Vitamin K2Keeping calcium where it’s needed

Vitamin K2 plays a critical role in directing how calcium is used in the body, and what part of the body it ends up in. Vitamin K is necessary for calcium uptake into our bones. This is very important as we want our bones to be strong and dense.

On the other hand, most other organs and systems work much better when they are flexible, such as our beating heart and our pulsing blood vessels. In these systems calcium can be actively detrimental. It is a component of arterial plaque, also known as hardening of the arteries. This contributes to high blood pressure, and is a risk factor for a heart attack or stroke. Reducing arterial calcification helps maintain the elasticity and integrity of blood vessel walls, supporting overall cardio-vascular health, which is so important for all of us.

After menopause, a woman’s risk of having a heart attack or stroke rises to being similar to that of a man, and the risk of osteoporosis also rises significantly.

Fortunately vitamin K can help with both bone density and cardiovascular health as it activates proteins that help direct calcium away from the arteries, and into the bones.

A study published in February 2025, explored how 180 micrograms of vitamin K2, in the MK-7 form, taken for a year, benefitted vascular health and flexibility in 165 women with low vitamin K levels. These women were at different stages of menopause, and postmenopausal women were a particular focus, because of their increased risk for cardiovascular disease.

This clinical trial lasted one year, which is relatively long for a trial. It was important for this to be of some duration, as removing calcium from arterial plaque and improving the density of bones is a slow, long-term process. 

The study found that MK-7 supplementation not only markedly slowed vascular stiffening in postmenopausal women, but in the worst cases, it also it improved other important health indicators. The women who had the stiffest arteries to start with got the most benefit, with arterial stiffness reduced by 13.3%, and blood pressure lowered by 3%.

When it comes to bones, a population-based study looked at the effects of vitamin K on the size of bones, because bone density test results were ambiguous. They found that bone size increased when women who were low in vitamin K took it as a supplement.

So it seems vitamin K doesn’t just reduce calcium being deposited onto arterial walls, it can also help pull it out from there. And it helps put calcium into bones. It can likely therefore help prevent and treat both atherosclerosis and osteoporosis at the same time.

Which vitamin K should people take?

Vitamin K1 is found in highest quantities in green leafy vegetables. It is known for increasing the tendency to clot, which is good to some degree, but not to excess. Getting this in your diet will give you some, but not too much, unless you are on certain blood-thinners (check with your pharmacist). Vitamin K2 doesn’t increase clotting tendency, which is why it is the preferred form to use as a supplement. 

There are sub-types of vitamin K2. The MK-7 (menaquinone-7) form has a longer half-life and superior bioavailability compared to other forms of vitamin K, so it is currently the preferred form.

Natto, a Japanese fermented soy product, is one of the only dietary sources of vitamin K2, but it has a strong pungent flavour and slimy texture: it is definitely an acquired taste that doesn’t appeal to many. Fortunately the drops and capsules sold as supplements don’t taste like that!

We are gradually learning more about the potent synergy between vitamin K2 and vitamin D3. You will often find them in the same supplement for their synergistic benefit, which is especially relevant to women after menopause.