From George Mateljan: Vitamin K

I have been getting a lot of questions from our Readers about vitamin K, so this week I wanted, once again, to share this overview of vitamin K with you. Over the past 20 years, no vitamin family has undergone a greater change in terms of our scientific understanding of its chemistry and function.

Vitamin K has been finding its way back into the nutrition spotlight, and for good reason. In the past, we've traditionally focused on this fat-soluble vitamin as a blood-clotting agent. When we are injured, we cannot stop the bleeding unless our blood can coagulate and form a clot to help seal off the wound. The proteins we need to accomplish this task cannot be recruited into action without vitamin K. (The very name of this vitamin originally came from the German word koagulation.)

Beyond Blood Clotting
More recently, researchers have determined that this role played by vitamin K in coagulation is only one of its key functions. Just as important is the role it plays in bone health since it is necessary for our bones to properly mineralize. In fact, there is good evidence to show that vitamin K can be helpful in both prevention and treatment of osteoporosis (loss of bone mineral density). Vitamin K may also play an important role in heart health since it prevents excess depositing of calcium in our arteries, a condition called arterial calcification that can lead to hardening of the arteries. (While there is not yet an abundance of research showing vitamin K to help prevent or treat hardening of the arteries, this area of research is still a very active one.) Cystic fibrosis, atherosclerosis, and several types of cancer are also conditions that are actively being investigated for possible links with vitamin K deficiency.

The K1 versus K2 Controversy
Along with the wealth of new research on vitamin K described above has come a controversy over the health benefits provided by different forms of vitamin K. Traditionally, research in this area focused the phylloquinones (K1) and their benefits for healthy blood clotting. Along with this focus has come a recommendation for more green leafy vegetables in the diet since these foods are top sources of K1. Olive oil is also a key source for dietary K1. The vast majority of vitamin K in our diet comes from the K1 in vegetables and vegetable oils.

K1 is not the only form of vitamin K found in food, however, and it is not the form of vitamin K best able to support healthy bone. For optimal support in this area of our health, we need K2.

As K2 is better at bone support than K1, a controversy has arisen over dietary approaches to adequate vitamin K intake and also over the issue of diet versus supplements for optimal vitamin K support. It is definitely possible for us to obtain K2 from food: our best dietary sources of this form of the nutrient are meats, eggs, and fermented foods including cheese, curd, and fermented soy products. (Since Bacillus natto are bacteria that can convert K1 into K2 and these bacteria are often involved in the production of fermented soy products, you will sometimes find the word "natto" being used to refer to these foods.)

From a practical standpoint, we may or may not eat enough of these foods to get optimal K2 intake. In studies on women in Japan, the intake of fermented soy foods appears to be very important in providing them with ample K2 intake in their diet. If you are a person who does not eat any of the foods described above, you can still obtain K2, but in this case, you are depending on the bacteria in your digestive tract or metabolic events in your cells to take the K1 content of your food and convert it into K2. Under healthy circumstances, the bacteria in your digestive tract and the enzymes in your cells may be able to keep an optimal balance between the K1 and K2 forms of this vitamin.

But under other circumstances, an optimal balance may not be possible. One of these circumstances under active research investigation is aging, and especially aging as it occurs in postmenopausal women. Other circumstances include liver problems and problems with fat absorption. If any of these circumstances apply to you, you should consult with your healthcare provider to work out an optimal approach to vitamin K.

The MK-4 versus MK-7 Controversy
Gut bacteria, cell metabolism, and foods can provide us with several different forms of K2. The best studied of these forms are MK-4 (menaquinone 4) and MK-7 (menaquinone 7). Meats and eggs are our most common food sources of MK-4. Fermented soy foods are our most common source of MK-7. Remember that both MK-4 and MK-7 are forms of K2 and both are helpful when it comes to bone support. We suspect that within this vitamin K2 area, the right amount of MK-4 and MK-7 is an amount that can vary from moment to moment and from individual to individual. From a research perspective, we also believe that the jury is still out on these specific forms of K2 and their best mix in the diet.

Vitamin K3
Although our bodies may regularly use vitamin K3 (menadione) as a transport form for vitamin K or for excretion of this vitamin out of the body, vitamin K3 is not found preformed in food in significant amounts. It is also not allowed as a form of vitamin K in dietary supplements. You don't need to worry about this form of vitamin K from a dietary standpoint.

Types of Vitamin K--A Quick Summary
Below is a table that summarizes the information described above:

Food Sources of Vitamin K and Practical Dietary Steps
Along with the green leafy vegetables mentioned earlier (especially kale, chard, mustard greens, turnip greens, and spinach), your best food sources of vitamin K include: parsley, broccoli, leaf lettuce, romaine lettuce, endive, cabbage, cauliflower, watercress, eggs, meats, cheeses, curd, and fermented soybean products.

If you do not consume plentiful amounts of the plant foods listed above, you may be at risk not only for vitamin K1 deficiency, but for K2 deficiency as well since your body will not have enough K1 to convert into K2. Even if you do include meat, eggs, or cheese in your diet, you may still not be getting enough vitamin K2 in your diet (since life stage and health considerations.like aging and postmenopausal status.confer special needs), but that issue involves your personal health situation and needs to be discussed with your healthcare provider.

To boost your overall vitamin K nourishment, we recommend that you focus as much as possible on the green leafy vegetables that are such outstanding sources of K1. Overdoing it with animal foods is not a good way to try and balance your overall vitamin K status or offset a vitamin K2 deficiency because it will put you at too great a risk for other dietary imbalances. Fermented soy products are your best way to try to improve your K2 intake if you want to focus on this form of vitamin K.

Can I Get Too Much Vitamin K?
Most people are not going to get too much vitamin K from their diet under any circumstance and in any form. An exception involves individuals who are taking warfarin (a prescription drug more commonly referred to by its brand name, Coumadin®). This medication is given to help block the activity of vitamin K and slow down the process of clot formation. Coumadin® is often prescribed for individuals who are at risk of forming blood clots too quickly or too easily. If you are taking this medication, or have a history of problems related to blood clotting, you should follow your doctor's instructions about diet and vitamin K-containing foods since you are likely to need restriction of vitamin K-rich foods in your diet.

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