The Relationship Between Dairy and Vitamin K2
Vitamin K is a fat-soluble vitamin and an essential cofactor for several proteins involved in blood clotting and bone metabolism. It exists in two primary forms: vitamin K1 (phylloquinone), found mainly in plants, and vitamin K2 (menaquinones), produced by bacteria and found in fermented and animal-based products. Milk's contribution to vitamin K2 intake, therefore, depends heavily on its composition and processing.
Full-Fat vs. Skim Milk
Given that vitamin K is fat-soluble, its concentration is directly proportional to a dairy product's fat content. In a study that measured vitamin K concentrations in various dairy products, full-fat (4% fat) milk was shown to have a much higher total vitamin K content than 2%, 1%, or fat-free versions. This is because the menaquinones (vitamin K2) are stored within the milk fat globules. The skimming process removes this fat, stripping the milk of most of its vitamin K2 content.
The Impact of Grass-Feeding and Pasteurization
What a cow eats also affects the nutritional profile of its milk. Cows fed primarily on grass produce milk with higher levels of fat-soluble vitamins, including K2. This is because grass is a rich source of vitamin K1, which the cow's digestive system can convert to the more bioavailable MK-4 form of vitamin K2. Conversely, pasteurization and ultra-pasteurization, while ensuring safety, can degrade some vitamins and enzymes in milk. Raw milk from pastured cows is often touted as having higher K2 content, though this is also dependent on the season and the soil quality of the farm.
Fermentation: The Game-Changer for K2
While regular milk offers modest amounts of K2, the real powerhouse sources from dairy are fermented products. Certain lactic acid bacteria used as starter cultures for dairy fermentation are potent producers of menaquinones. This bacterial synthesis significantly boosts the K2 concentration in the final product. For instance, hard and soft cheeses and kefir are consistently noted as excellent sources of various menaquinones (MK-4, MK-8, MK-9).
Other Food Sources of Vitamin K2
To get a balanced perspective, it is helpful to compare milk's K2 content to other dietary sources. Here is a comparison of K2 levels in common foods:
| Food Source | K2 Content (per 100g, approx.) | Primary MK Type | Notes |
|---|---|---|---|
| Natto (fermented soybeans) | 1,000 mcg | MK-7 | Exceptionally high concentration |
| Goose Liver Pâté | 369 mcg | MK-4 | Rich, but not a daily food |
| Gouda/Hard Cheeses | ~76 mcg | MK-9 | Excellent source from fermentation |
| Soft Fermented Cheeses (e.g., Brie) | ~57 mcg | MK-9 | Solid source with other benefits |
| Egg Yolks (pastured) | ~15-30 mcg | MK-4 | Content varies with feed |
| Butter (grass-fed) | ~15 mcg | MK-4 | Also varies with cow's diet |
| Kefir (fermented milk) | ~5-10 mcg | MK-7 | Levels increase with fermentation |
| Whole Milk | ~1 mcg | MK-4/MK-9 | Lower concentration, but widely consumed |
The Health Benefits of Vitamin K2
Why is all this K2 discussion so important? Beyond its classic role in blood coagulation, K2 is vital for bone and cardiovascular health. It helps regulate calcium, directing it towards bones and teeth while preventing its buildup in soft tissues like arteries, which can lead to cardiovascular disease. Some studies have even linked higher K2 intake to a reduced risk of certain cancers, though more research is needed. Given its benefits, optimizing K2 intake is a sensible goal, and dairy can certainly play a role.
Conclusion: Milk's Role in K2 Intake
In summary, while regular whole milk does contain vitamin K2, it is not considered a high source, especially when compared to other foods like natto or certain cheeses. The K2 content in milk is highly dependent on its fat content and the cow's diet, with grass-fed, full-fat versions offering more. The most significant dairy sources of K2 come from fermented products like cheese and kefir, where bacterial action synthesizes higher concentrations of menaquinones. To ensure adequate intake, a diversified diet incorporating fermented foods, grass-fed dairy, and other animal products is the most effective strategy. While milk is a contributor, it should not be relied upon as the sole or primary source of this critical vitamin.
How to Maximize K2 from Dairy
If you want to maximize your vitamin K2 intake from dairy, follow these tips:
- Choose full-fat options: Always opt for whole milk over skim or low-fat versions, as K2 is fat-soluble and removed during the skimming process.
- Look for grass-fed: Whenever possible, select dairy products from cows fed on pasture. Their milk has higher K2 content due to their diet being rich in K1, which is converted to K2.
- Prioritize fermented dairy: Make cheese and kefir staples in your diet. Hard cheeses like Gouda and soft, aged cheeses are excellent sources of different MK forms.
- Seek raw milk (if safe): Some advocates suggest raw milk has higher K2 due to less processing, but this must be approached with caution due to potential health risks. Only consider this if sourced safely from reputable farms.
- Consider seasonal variations: Be aware that K2 levels in dairy can fluctuate based on the season, as a cow's diet changes. Look for butter with a deeper yellow color, which often indicates a higher nutrient content.
