Vitamins and supplements get a lot of attention in the bone health world. Once critically important vitamin that often gets overlooked is Vitamin K. Vitamin K is a fat-soluble vitamin that plays a role in making proteins the body needs for blood clotting, the building of bones, and regulating calcium levels in the blood.

It is fat-soluble, meaning it needs fat to help move it into the bloodstream and can be over consumed. Health providers tend to fear recommending fat soluble vitamins because they can cause harm when over consumed BUT being deficient is equally if not more harmful.

In this article, we investigate the heart and bone benefits related to vitamin K, where they can be found, and how much we need.

What is vitamin K and where is it found?

There are two types of vitamin K, vitamin K1, and vitamin K2. Each type can be found in various food sources. (1, 2, 3)

The K1 variety is the most common type of vitamin K consumed in our diet, the scientific name is phylloquinone. Vitamin K1 can be found in avocado, broccoli, brussels sprouts, cabbage, lettuce, soybean, and dark leafy greens e.g. spinach, kale, swiss chard, and dairy.

Vitamin K2 or menaquinones have several subtypes ranging from MK-1 to MK-13. The two most common are MK-4 and MK-7. MK-4 can be found in some animal products e.g. eggs, organ meats, fatty fish, and dairy. While MK-7 can be found in fermented foods e.g. sauerkraut, miso, and natto (Japanese food made of fermented soybeans), it can also be produced by bacteria in the intestines

One of the key differences between the two is vitamin K1 is absorbed by the body more than vitamin K2.  

OHH Tip: Vitamin K is a fat-soluble vitamin, combine vitamin K-rich foods such as leafy green salads with healthy fats such as olive oil or avocado to boost their absorption.

How much vitamin K do we need?

The Adequate Intake recommended for healthy adults is 120 micrograms and 90 micrograms, for males and females respectively. (4)

To put things into perspective, one cup of raw spinach has about 145 micrograms of vitamin K. (5) Vitamin K is not likely to cause adverse health effects in high doses, so no upper limit has been set. (4)However, physicians are taught to fear vitamin K because there is a belief that consuming foods with high levels or supplementation may cause an increased risk of blood clotting. We will discuss the science behind this shortly.

How does vitamin K keep the heart healthy?

Inadequate vitamin K intake may be linked to the calcification of arteries increasing the risk of heart disease. Calcification of arteries is when calcium and other minerals build up in the walls of blood vessels. (6)

Calcification makes the blood vessels stiffer and reduces the area in which blood can flow making the heart work harder to pump blood throughout the body. This can lead to the development of heart and chronic kidney disease. (6,7)

Vascular smooth muscle cells (VSMC) and chondrocytes (cartilage cells) produce matrix GLA protein (MGP) which plays a role in preventing calcification of blood vessels. Vitamin K is an essential ingredient needed to activate MGP. (8)

The process through which MGP reduces calcification is not very clear. However, it has been suggested that once activated by vitamin K it binds tightly to minerals (hydroxyapatite, calcium, phosphate) in the blood, neutralizing them and stopping them from building up in the walls of blood vessels. (9) Pre-existing calcification may also be reduced when MGP binds to these minerals. After doing so, it stimulates a process called phagocytosis and apoptosis which means to eat and self-destruct, respectively. (9)

Additionally, the formation of bone-forming cells called osteoblasts in the VSMCs also contributes to calcification.  Activated MGP reduces the likelihood of vascular smooth muscle cells (VSMC) from transforming into osteoblasts. (9, 10)

In a long-term study, the risk of heart disease was monitored in 4807 Dutch men and women. They tested participants for vitamin K levels at baseline in the year 1990-1993 and in the year 2000. Results showed that low levels of vitamin K2 were associated with increased risk of blood vessel calcification. (11)

One article compared results from various studies, where participants were given a vitamin K supplement (ranging from 45-360micro grams per day) over 4-9 weeks. (6) Results showed that activated MGP levels increased at the end of the trial, with some studies showing a reduction in arterial stiffness and calcification of blood vessels. (6)

In summary, consuming adequate vitamin K2 through either MK-4 or MK-7 will help to put calcium where it belongs, in the bone! It may help prevent heart attack and stroke too.

How does vitamin K keep bones healthy?

In addition to preventing calcification and allowing the body to pump blood to the heart more smoothly, vitamin K plays a role in bone health.

In the body, bone mineralization is a continuous process that allows the old bone to be replaced with new bone, maintaining quality and quantity of bone.

There are numerous proteins involved in maintaining bone health, including osteocalcin and MGP (yes same one as above), that depend on vitamin K to function properly within the body. (12, 13) Vitamin K activates newly formed osteocalcin. Once activated, osteocalcin binds to calcium and transports it from the blood into the bones inducing bone formation. (12)

Therefore, low levels of vitamin K in the body, meaning less osteocalcin can be activated and less bone mass is being made. Ultimately, this can lead to weaker bones and a higher risk of developing fractures.  When vitamin K intake is low, less MGP is activated. Low levels of activated MGP stimulate the formation of osteoclasts, which are cells that break down bones.  (13, 14, 15)

Heart and bone – hand in hand

In a study consisting of 62 healthy individuals with 387 patients on dialysis, they observed the effect of vitamin K on blood vessel calcification and bone fractures. (16) What they found was the proportion of inactivated MGP was significantly higher in the dialysis group compared to the healthy group. This correlated with a higher incidence of calcification and increased risk of bone fractures.

