Understanding the Forms of Vitamin K
Vitamin K is a crucial fat-soluble nutrient, but it's not a single compound. Instead, it is a family of compounds primarily divided into two groups: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). Vitamin K1 is most commonly found in plant-based foods, especially green leafy vegetables. Vitamin K2, on the other hand, is primarily found in animal products and fermented foods. Though both forms are important for health, their metabolic functions can differ slightly. The answer to which food has the most vitamin K often depends on which form you are prioritizing.
The Vitamin K Powerhouse: Natto
When measured by weight or standard serving size, one food stands out as a clear winner for overall vitamin K content, especially vitamin K2: natto. This traditional Japanese dish is made from fermented soybeans and is an exceptionally concentrated source of menaquinone-7 (MK-7), a form of vitamin K2. A single 3-ounce serving can provide over 700% of the Daily Value, making it the richest food source by a significant margin. Its content is so high because the fermentation process by bacteria like Bacillus subtilis is a natural producer of menaquinones.
Top Tier Vitamin K1 from Leafy Greens
While natto dominates the K2 category, a variety of dark green leafy vegetables are the definitive champions for vitamin K1. Cooking methods can sometimes change the nutrient profile, but in general, these vegetables provide hundreds of micrograms per 100-gram serving. Some of the most potent options include:
- Raw Swiss Chard: With approximately 830 micrograms per 100g, raw Swiss chard is a top contender.
- Raw Dandelion Greens: Offering about 778 micrograms per 100g, these greens are packed with nutrients.
- Cooked Collard Greens: A half-cup serving of cooked collard greens contains a high amount of vitamin K.
- Cooked Mustard Greens: Similarly, cooked mustard greens provide a very high concentration of vitamin K.
- Raw Spinach: A single cup of raw spinach contains more than the daily requirement for an adult.
- Cooked Kale: A cup of cooked kale is also exceptionally high in vitamin K.
Comparing the Best Food Sources of Vitamin K
This table compares some of the highest-ranking food sources of vitamin K based on typical serving sizes and concentrations.
| Food Source | Form of Vitamin K | Concentration (per 100g) | Notes |
|---|---|---|---|
| Natto | K2 (MK-7) | ~939-998 mcg | Extremely high concentration, particularly in MK-7. |
| Fresh Parsley | K1 | ~1640 mcg | Exceptionally high per 100g, but realistic serving sizes are small. |
| Raw Swiss Chard | K1 | ~830 mcg | Very high concentration, often consumed in larger portions than herbs. |
| Raw Dandelion Greens | K1 | ~778 mcg | Potent source of K1. |
| Cooked Collard Greens | K1 | ~623 mcg | High concentration after cooking. |
| Cooked Mustard Greens | K1 | ~593 mcg | High concentration of K1. |
| Cooked Spinach | K1 | ~541 mcg | Very rich source of K1. |
| Soybean Oil | K1 | ~184 mcg | A non-vegetable source of K1. |
Maximizing Absorption
Since vitamin K is a fat-soluble vitamin, combining it with a small amount of dietary fat can significantly increase its absorption. For example, drizzling olive oil on a spinach salad or sautéing kale with a little butter or oil will help your body absorb more of the vitamin K. This is particularly important for plant-based sources of vitamin K1.
The Role of Vitamin K in Your Body
Beyond being a dietary benchmark, vitamin K plays a critical role in several bodily functions:
- Blood Clotting: This is the best-known function of vitamin K. The vitamin is essential for synthesizing proteins that are necessary for blood coagulation. A deficiency can lead to uncontrolled bleeding and easy bruising. This is why people on blood-thinning medications like warfarin must monitor their vitamin K intake carefully.
- Bone Health: Vitamin K is a necessary component for the creation of bone-building proteins, such as osteocalcin. It helps to bind calcium to the bone matrix, contributing to bone mineralization and strength. Studies have linked higher vitamin K intake to improved bone mineral density and a lower risk of fractures.
- Cardiovascular Health: Recent studies suggest that vitamin K may play a role in preventing arterial calcification, which is a major contributor to heart disease. This is primarily associated with vitamin K2, which helps activate proteins that inhibit calcium buildup in the arteries.
Other Rich Sources of Vitamin K
In addition to the top contenders, several other foods can contribute significantly to your vitamin K intake:
- Cruciferous Vegetables: Broccoli, Brussels sprouts, and cabbage contain respectable amounts of vitamin K.
- Fermented Dairy and Meat: Some cheeses (like hard and soft varieties) and animal livers contain vitamin K2.
- Certain Fruits: While lower in concentration than greens, fruits like blueberries, blackberries, and kiwis offer moderate amounts.
- Herbs: As noted in the table, many dried and fresh herbs, like basil, sage, and parsley, are incredibly high in vitamin K per weight, making them excellent additions to dishes for a small boost.
Conclusion
When asking what food source has the most vitamin K, the answer is complex but clear. Natto is the overall winner for sheer concentration, particularly of the K2 variety. However, for vitamin K1, an abundance of readily available dark leafy greens like Swiss chard, dandelion greens, and spinach provide massive amounts. Incorporating a variety of these foods into your diet, especially paired with a source of healthy fat, is the best strategy to ensure adequate intake for both blood clotting and bone health.
NIH Office of Dietary Supplements: Vitamin K Fact Sheet for Consumers
