What Exactly is Vitamin K?
Vitamin K isn't a single compound, but a family of structurally similar, fat-soluble vitamins. The two most important forms for human health are vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). The body stores vitamin K in tissues like the liver, brain, and heart, but it is rapidly broken down and excreted, meaning a continuous dietary supply is beneficial.
Vitamin K1 vs. Vitamin K2
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Source | Plant foods, especially green leafy vegetables. | Fermented foods and animal products like cheese, meat, and eggs. |
| Function | Primarily transported to the liver to help with blood clotting factors. | Transported to extra-hepatic tissues like bone and arteries. |
| Bioavailability | Absorbed less efficiently from food than K2. | Better bioavailability and longer half-life, especially MK-7. |
| Synthesis | Made by plants during photosynthesis. | Synthesized by bacteria in the gut, with gut flora converting some K1 to K2. |
The Crucial Functions of Vitamin K
This fat-soluble vitamin plays a vital, multifaceted role in human physiology. While its role in coagulation is most famous, it also supports skeletal and cardiovascular health through different mechanisms.
Supporting Blood Clotting
The most recognized function of vitamin K is its role as a cofactor for the gamma-glutamyl carboxylase enzyme, which activates specific proteins in the liver. These are the proteins required for blood coagulation, including factors II, VII, IX, and X. Without sufficient vitamin K, these clotting factors remain inactive, leading to impaired coagulation and an increased risk of excessive bleeding. This is why people taking blood-thinning medications like warfarin must monitor their vitamin K intake, as it can interfere with the drug's effectiveness.
Promoting Bone Health
Vitamin K is also an essential cofactor for proteins involved in bone metabolism. A prime example is osteocalcin, which is produced by osteoblasts and is crucial for binding calcium and regulating bone mineralization. Adequate vitamin K is needed to activate osteocalcin, allowing it to function properly. Research suggests that high levels of uncarboxylated osteocalcin (inactive) are a marker of poor vitamin K status and are associated with a higher risk of fractures and lower bone mineral density. While supplementation studies have shown mixed results, maintaining a good dietary intake is consistently linked with better bone health outcomes.
Protecting Cardiovascular Health
Emerging evidence links vitamin K to the prevention of arterial calcification, a key factor in cardiovascular disease. The vitamin K-dependent protein, matrix Gla protein (MGP), is responsible for inhibiting the calcification of soft tissues like blood vessels. Studies have shown that a higher intake of either vitamin K1 or K2 is associated with a lower risk of atherosclerotic cardiovascular disease events. The effectiveness of K2, particularly the MK-7 form, in being transported to extra-hepatic tissues like the arteries is of specific interest for this function.
Are We at Risk for Deficiency?
For most healthy adults with a balanced diet, vitamin K deficiency is rare. The vitamin is widely available in plant foods (K1), and gut bacteria produce K2. However, certain populations are at a much higher risk and require special attention.
High-Risk Groups for Vitamin K Deficiency
- Newborn Infants: All newborns are born with very little vitamin K, as it does not cross the placenta easily and is low in breast milk. This makes them highly susceptible to Vitamin K Deficiency Bleeding (VKDB), a serious and life-threatening condition. For this reason, a vitamin K shot is routinely given to newborns soon after birth.
- Malabsorption Conditions: Individuals with disorders that impair fat absorption, such as celiac disease, cystic fibrosis, or inflammatory bowel diseases, may struggle to absorb adequate vitamin K from their diet.
- Medication Users: People on certain medications, including long-term antibiotics or bile acid sequestrants, may have reduced vitamin K absorption or production.
- Severely Malnourished Individuals: Poor overall nutritional status can lead to deficiency, especially if the diet is very low in fat or lacks vitamin K-rich foods.
How to Get Enough Vitamin K
Since deficiency is uncommon in healthy adults, most people can meet their needs through a varied and balanced diet. The Adequate Intake (AI) for adult men is 120 mcg/day, and for women, it is 90 mcg/day.
Rich Dietary Sources of Vitamin K
- Vitamin K1: Green leafy vegetables are powerhouses of vitamin K1. Examples include kale, spinach, collard greens, broccoli, Brussels sprouts, and romaine lettuce. Other plant sources include vegetable oils like soybean and canola oil.
- Vitamin K2: Fermented soybeans (natto) are an exceptional source of K2 (MK-7). Other sources include eggs, cheese, meat, and fermented dairy products.
Conclusion
In summary, vitamin K is an absolutely essential nutrient for several vital bodily functions, especially blood clotting and bone health. While healthy adults consuming a balanced diet can often meet their needs, awareness of its role and food sources is important. For at-risk individuals, particularly newborns and those with malabsorption issues, vitamin K supplementation or medical intervention is crucial to prevent serious complications like uncontrolled bleeding. While the necessity for healthy adults to supplement is still under research, the evidence is clear that this often-overlooked nutrient is a fundamental component of a healthy diet, playing a bigger role than just wound healing.
