Vitamin K (VK) is a fat-soluble vitamin primarily recognized for its function in regulating blood clotting (coagulation), which prevents excessive bleeding following injury. Beyond this well-known role, emerging research highlights a relationship between adequate Vitamin K status and the long-term health of highly vascularized tissues, including the eyes. Because the visual system relies on a complex network of blood vessels for nourishment, Vitamin K may play a significant part in preserving vision.
Vitamin K’s Role in Ocular Vascular Health
The eye contains some of the body’s most delicate and densely packed blood vessels, particularly within the retina and choroid, which supply oxygen and nutrients. Maintaining the integrity and flexibility of these tiny vessels is essential for sustaining clear vision. Vitamin K supports this microvascular environment by participating in the activation of specific proteins found throughout the eye’s tissues.
Poor Vitamin K status has been linked to ocular issues involving vascular compromise. Severe deficiency can contribute to retinal hemorrhaging, where bleeding occurs from weakened blood vessels due to impaired clotting factors. Vitamin K’s influence on vascular health is also being investigated for its protective effect against Age-Related Macular Degeneration (AMD), a disease associated with chronic vascular stress and inflammation.
Newer studies suggest that a non-canonical pathway involving Vitamin K may protect retinal cells from ferroptosis, a type of cell death. This mechanism, independent of the vitamin’s classic coagulation role, provides an additional defense for the eye’s light-sensitive tissues. Adequate Vitamin K intake supports the overall structure and function of the eye’s intricate circulatory system, helping to minimize damage.
Understanding Coagulation and Calcification Prevention
The systemic benefits of Vitamin K stem from its function as a cofactor for an enzyme that modifies specific proteins, known as Vitamin K-dependent proteins (Gla proteins). This modification, called gamma-carboxylation, is necessary to make these proteins biologically active. The two main forms, K1 (phylloquinone) and K2 (menaquinones), share this core function but differ in their primary sites of action.
Vitamin K1 mainly activates coagulation factors produced in the liver, which are responsible for forming blood clots. Vitamin K2 primarily activates extrahepatic proteins (those found outside the liver) crucial for regulating calcium distribution. One important extrahepatic protein is Matrix Gla Protein (MGP).
When activated by Vitamin K2, MGP inhibits soft tissue calcification, preventing calcium buildup in the walls of arteries and veins. This is relevant for the tiny blood vessels supplying the eye, as calcification can restrict blood flow to the retina. K2’s ability to direct calcium away from soft tissues promotes long-term vascular flexibility and supports the fragile microcirculation of the eye. Unlike K1, which is concentrated in the liver and has a shorter half-life, the K2 form (especially menaquinone-7 or MK-7) remains in circulation longer, enhancing these extrahepatic functions.
Obtaining Adequate Vitamin K Through Diet
Meeting the body’s need for Vitamin K requires a balanced intake of both K1 and K2 forms from various food sources. The Adequate Intake (AI) for Vitamin K in adults is 120 micrograms (mcg) per day for men and 90 mcg per day for women. Most people obtain the majority of their Vitamin K from K1, which is abundant in green leafy vegetables.
Excellent sources of Vitamin K1 (phylloquinone) include:
- Kale
- Spinach
- Collard greens
- Turnip greens
- Broccoli
Since Vitamin K is fat-soluble, consuming these vegetables with a small amount of fat, such as olive oil, can enhance absorption.
Sources for Vitamin K2 (menaquinones) are less common in the typical Western diet, as they are primarily found in fermented foods and certain animal products. The best-known source is Natto (fermented soybeans), which is rich in the highly bioavailable MK-7 form. Other dietary sources of K2 include certain cheeses, egg yolks, and organ meats. Individuals taking blood-thinning medications like warfarin must maintain a consistent daily intake of Vitamin K to avoid interfering with their medication’s effectiveness, and should consult a physician regarding dietary changes.