Vitamin K is a fat-soluble vitamin essential for several critical bodily functions, including blood clotting and bone metabolism. However, what many people don't realize is that vitamin K comes in two primary forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinone).
Vitamin K1 vs. Vitamin K2: The Key Difference
- Vitamin K1: This form is found predominantly in plants, especially leafy green vegetables like spinach, kale, and broccoli. It is most well-known for its role in the blood coagulation process.
- Vitamin K2: This form is primarily found in animal-based and fermented foods, including meat, eggs, and dairy products. Vitamin K2 is particularly noted for its potential role in promoting bone health and preventing arterial calcification, which supports cardiovascular health.
How Milk Delivers Vitamin K
The short answer is yes, milk does have vitamin K in it, but the type and amount depend heavily on the milk's fat content. The vitamin K found in cow's milk is predominantly the K2 form, which is synthesized by bacteria in the ruminant digestive system. Because vitamin K is fat-soluble, it is retained in the fat portion of the milk, not the watery portion. This is why the amount of vitamin K in milk is directly proportional to its fat content.
- Full-Fat (Whole) Milk: Contains the highest levels of vitamin K2, making it a valuable dietary source for this micronutrient.
- Reduced-Fat and Low-Fat Milk: As the fat is removed, the vitamin K content is significantly reduced. Studies have shown that reduced-fat and fat-free dairy products contain only a fraction (sometimes as low as 5-22%) of the vitamin K found in their full-fat counterparts.
- Skim (Nonfat) Milk: Contains very little to no vitamin K because nearly all the fat has been removed during processing.
Comparison of Vitamin K Content in Different Milk Types
| Milk Type (per 100g) | Total Vitamin K Content (µg) | Key Vitamin K Form(s) | Vitamin K Source | Notes |
|---|---|---|---|---|
| Full-Fat Milk (4%) | 38.1 | Primarily MK9, MK10, MK11 | Fat content from the cow | Significant source of K2. |
| Reduced-Fat Milk (2%) | 19.4 | MK9, MK10, MK11 | Reduced fat content | Vitamin K content is halved. |
| Low-Fat Milk (1%) | 12.9 | MK9, MK10, MK11 | Reduced fat content | Vitamin K content is significantly lower. |
| Nonfat (Skim) Milk | 7.7 | Minimal | Very low fat content | Little to no vitamin K present. |
It's important to note that these figures are averages and can vary based on factors like the cow's diet and seasonality.
Broader Dairy Sources of Vitamin K2
Milk isn't the only source of vitamin K in dairy products. Fermentation processes introduce or enhance specific forms of menaquinone, making certain cheeses exceptionally high in vitamin K2.
- Cheeses: Varieties like soft cheeses, blue cheese, and hard cheese can contain very high levels of vitamin K2 due to bacterial fermentation during aging. For example, soft cheese was found to contain 506 µg/100 g, and hard cheese 282 µg/100 g in one study.
- Yogurt and Kefir: These fermented dairy products can also contain vitamin K2, though their content may be lower than aged cheeses due to shorter fermentation times. As with milk, full-fat versions are better sources.
- Butter: As a highly concentrated dairy fat, butter contains substantial amounts of vitamin K2.
The Importance of Vitamin K in Your Diet
Both Vitamin K1 and K2 are vital for health. While K1 is crucial for proper blood clotting, K2 offers unique benefits for bone and cardiovascular health. For bone health, vitamin K helps activate proteins like osteocalcin, which plays a role in binding calcium to the bone matrix. In cardiovascular health, it supports proteins that inhibit arterial calcification, or the hardening of arteries.
Because K2 is less abundant in the typical Western diet than K1, incorporating foods like full-fat dairy and certain fermented products can help ensure adequate intake. A varied and balanced diet that includes both leafy greens and animal/fermented sources is the best way to get enough of both forms of vitamin K.
Conclusion
In conclusion, milk definitely contains vitamin K, but its presence and quantity are directly tied to its fat content. Whole milk is a source of vitamin K2, a form that is especially beneficial for bone and heart health, while skim milk contains very little. For those looking to increase their intake of this important nutrient, incorporating full-fat dairy products like milk, yogurt, and especially aged cheeses can be an effective strategy. However, a balanced diet rich in both plant-based K1 sources and K2-rich foods is the most comprehensive approach to meeting your vitamin K needs. For further information on recommended dietary intake, consulting health professionals or national health resources is advisable.
Visit the NIH Office of Dietary Supplements for more information