In the study, vitamin D status was also found to be lower in dialysis patients. (16) One article reviewed results from 18 clinical studies that looked at the effect of vitamin K2 supplementation on bone health and heart health. (17)

The summary of evidence shows that vitamin K2 plays an important role in the prevention of bone loss and calcification of blood vessels. In the same article, they also showed that in four studies, bone loss or lower bone mineral density was associated with a higher chance of blood vessel calcification. (17)

Therefore, if the balance between bone breakdown and bone formation is not maintained, then bone health may be compromised, making them weaker.

Other nutrients?

The beauty of nutrients is they rarely work alone. An example of this is the relationship between vitamin D and vitamin K. Vitamin D promotes the production of proteins such as MGP and osteocalcin, which vitamin K activates thus triggering a cascade of events that support heart and bone health. (18)

One study showed the effect of giving 60 healthy post-menopausal women an olive oil oral supplement enriched with vitamin D (50micrograms), vitamin K (0.7mg), and vitamin B6 daily for one year. Results showed bone mineral density had significantly increased at the end of the study compared to the control group that didn’t take the enriched olive oil. (19)

This emphasizes even further why a varied diet that can offer a range of nutrients is important for reaching optimal health.

Drugs can deplete Vitamin K levels

Vitamin K deficiency is difficult to measure in healthy individuals but may not be that common. Vitamin K can be produced as a by-product of gut bacteria, is available in a range of foods such as dark leafy greens, dairy, eggs, and meat, and small amounts are stored in the liver and fatty tissue for later use.  

However, nutritional inadequacy or certain medications such as antibiotics or some anti-clotting medication can decrease the absorption, availability, and/or efficacy of vitamin K which can lead to a deficiency particularly if taken long term. (20, 21, 22)

Warfarin is a blood thinning medication that prevents the formation of blood clots. It is often prescribed to people with heart disease. It works by blocking vitamin K’s ability to create clotting factors. (23) Warfarin, interferes with the vitamin K dependant MGP, ultimately increasing the risk of blood vessel calcification. (20, 24)

In a study on rats, they compared the effect of vitamin K1 to MK4 (the subtype of vitamin K2) on warfarin-induced calcification of blood vessels. Results showed MK-4 suppressed calcification caused by warfarin. (25)

Does vitamin K in foods or supplements increase my risk of blood clots?

Patients are often told to avoid vitamin k in food or in supplement form because their health care team fears an increase in blood clots. This belief stems from the use of coumadin and it’s known mechanism of blocking vitamin K. However this dogma and belief has never been validated in animal or  human research. K2 in particular has been studied in both MK-4 (26) and MK-7 (27) subtypes with no measurable increase in blood clotting tendency. While you should discuss any supplementation with your health care team if you are told to avoid vitamin K and you are not on coumadin (Warfarin) discuss these studies with your providers.

So, what does all this mean for me?

Luckily, you don’t need to worry about the nitty gritty, simply eating a nutrient-rich diet with great sources of vitamin K AND vitamin D, alongside healthy fats for maximum absorption will put you ahead in terms of your health. We recommend for our patients a combination supplement of vitamins D3 and K2 together to optimize both health and bones!

References:

1. https://pubmed.ncbi.nlm.nih.gov/21088475/  
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5998353/
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6413124/
4. https://www.ncbi.nlm.nih.gov/books/NBK222310/
5. https://fdc.nal.usda.gov/fdc-app.html#/food-details/168462/nutrients  
6. https://pubmed.ncbi.nlm.nih.gov/32391368/
7. https://pubmed.ncbi.nlm.nih.gov/22692665/
8. https://pubmed.ncbi.nlm.nih.gov/32564789/
9. https://www.sciencedirect.com/science/article/pii/S0065242320300160  
10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7552614/
11. https://pubmed.ncbi.nlm.nih.gov/15514282/
12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6955144/
13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6549463/
14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6933527/  
15. https://pubmed.ncbi.nlm.nih.gov/16801507/
16. https://pubmed.ncbi.nlm.nih.gov/22692665/
17. https://pubmed.ncbi.nlm.nih.gov/33917175/
18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5613455/
19. https://pubmed.ncbi.nlm.nih.gov/25600484/
20. https://pubmed.ncbi.nlm.nih.gov/9743228
21. https://pubmed.ncbi.nlm.nih.gov/21775389
22. https://pubmed.ncbi.nlm.nih.gov/20354170/
23. https://pubmed.ncbi.nlm.nih.gov/21088475/
24. https://pubmed.ncbi.nlm.nih.gov/26714212/
25. https://pubmed.ncbi.nlm.nih.gov/26714212/
26. https://pubmed.ncbi.nlm.nih.gov/11846334/
27. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8202544/

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