Vitamin K is an essential micronutrient found in certain foods and nutritional supplements. Best known for its critical role in blood platelet function, this compound owes its common name to the German term, "Koagulationsvitamin." Two basic forms of vitamin K -- K1 and K2 -- are used in medicine and human nutrition. Although the body derives similar benefits from both compounds, only K1 is sold in over-the-counter supplements in the United States. The two forms of vitamin K differ slightly in their origins, safety and functions.
Sources and Origins
Vitamins K1 and K2 vary in their natural and synthetic origins. Although both are made synthetically for use in supplements and fortified foods, they are also available naturally as part of a balanced diet. Natural sources of vitamin K1 include green vegetables such as broccoli, spinach, turnip greens, collards, lettuce, asparagus and avocado. Most diets supply significantly lower levels of K2, which occurs in small amounts in dairy products and certain fermented food. Bacteria in the human colon also produce some vitamin K2.
Sub-Types and Synthetic Forms
Nutritionists and health care providers further classify vitamins K1 and K2 into narrower subtypes. Vitamin K1 is known as phylloquinone in its natural, plant-based form. The synthetic form of the compound, phytonadione, is most commonly used in nutritional supplements and medications. Both offer similar benefits. Vitamin K2 compounds, known as menaquinones, or MKs, occur as MK4 and MK7. MK4 exists naturally in meats, eggs and dairy products, while MK7 occurs as a byproduct of certain bacteria.
Benefits and Indications
Although all forms of vitamin K ultimately provide similar benefits and risks to the human body, K1 and K2 vary slightly in their clinical indications. K1 and K2 both work to prevent vitamin K deficiency, a serious but rare condition that can cause life-threatening hemorrhage. They may also help reduce osteoporosis symptoms and bruising. Both forms of vitamin K can help reverse the effects of warfarin, a potent anticoagulant, or blood thinner.
Safety and Risks
Only vitamin K1 is sold in the United States as a nutritional supplement. K1 is regarded as more absorbable, faster-working and less toxic than K2. The human body absorbs K2 more slowly and it tends to linger longer in the system. For this reason, the American Cancer Society warns against the use of foods containing K2 for people taking blood thinners. Too much of either form could inhibit the actions of these drugs or lead to fatal blood clots. Always consult a health care provider before using any nutritional supplement, particularly if you are taking medication.