What is Vitamin K2 and Where Does It Come From?
Vitamin K is a fat-soluble vitamin primarily known for its role in blood clotting. It exists in two main forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinone). While K1 is abundant in leafy green vegetables like spinach and kale, K2 is largely synthesized by bacteria and found in fermented foods and animal products. Different bacterial strains can produce varying lengths of K2 molecules, or menaquinones (MK-n), such as MK-4 and MK-7, which are the most studied.
The bacteria used in fermentation for foods like cheese and yogurt are responsible for synthesizing K2. The specific bacterial strains, the fermentation duration, and the fat content of the dairy all influence the final K2 concentration in the product. In fact, certain mesophilic starter cultures used for cheesemaking can produce significantly more menaquinones than the thermophilic cultures typically found in standard yogurt. This is why the K2 content in dairy can be so variable, and yogurt is not necessarily a top source compared to some cheeses.
The Role of Fat Content in Yogurt's K2 Levels
One of the most important factors determining the K2 content in yogurt is its fat content. As a fat-soluble vitamin, K2 is concentrated in the fatty parts of dairy products. Numerous studies have confirmed that full-fat dairy products, including yogurt, contain substantially more vitamin K2 than reduced-fat or fat-free versions. A recent US study showed that reduced-fat or fat-free dairy products contained only 5–22% of the K2 content found in full-fat dairy. This is also why many fortified yogurts deliver K2 in a full-fat or enriched-fat matrix to ensure bioavailability.
For optimal absorption, it is always recommended to consume vitamin K, both K1 and K2, with a meal that contains some fat. This is because bile acids, released to aid fat digestion, are necessary for the absorption of fat-soluble vitamins.
Factors Affecting K2 Content in Yogurt
Beyond fat content, several other elements play a crucial role in how much vitamin K2 your yogurt actually contains:
- Starter Cultures: Different lactic acid bacteria (LAB) strains and other bacteria used for fermentation produce different types and amounts of menaquinones. Some cultures, such as those used for specific cheeses, are known to be far more productive K2 synthesizers than others.
- Fermentation Process: The duration and specific conditions of the fermentation process can influence bacterial activity and, consequently, K2 production.
- Animal Feed: The diet of the dairy animal also plays a role. Dairy products from grass-fed cows, for instance, can contain higher levels of MK-4, a subtype of K2.
- Fortification: Some brands actively fortify their yogurt with vitamin K2, often in the form of MK-7, to increase its nutritional value. This is a key distinction from naturally occurring K2 and will be clearly listed in the ingredients.
Comparison: Yogurt vs. Other K2 Sources
While yogurt is a source of K2, it is not the most concentrated. The content can also vary significantly. Here is a comparison of typical K2 content across different foods:
| Food Source | K2 Content (per 100g) | Primary K2 Form | Notes |
|---|---|---|---|
| Natto (Fermented Soybeans) | 998-1100 mcg | MK-7 | The richest known dietary source, but has a strong taste. |
| Hard Cheeses (e.g., Gouda) | 76 mcg | MK-8, MK-9 | Very rich source due to specific bacterial cultures and long fermentation. |
| Soft Cheeses (e.g., Brie) | 56 mcg | MK-8, MK-9 | Also a good source, with K2 developing during the ripening process. |
| Chicken Breast | 10-13 mcg | MK-4 | A solid source of MK-4, more readily available than organ meats. |
| Full-Fat Yogurt | 0-2 mcg | MK-9, MK-10, MK-11 | Contains some K2, but highly variable depending on brand and cultures. |
| Skimmed Yogurt | Negligible to none | None | The fat-soluble K2 is removed during the processing. |
| Fermented Milk (Kefir) | Up to 13 mcg | MK-4, MK-7, MK-9 | Often contains higher amounts than standard yogurt due to different starter cultures. |
Is Yogurt a Sufficient Source for Your K2 Needs?
Given the variability and generally lower concentrations compared to powerhouse sources like natto or certain cheeses, yogurt alone may not be a sufficient or reliable source to meet daily vitamin K2 needs, especially for those with low K2 status. For most Western diets, which tend to be deficient in K2, getting enough from regular diet, even including dairy, can be a challenge.
For those who enjoy yogurt, choosing full-fat varieties will provide a modest boost of K2 along with beneficial probiotics. However, combining a variety of K2-rich foods—like fermented cheeses, pasture-raised eggs, and organ meats—offers a more robust dietary strategy. For individuals with specific health needs, including those with osteoporosis or cardiovascular concerns, or those on blood thinners, consulting a healthcare provider about their vitamin K intake and potential supplementation is advisable.
Conclusion
Yes, yogurt contains vitamin K2, but its presence is highly dependent on factors such as fat content and the specific bacterial cultures used during fermentation. To get the most K2 from yogurt, opt for full-fat, traditionally fermented versions. However, it's not the richest source available, and for those aiming to significantly boost their K2 intake, other options like fermented cheeses, kefir, or natto are more potent. A balanced diet incorporating various K2 sources, especially alongside healthy fats, is the most effective approach. For reliable, consistent amounts, some may benefit from fortified products or supplements after medical consultation.
