Understanding Vitamin K2 and Its Forms in Milk
Vitamin K is a fat-soluble nutrient family comprised of two primary forms: Vitamin K1 (phylloquinone), predominantly found in leafy green vegetables, and Vitamin K2 (menaquinone), found mainly in animal products and fermented foods. In dairy products, Vitamin K2 exists as a series of menaquinones (MK-n), which are distinguished by the length of their side chain. The most common forms found in plain milk are the longer-chain menaquinones, particularly MK-9, MK-10, and MK-11, which are thought to be produced by bacteria in the cow’s digestive system. Modest amounts of MK-4 are also present, which are converted from Vitamin K1 within the animal's tissues.
The Direct Correlation Between Milk Fat and Vitamin K2 Content
Research has repeatedly established that the amount of vitamin K2 in milk is strongly correlated with its fat content. Since Vitamin K2 is a fat-soluble vitamin, it is stored within the fatty portion of the milk, meaning that as the fat is removed, so is the majority of the K2. A USDA study from 2017 provided concrete figures, demonstrating the stark difference between fat content and K2 concentration in various milk types. For example, total vitamin K levels in full-fat (4%) milk were measured at 38.1 µg/100g, while nonfat milk contained just 7.7 µg/100g. This means that opting for skim or low-fat milk dramatically reduces your intake of this important nutrient.
Fermented Dairy: A More Potent Source
While plain milk does contain vitamin K2, it pales in comparison to the levels found in fermented dairy products like cheese and kefir. The fermentation process introduces beneficial bacteria that are highly effective at synthesizing various forms of menaquinones, significantly boosting the K2 content. Hard and blue cheeses, in particular, are exceptional sources, often containing higher concentrations of the longer-chain MKs. Kefir, a fermented milk drink, has also been shown to contain appreciable amounts of K2.
Comparison Table: Vitamin K2 Content in Dairy
| Dairy Product | Fat Content | Typical Vitamin K2 Content (μg/100g) | Notes |
|---|---|---|---|
| Full-Fat Milk | ~4% | Modest (e.g., 38.1 µg total K) | Content strongly depends on fat concentration. |
| 2% Reduced-Fat Milk | ~2% | Low to Modest (e.g., 19.4 µg total K) | Significantly less than full-fat versions. |
| Nonfat (Skim) Milk | <1% | Very Low (e.g., 7.7 µg total K) | Contains only residual amounts. |
| Hard Cheeses (e.g., Gouda, Edam) | Varies | High (e.g., 30-50 µg MK-9) | Levels depend on bacteria and aging. |
| Blue Cheese | Varies | Very High (up to 49 μg MK-7) | Produced with specific bacterial cultures. |
| Kefir (fermented milk) | Varies | Moderate to High (up to 4.8 μg MK-7) | Levels influenced by specific kefir grains. |
| Butter | ~80% | Moderate (e.g., 15 μg MK-4) | Good source due to high fat content. |
Health Benefits of Vitamin K2 in Dairy
The vitamin K2 found in milk and other dairy products provides important health benefits, primarily associated with bone and cardiovascular health. It activates specific proteins, such as osteocalcin and Matrix Gla-protein (MGP), that regulate calcium metabolism in the body. Activated osteocalcin helps bind calcium to the bone matrix, promoting bone mineralization and strength. At the same time, activated MGP prevents calcium from depositing in soft tissues like arteries, which helps maintain vascular elasticity and reduces the risk of heart disease. A balanced intake of Vitamin K2, alongside Vitamin D and calcium, is critical for effective calcium utilization, preventing potential negative health outcomes from excessive calcium deposits in the wrong places.
What Influences K2 Content in Milk?
Aside from the fat content and fermentation, other factors can influence the vitamin K2 levels in dairy products. The diet and living conditions of the dairy cow play a role. Grass-fed cows, for instance, are believed to produce milk with higher vitamin K levels than conventionally fed cows, although this can be subject to seasonal variation. The processing of milk, including pasteurization, does not directly destroy K2, but the bacterial cultures and aging process used in creating products like cheese are key factors in elevating menaquinone levels. Differences in regional production methods, starter cultures, and maturation times are responsible for the wide variance in K2 content observed in different cheese types across the globe. The specific menaquinone profile (e.g., MK-4 vs. MK-9) also depends on the production process and the bacterial strains involved.
Conclusion
So, is vitamin K2 present in milk? Yes, it is, but its presence is directly tied to the product's fat content. While full-fat milk offers a modest amount, the richest dairy sources of vitamin K2 are fermented products like aged cheeses and kefir, where bacterial action significantly boosts menaquinone levels. For those looking to increase their dietary intake of Vitamin K2, incorporating fermented and full-fat dairy products can be an effective strategy. However, relying solely on unfermented milk will provide only limited amounts. Understanding these distinctions allows consumers to make informed choices about their nutritional intake and harness the significant bone and heart health benefits that vitamin K2 offers. Read more about the benefits and different functions of Vitamin K1 vs K2 here.
