If you have ever been on a blood thinner medication like Warfarin or know someone who has, then it is likely that you’ve heard of vitamin K. You may have heard it is advised to avoid foods rich in vitamin K, or to be “consistent” in the amount and times you eat vitamin K-rich foods (like leafy greens).
Vitamin K is a fat-soluble vitamin. There are several forms of vitamin K. The two main families are: vitamin K1 and vitamin K2 (phylloquinone and menaquinones also referred to as “MKs” or K2 respectively).
Of the vitamin Ks found in nature, the most bioavailable form for our bodies seems to be the menaquinone (vitamin K2-7 or MK-7) form. However, this happens to be the form that we get the least of in the Western diet. It is estimated that up to 80% of Americans have suboptimal levels of vitamin K2.
While vitamin K1 is absorbed and used primarily by the liver, vitamin K2 (MK-7) is available, and measurable, in serum blood. As such, unlike vitamin K1, vitamin K2 does not get sequestered in the liver for only the liver’s function. Rather, because it is available in serum blood, it can travel to and go to work in other areas of the body.
Why is this important?
Vitamin K2 plays an important role in a number of physiological functions. For example, it supports many enzymatic activities such as:
- being cardio-protective (multiple study results found it protects the heart)
- helping to build and maintain strong bones (a deficiency of vitamin K can lead to bone fractures and osteoporosis)
- supports anti-cancer properties
- enhancing athletic performance by increasing cardiac output when serum stores are optimal
- preventing blood vessel mineralization (helps move calcium out of blood vessels, prevent calcium plaque buildup, and puts it in places where it belongs, like bone)
- supporting joint health
- supporting GI microbiome health
- protecting against vascular dementia
- helping people with diabetes, and preventing and reducing neurodegenerative diseases/neuropathies
- playing a role in magnesium and vitamin D metabolism
- supporting healthy aging through its protective actions in mitochondrial health
O.K., you get the picture!
How much do I need?
The Adequate Intake (AI) level for women is 90 ug/day and for men is 120ug/day.
The Adequate Intake levels assume that your baseline stores are intact. For individuals with depleted vitamin K stores, the needs are higher.
Each one of us is unique. Some studies have suggested optimal doses for repletion and/or maintenance can be up to 300 ug/day (depending on individuals’ needs) taken in divided doses throughout the day until stores are replete.
It is best absorbed when either taking a K-2 supplement, either taken by itself or with its co-factors (like zinc, magnesium, boron). For optimal absorption, we want to make sure other mineral stores within the body are adequate.
Assessing your diet and your personal needs is an important place to start to determine what your vitamin K needs are. For most of us, supplementation might be the best method.
How to get it in your diet
While individuals who eat an abundant amount of leafy greens like chard, kale, and spinach (3-5 cups of raw or 1.5-3 cups of cooked leafy greens a day) get good sources of vitamin K1, it is likely K-2 is lacking as vitamin K-2 is not readily available in the Western diet. There are synthetic sources of vitamin K available (MK-4 for example). However, synthetic sources of K are less bioavailable. The most notable food source of vitamin K-2 is Natto, a fermented food found in Eastern Japan. This is available in some health food and Asian markets here in the U.S. My daughter, who is currently living and studying in Eastern Japan, has had the benefit of eating this daily with breakfast. Although, she reports, as do many others, it is a taste that takes some time getting used to.
Other sources of vitamin K-2-rich foods include certain fermented raw cheeses, curd, and sauerkrauts. Again, the K-2–rich versions are not likely found in the U.S. as we do not use same families of spore bacteria that produce K2-7–rich sources.
