The Vitamin K Family: K1 vs. K2
To understand the relationship between K2 and K7, it is first necessary to grasp the full vitamin K picture. Vitamin K is a fat-soluble vitamin and a family of compounds, not a single nutrient. The two primary natural forms are:
- Vitamin K1 (Phylloquinone): Primarily sourced from plants, such as leafy green vegetables like kale, spinach, and broccoli. Its main function is to activate proteins in the liver responsible for blood coagulation, or clotting.
- Vitamin K2 (Menaquinones): This group of compounds is produced by bacteria and found in certain animal products and fermented foods. Unlike K1, K2 plays a more crucial role in calcium metabolism outside of the liver, supporting bone and cardiovascular health.
Menaquinones: The Different Forms of Vitamin K2
Vitamin K2 is further categorized into subtypes called menaquinones, or MK-n, based on the length of their side chain. The number 'n' refers to the number of repeating isoprenoid units in the side chain. The most common and well-researched subtypes are menaquinone-4 (MK-4) and menaquinone-7 (MK-7), which is what people mean when they refer to K7.
Is K2 the same as K7? The Critical Distinction
It is inaccurate to say that K2 is the same as K7, as K7 (MK-7) is a specific member of the K2 family, not the entire group. This is similar to how a grapefruit is a type of citrus fruit, but is not the same as a lemon or the entire citrus family. The distinction is vital for understanding their different functions, especially in supplementation.
Key Functional Differences: MK-4 vs. MK-7
MK-4 and MK-7 are not interchangeable and have significantly different pharmacokinetic properties in the body, primarily due to their different chemical structures.
- Source: MK-4 is found in animal products like egg yolks, butter, and organ meats. It can also be converted in the body from K1. MK-7 is produced by bacteria during fermentation and is found in high concentrations in natto (fermented soybeans).
- Bioavailability and Half-Life: This is a crucial difference. MK-4 has a very short half-life of only a few hours and does not significantly increase blood serum levels after absorption. MK-7, with its longer side chain, has a much longer half-life (around 72 hours), allowing it to accumulate in the bloodstream and circulate longer throughout the body.
- Tissue Distribution: Because of its short half-life, MK-4 tends to be utilized primarily by the liver for blood clotting, while MK-7's prolonged circulation makes it more available for extrahepatic tissues, such as bones and blood vessels.
- Efficacy: The longer side chain and higher bioavailability of MK-7 generally make it the preferred form for targeting bone and cardiovascular health with smaller, once-daily doses. MK-4 requires much larger, more frequent doses for therapeutic effects, as is common in Japan for osteoporosis treatment.
The Role of K2 in the Body
Vitamin K2's main function is to activate vitamin K-dependent proteins (VKDPs) through a process called carboxylation. These VKDPs regulate where calcium is deposited in the body.
Two vital proteins that K2 activates are:
- Osteocalcin: This protein, produced by bone-building cells, binds calcium to the bone matrix, promoting stronger and denser bones.
- Matrix Gla Protein (MGP): Found in blood vessels and other soft tissues, MGP helps prevent calcium from accumulating in these areas.
Without sufficient K2, these proteins remain inactive, and calcium may be deposited in arteries instead of bones, which can contribute to cardiovascular issues.
Comparing K2 Subtypes: MK-4 vs. MK-7
| Feature | Menaquinone-4 (MK-4) | Menaquinone-7 (MK-7) |
|---|---|---|
| Side Chain | Shorter | Longer |
| Source | Animal products (butter, egg yolks, organ meats) | Fermented foods (natto), bacterial synthesis |
| Half-Life | Short (cleared in hours) | Long (circulates for days) |
| Bioavailability | Lower, does not significantly raise serum levels | Higher, accumulates in the bloodstream |
| Primary Function | Primarily utilized by the liver for clotting | Wide tissue distribution; targets bones and arteries |
| Dosage | Requires higher, more frequent doses for efficacy | Effective at lower, once-daily doses |
Food Sources of K2 Subtypes
Knowing the difference between MK-4 and MK-7 also helps in making informed dietary choices. Many Western diets contain low levels of K2, particularly the long-chain MK-7.
- MK-4 Rich Foods:
- Egg yolks
- Butter
- Organ meats, such as chicken liver
- Certain cheeses
- MK-7 Rich Foods:
- Natto (fermented soybeans) is the richest source.
- Hard cheeses like Gouda
- Soft cheeses like curd
- Sauerkraut
Since it can be difficult to get sufficient MK-7 from diet alone, especially in Western countries where natto is not a staple, supplements are a popular option.
Conclusion: K7's Superior Bioavailability Makes the Difference
The answer to the question "Is K2 the same as K7?" is a definitive no. K2 is the family of menaquinones, while K7 (MK-7) is one specific, superior subtype. While both MK-4 and MK-7 perform important functions in the body, their chemical structures lead to significant differences in bioavailability, half-life, and how effectively they reach extrahepatic tissues like bones and arteries. MK-7's longer half-life allows it to accumulate in the bloodstream, providing consistent activation of proteins vital for robust bone and cardiovascular health at smaller, more convenient dosages. Therefore, for individuals looking to support their bone density and prevent arterial calcification, prioritizing MK-7 through diet or supplementation is the more effective strategy.
