hundreds of micrograms, far exceeding the daily recommended intake. Its unique fermentation process is responsible for the high menaquinone content, making it an excellent choice for supporting bone and heart health.
Dried Herbs
On a gram-for-gram basis, certain dried herbs are astonishingly high in vitamin K1. While you consume them in much smaller quantities than vegetables, they are worth noting.
- Dried Basil: Extremely concentrated, with 100g containing over 1700 mcg.
- Dried Sage and Thyme: Also provide exceptionally high levels of vitamin K per 100g.
- Fresh Parsley: A single sprig of fresh parsley can deliver a significant amount of vitamin K.
Leafy Greens: The Most Common High-Vitamin K Foods
Dark, leafy green vegetables are the most accessible and common sources of vitamin K1. Cooking these vegetables can sometimes increase their vitamin K content by concentrating the nutrients as water evaporates.
- Cooked Kale: A cup of cooked kale can offer several hundred micrograms of vitamin K.
- Cooked Collard Greens: Another top contender, a half-cup serving provides a large portion of the daily value.
- Cooked Turnip Greens: This vegetable offers a very high concentration of vitamin K when cooked.
- Cooked Spinach: A cup of cooked spinach is a potent source of vitamin K, delivering many times the daily recommended value. Raw spinach also offers a high amount per cup.
Other Notable Vegetable and Fruit Sources
While not as concentrated as the top leafy greens, many other vegetables and fruits contribute valuable amounts of vitamin K to your diet.
- Broccoli and Brussels Sprouts: These cruciferous vegetables are both excellent sources, especially when cooked.
- Asparagus: Another vegetable with a solid vitamin K profile.
- Avocado: This fruit is a surprisingly good source, with one medium fruit providing a decent boost to your intake. Since vitamin K is fat-soluble, the healthy fats in avocado may aid its absorption.
- Blueberries and Blackberries: These berries contain moderate levels of vitamin K.
- Kiwi: One kiwi fruit provides a helpful amount of vitamin K.
Vitamin K from Animal and Fermented Foods
For those seeking vitamin K2, animal and fermented products are key. The K2 content can vary based on the animal's diet (e.g., grass-fed vs. grain-fed) and the fermentation process.
- Organ Meats: Beef liver, for example, is a very nutritious food and contains good amounts of vitamin K2.
- Cheese: Certain types of cheese, especially aged varieties like Gouda and soft cheeses like Munster, are known to contain K2.
- Eggs: The yolks of eggs, particularly from pasture-raised chickens, contain some vitamin K2.
- Chicken and Pork: Dark meat chicken and some pork products, like bacon, contain vitamin K2.
How Preparation Affects Vitamin K Content
How you prepare your food can affect its vitamin K concentration. As mentioned, cooking certain leafy greens can increase the amount of vitamin K per serving by reducing the water content. The presence of fat can also improve absorption, as vitamin K is fat-soluble. For example, drizzling some soybean or canola oil (which also contains vitamin K) on your spinach can boost absorption.
A Comparison of High Vitamin K Foods
| Food (per 100g) | Primary Vitamin K Type | Approximate Vitamin K (mcg) | Notes |
|---|---|---|---|
| Natto (Fermented Soybeans) | K2 | ~998 | Highest K2 source; unique flavor. |
| Swiss Chard (Raw) | K1 | ~830 | Extremely high concentration. |
| Mustard Greens (Cooked) | K1 | ~593 | Very dense source when cooked. |
| Cooked Spinach | K1 | ~541 | Potent source, easily added to many meals. |
| Beef Liver | K2 | ~106 | Good animal-based K2 source. |
| Broccoli (Cooked) | K1 | ~141 | Accessible and versatile vegetable. |
| Soft Cheese (e.g., Munster) | K2 | ~506 | High K2 content in a dairy source. |
| Avocado (Medium) | K1 | ~21 | Decent amount, and fats aid absorption. |
Important Note for Those on Blood Thinners
Individuals taking blood-thinning medications like warfarin (Coumadin) should consult their healthcare provider before making significant dietary changes regarding vitamin K. Consistent vitamin K intake is critical for these individuals because sudden fluctuations can interfere with the medication's effectiveness. For most people not on this medication, consuming a variety of vitamin K-rich foods is a healthy strategy.
Conclusion
While a single food is not universally the highest source for everyone due to variations in K1 and K2 content, fermented soybeans (natto) provide the most vitamin K2, and cooked leafy greens like mustard greens and spinach offer the highest concentrations of vitamin K1. By incorporating a mix of these powerhouses—from natto for the K2 benefits to the readily available K1-rich leafy greens and herbs—you can ensure your body receives an ample supply of this essential nutrient for healthy blood clotting, bone density, and heart function. Making informed food choices, particularly when adding fats to aid absorption, can maximize the health benefits derived from these vitamin K champions.
Visit the NIH Office of Dietary Supplements for more details on Vitamin K.
