The Two Forms of Vitamin K
Vitamin K is a fat-soluble nutrient essential for several bodily functions, including blood clotting and bone metabolism. However, it exists in two primary forms with different dietary sources and functions:
- Vitamin K1 (Phylloquinone): This form is primarily found in plant-based foods, such as green leafy vegetables like kale, spinach, and broccoli.
- Vitamin K2 (Menaquinones): This form is mainly found in animal-based and fermented foods, including meat, eggs, and dairy products. Different sub-types of menaquinones (e.g., MK-4, MK-7, MK-9) are produced by bacteria.
When we discuss whether we can get vitamin K from milk, we are almost exclusively talking about the menaquinone, or K2, form. The amount of vitamin K1 in milk is negligible.
Milk Fat and Vitamin K Content
Because vitamin K is a fat-soluble vitamin, its concentration in milk is directly tied to the fat content. This means that the more fat the milk contains, the higher its vitamin K2 levels will be. Research has explicitly confirmed this, showing a dramatic difference in content between full-fat and reduced-fat dairy products.
A 2017 study by Fu et al. provided a detailed breakdown of vitamin K content in various milk products. The findings highlight the significant impact of fat removal during processing:
- Full-fat milk (4% fat): Contained the highest levels of total vitamin K, with appreciable amounts of menaquinones (MK9, MK10, MK11).
- 2% milk: Had significantly lower concentrations of total vitamin K compared to full-fat milk.
- 1% and fat-free milk: Contained very little to no detectable vitamin K, as the fat removal process eliminates the vitamin.
This evidence clarifies that for individuals relying on milk as a source of vitamin K2, choosing full-fat milk is essential. The practice of removing fat for low-calorie alternatives comes at the expense of this vital nutrient.
The Role of the Cow's Diet and Microbes
The vitamin K2 found in milk doesn't just appear out of nowhere; it is a result of the cow's diet and its unique digestive system. Studies have shown that the menaquinones in non-fermented products like milk originate, at least in part, from bacterial processes within the cow's ruminant gut. Furthermore, the cow's diet can influence the vitamin K content of its milk. For example, milk from pasture-fed cows, especially during summer grazing, has been found to have higher levels of both K1 and K2.
Comparison of Dairy Vitamin K Sources
While milk is a source of vitamin K2, it's not the only dairy product that provides it. Fermented dairy products like yogurt and cheese, which involve bacterial cultures, can also be excellent sources. The fermentation process can significantly boost the K2 content. The specific bacteria used and the ripening process can lead to significant variation in K2 content between different cheese varieties.
Here's a comparison of vitamin K concentrations in different dairy products and other foods:
| Food Item (per 100g) | Primary Vitamin K Type | Vitamin K Content (μg/100g) | Notes |
|---|---|---|---|
| Full-fat Milk | K2 (Menaquinones) | ~38.1 | Levels decrease significantly with fat removal. |
| Full-fat Yogurt | K2 (Menaquinones) | Similar to full-fat milk | Fermentation can add more K2. |
| Natto (Fermented Soybeans) | K2 (MK-7) | ~998 (per 100g) | Extremely rich source of K2. |
| Gouda Cheese | K2 (Menaquinones) | ~47-73 | A very rich fermented dairy source. |
| Cheddar Cheese | K2 (Menaquinones) | ~8.6-23.5 | Varies by aging and production. |
| Spinach (raw) | K1 (Phylloquinone) | ~400 | Excellent plant-based source of K1. |
| Broccoli (raw) | K1 (Phylloquinone) | ~100 | Good plant-based source of K1. |
The Significance of Vitamin K2 for Health
Recent research has highlighted the unique and important functions of vitamin K2, distinct from K1. While K1 is primarily involved in blood clotting, K2 plays a key role in supporting bone and cardiovascular health. For instance, K2 helps regulate calcium, directing it to the bones where it is needed and preventing its buildup in soft tissues like arteries, which can lead to calcification. This has led to growing interest in dietary sources of K2, making the content in dairy products a subject of increasing focus.
Conclusion
Can you get vitamin K from milk? Yes, you can, but it is important to be aware of the specifics. Milk, particularly full-fat varieties, provides a source of vitamin K2, a form with distinct health benefits for bone and cardiovascular health. However, milk's vitamin K contribution is directly linked to its fat content, with low-fat and fat-free versions offering minimal amounts. Compared to other foods like natto or certain aged cheeses, milk is not the most concentrated source, but it remains a valuable part of a balanced diet. Individuals aiming to maximize their vitamin K intake should consider a variety of sources, including leafy greens for K1 and fermented dairy products for additional K2. Understanding the difference in vitamin K forms and their sources is key to making informed nutritional choices for overall health. A good resource for further reading is the NIH Office of Dietary Supplements Vitamin K Fact Sheet.
