Natto: The #1 Champion of Vitamin K
When answering the question, "What food has the highest source of vitamin K?" the answer is unequivocally natto. This traditional Japanese dish is made from fermented soybeans and is an incredibly potent source of vitamin K, specifically the menaquinone form, or vitamin K2. A single 3-ounce serving can provide over 700% of the daily recommended value, making it a superfood for anyone looking to boost their vitamin K intake naturally. For those unfamiliar with its strong flavor and sticky texture, integrating it into your diet may take some getting used to. However, its nutritional benefits, which include significant amounts of both K1 and K2, are unmatched by other common food sources.
Leafy Greens: Powerhouses of Vitamin K1
Outside of natto, the most abundant sources of vitamin K are dark, leafy green vegetables. These plants are rich in vitamin K1, or phylloquinone.
Some of the top leafy green sources include:
- Kale (cooked): Just one cup of cooked kale can provide well over the daily recommended amount of vitamin K.
- Collard Greens (cooked): Boiled collard greens are another powerhouse, with a half-cup serving offering hundreds of micrograms.
- Spinach: Whether raw in a salad or cooked, spinach is an excellent source of K1.
- Turnip Greens: These greens are also packed with vitamin K and other essential nutrients.
- Swiss Chard: A single raw leaf can deliver a substantial portion of your daily needs.
For optimal absorption of these fat-soluble vitamins, it is best to consume leafy greens with a healthy fat source, like olive oil in a salad dressing.
K1 vs. K2: Understanding the Difference
Vitamin K is a group of fat-soluble compounds, with the two most common forms being K1 (phylloquinone) and K2 (menaquinone).
- Vitamin K1: Primarily found in plant-based foods, especially leafy greens. Its main function is related to blood clotting, ensuring wounds can heal properly. The body absorbs K1 less efficiently than K2.
- Vitamin K2: Found in fermented foods like natto and some animal products, such as meat and cheese. K2 is primarily known for its role in bone metabolism and heart health by helping to prevent arterial calcification. Some K2 is also produced by bacteria in the human gut.
Beyond Greens: Other Vitamin K Sources
While leafy greens and natto lead the way, other foods can contribute significantly to your vitamin K intake.
Vegetables
- Brussels Sprouts: A cup of cooked Brussels sprouts provides a very high amount of vitamin K.
- Broccoli: Cooked broccoli offers a good dose of the vitamin.
- Cabbage: A more common vegetable that contributes to daily needs.
Animal and Fermented Products
- Hard Cheeses: Certain hard and blue cheeses contain notable amounts of vitamin K2.
- Organ Meats: Liver, particularly from goose or beef, contains vitamin K2.
- Egg Yolks: A modest source of K2.
- Chicken: Meat from chicken, especially thighs and liver, contains K2.
Fruits and Other Sources
- Blueberries and Blackberries: These berries offer moderate amounts of vitamin K.
- Pomegranate: Both the fruit and juice contain some vitamin K.
- Soybean Oil: A good source of vitamin K1, although whole soybeans offer more overall nutrition.
Key Functions of Vitamin K
Vitamin K's roles go beyond just blood clotting. It is essential for producing proteins required for multiple physiological processes.
- Blood Coagulation: Vitamin K is a cofactor for the production of proteins in the liver that are crucial for blood clotting, including prothrombin. Without sufficient vitamin K, the clotting process is severely impaired.
- Bone Health: The vitamin is involved in synthesizing osteocalcin, a protein needed for healthy bone tissue and binding calcium. This supports bone mineralization and density, potentially lowering fracture risk.
- Cardiovascular Health: Vitamin K is involved in the production of Matrix Gla Protein (MGP), which helps prevent the calcification or hardening of heart arteries. This helps maintain heart health and arterial flexibility.
High Vitamin K Food Comparison
| Food (Cooked) | Serving Size | Vitamin K (mcg) | Percent Daily Value* | Primary Form |
|---|---|---|---|---|
| Natto | 3 oz | 850 | 708% | K2 |
| Collard Greens | ½ cup | 305 | 254% | K1 |
| Kale | ½ cup | 247 | 205% | K1 |
| Spinach (Raw) | 1 cup | 145 | 121% | K1 |
| Brussels Sprouts | ½ cup | 109 | 91% | K1 |
| Broccoli | ½ cup | 110 | 92% | K1 |
*Based on a 120 mcg daily value.
Conclusion: How to Get Enough Vitamin K
While natto is the ultimate winner for the highest concentration of vitamin K, incorporating a variety of sources is the best strategy for a balanced intake. Including an assortment of dark leafy greens, cruciferous vegetables, and other foods ensures you get both K1 and K2. For most people, a well-rounded diet with these ingredients provides enough vitamin K to prevent a deficiency. Since vitamin K is fat-soluble, pairing these foods with a source of dietary fat, like olive oil, avocado, or nuts, will maximize absorption. If you have a condition affecting absorption or are on blood-thinning medication like warfarin, consult your doctor before significantly changing your vitamin K intake, as it can affect medication efficacy.
By focusing on these nutrient-dense foods, you can support your body's vital functions, from proper blood clotting to maintaining strong bones and a healthy heart. For additional dietary information, a reliable resource is the NIH Office of Dietary Supplements' fact sheet on vitamin K.
