Understanding the Two Forms of Vitamin K
Vitamin K is not a single compound but rather a group of fat-soluble vitamins with two main dietary forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). These two forms differ in their sources, absorption, and roles within the body.
- Vitamin K1 (Phylloquinone): Primarily found in green leafy vegetables such as spinach, kale, and broccoli, as well as in some plant oils. The body's absorption of K1 is enhanced when consumed with dietary fat.
- Vitamin K2 (Menaquinones): Primarily found in animal products like meat, eggs, and dairy, as well as in fermented foods like natto. Different subtypes of K2 (MK-4 through MK-13) are found in varying concentrations depending on the food source. The gut microbiome can also produce some K2, though this is not sufficient to meet daily needs.
The Role of Fat Content in Milk's Vitamin K Levels
Because vitamin K is a fat-soluble vitamin, its presence in dairy products is directly correlated with the product's fat content. A study using mass spectrometry to analyze U.S. dairy products found a clear link.
- Full-Fat vs. Low-Fat Milk: The study found that total vitamin K concentrations were significantly higher in full-fat milk compared to 2% milk. Crucially, they detected menaquinones (vitamin K2) in full-fat milk, but not in fat-free yogurt, demonstrating the fat-dependence.
- Predominantly K2: The vitamin K detected in dairy was primarily menaquinones, especially MK-9, MK-10, and MK-11. This suggests that for those who consume full-fat dairy, milk provides a source of the K2 form.
Milk's Place Among Vitamin K Sources
While full-fat milk contains vitamin K2, it is not considered one of the richest dietary sources. The following comparison highlights how milk stacks up against other vitamin K sources, based on data from the NIH Office of Dietary Supplements and other sources.
| Food Source | Primary Vitamin K Type | Vitamin K Content (approx.) | Notes |
|---|---|---|---|
| Cooked Spinach (1/2 cup) | K1 | ~444 mcg | Excellent plant-based source |
| Natto (Japanese fermented soybeans, 3 oz) | K2 | ~781 mcg | Very rich fermented source |
| Hard Cheese (100g) | K2 | ~8-10 mcg | Content varies by type and fat |
| Whole Milk (1 cup) | K2 | ~0.5 mcg | Modest amount tied to fat content |
| Skim Milk (1 cup) | K2 (trace) | ~0 mcg | Negligible amount; removed with fat |
| Chicken (cooked, 3.5 oz) | K2 (MK-4) | ~36 mcg | Good animal source |
It's evident that a person would need to consume a very large quantity of whole milk to match the vitamin K intake from a small serving of leafy greens or fermented foods. Therefore, milk is best considered a supplementary source rather than a primary one.
Health Benefits Associated with Vitamin K
Adequate intake of both vitamin K1 and K2 is essential for several vital bodily functions, especially for blood coagulation and bone health.
Blood Coagulation
Vitamin K activates proteins necessary for blood clotting. This process is crucial for wound healing and preventing excessive bleeding. In fact, the name vitamin 'K' comes from the German word for coagulation, 'Koagulationsvitamin'. This function is particularly important in newborns, who are born with low vitamin K stores and require a prophylactic injection to prevent dangerous bleeding.
Bone Health
Beyond its role in blood clotting, vitamin K is a key nutrient for maintaining strong, healthy bones.
- Calcium Binding: It helps activate proteins like osteocalcin, which binds calcium to the bone matrix, ensuring proper bone mineralization.
- Osteoporosis Prevention: Studies have linked higher vitamin K intake with greater bone mineral density and a lower risk of fractures. This is especially true for vitamin K2, which is more effective at activating osteocalcin than K1.
Cardiovascular Health
Vitamin K also plays a role in cardiovascular health by regulating calcium. It activates Matrix Gla Protein (MGP), a protein that helps inhibit the calcification of arteries and heart valves. Higher intake of vitamin K2 has been associated with a reduced risk of coronary artery disease and a lower risk of cardiovascular events.
Conclusion
In summary, yes, vitamin K is found in milk, but its presence is largely dependent on the fat content. Full-fat milk provides modest amounts of vitamin K2, while low-fat and skim varieties contain very little. Milk should not be relied upon as a primary source of vitamin K, as other foods like leafy greens, fermented products, and certain cheeses offer significantly higher concentrations. For optimal health, a diverse diet that includes a range of vitamin K sources, both K1 and K2, is the best approach. For more information on dietary sources of vitamins, the NIH Office of Dietary Supplements is a reliable resource.
How to Find Your Vitamin K
To help guide your dietary choices, here is a list of foods that serve as good sources of vitamin K:
- Green Leafy Vegetables: High in vitamin K1, these include kale, spinach, collard greens, turnip greens, and broccoli.
- Vegetable Oils: Oils such as soybean and canola are also good sources of vitamin K1.
- Fermented Foods: Natto is a remarkably rich source of vitamin K2, particularly the MK-7 subtype.
- Cheeses: Especially soft and fermented cheeses, contain varying levels of vitamin K2.
- Animal Products: Meat, eggs, and full-fat dairy products contribute to your vitamin K2 intake.
By incorporating a mix of these foods into your diet, you can ensure a steady intake of both forms of this essential nutrient.
Conclusion
Is vitamin K found in milk? The answer is yes, but with a major caveat: it is primarily found in the fat portion of dairy. This means that whole milk contains more K2 than low-fat or skim versions. However, milk is not the most potent source of this nutrient. Foods like leafy green vegetables (for K1) and fermented products or cheese (for K2) provide much higher concentrations. While milk can contribute to overall vitamin K intake, relying on a balanced diet rich in varied sources is the most effective way to meet your body's needs for blood clotting, bone health, and cardiovascular support.
Disclaimer
This article provides general information and should not be taken as medical advice. Always consult with a healthcare professional before making significant changes to your diet or supplementing with vitamins, especially if you are on medications that interact with vitamin K, such as blood thinners.
References
For further reading and verification of the information provided in this article, please refer to the following sources:
- Fu, X., Harshman, S., Shen, X., Haytowitz, D., & Karl, J. (2017). Multiple Vitamin K Forms Exist in Dairy Foods. Current Developments in Nutrition.
- U.S. Dairy. (2025). Do Dairy Foods Contain Vitamin K?.
- NIH Office of Dietary Supplements. (2021). Vitamin K - Consumer Fact Sheet.
- National Institutes of Health (NIH). (2025). Drugs and Lactation Database (LactMed®): Vitamin K.
- Medical News Today. (2018). Foods high in vitamin K: 40 of the best.
