Blog Post

Do You Need to Supplement Vitamin K2 Alongside Vitamin D?

Vitamin D and Vitamin K2 Supplements

Vitamin D is linked with a variety of health benefits. If you spend enough time reading or hearing about it though, you will likely hear people saying things like “Make sure you supplement vitamin K2 with it though.”

This post is aimed at covering the benefits of both of these vitamins, as well as if it is necessary to supplement them together.

Theory Behind Why They Should Be Supplemented Together

Taking vitamin D can improve our absorption of calcium. It also can cause our body to produce more vitamin K2-dependent proteins.

Vitamin K2 is responsible for depositing calcium in the “right places” in the body.

The theory basically goes that if you were to supplement vitamin D without sufficient vitamin K2, you would potentially be depositing more calcium in your arteries or other soft tissue.

This could lead to an increased risk of cardiovascular disease.

That mechanism makes sense, but it is worth discussing this concept in far more detail.

Vitamin D by Itself

Vitamin D3

Vitamin D supplementation by itself has a bunch of benefits. We have a full blog post going through that, which is worth checking out.

The bigger question though is: Does vitamin D supplementation WITHOUT vitamin K supplementation lead to a higher risk of cardiovascular disease?

And that leads to another question – if it did, would that mean that having naturally higher vitamin D levels without supplementation would lead to the same problem?

This section will just unpack the research on that first question.

A large 2023 study with 21,315 participants taking 60,000IU vitamin D per month (the equivalent of 2000IU per day) over a 5-year period found a lower rate of CVD.

That study by itself kind of undermines the argument that it is unsafe to take vitamin D without vitamin K.

A review that was put together prior to that in 2021 covering all the research up until that point found:

  • Vitamin D deficiency was associated with increased cardiovascular disease risk factors.
  • Supplementing vitamin D, on average, had not been found to be linked with increasing or reducing the risk of cardiovascular disease.

While there is no strong evidence indicating it helps cardiovascular disease, it is also a stretch to say it increases the risk.

Vitamin K by Itself and Heart Health

Vitamin K-2 Supplement

Research has consistently found that vitamin K supplementation by itself reduces vascular calcification.

Although it is difficult to measure vitamin K status, sub-clinical deficiencies of vitamin K also appear to be relatively common too.

Based on the mechanisms, it makes sense that vitamin K2 can reduce the risk of cardiovascular disease. Unfortunately, we do not have a lot of data directly studying that though.

The best example of research looking at this was an observational study looking at coronary heart disease over an average of 11 years. This study found higher vitamin K2 intake, but not K1 was associated with reduced risk of coronary heart disease.

If vitamin D by itself is not causing an increase in cardiovascular disease issues, and vitamin K2 by itself has promise for helping, is this less about vitamin D and more about vitamin K2?

Vitamin D and Vitamin K Together for Bone Health

Outside of the cardiovascular disease aspect, there is some synergy between vitamin D and vitamin K for bone health.

Both individually can help with improving bone mineral density (assuming low vitamin D and K status otherwise).

There is a lot of evidence that supplementing both options together further improves increases in bone mineral density.

Data from Grassroots Health has also found that vitamin K reduces the amount of vitamin D that needs to be supplemented to increase blood levels significantly.

Vitamin K and Vitamin D Linkage

Vitamin D and Vitamin K Together for Heart Health

A 3-year randomized controlled trial involving 400IU vitamin D and 600mg calcium per day with or without 500μg vitamin K assessed coronary artery calcium progression.

When looking at people who were >85% adherent with supplementation, they found less progression in those who took vitamin K. This study is often referenced when looking at this topic.

Something that makes this complex though is that high-dose calcium supplementation has been linked with cardiovascular disease risk. Another study looking at vitamin D and calcium together found a 24% increased risk of myocardial infarction.

Two trials directly looking at vitamin D versus vitamin D and K found that when vitamin K was added, there was a reduction in vascular calcification progression and cardiovascular risk factors.

The calcium aspect is relevant. But we are still left with another aspect to consider:

  • Vitamin D supplementation by itself has not been linked with an increased risk of cardiovascular disease.
  • Vitamin K supplementation by itself has been shown to reduce the build-up of calcium in the arteries.

Putting vitamin D and vitamin K together might reduce the risk of cardiovascular disease – but that could be largely unrelated to the vitamin D component.

Vitamin K in Food

Similarly, to how vitamin D supplementation is likely only beneficial if levels are sub-optimal, vitamin K supplementation is likely only beneficial when levels are sub-optimal.

Since research indicates that it is likely a lot of people have sub-clinical vitamin K deficiency, it could be worth looking at increasing dietary intake.

Vitamin K1 is largely found in plant foods, particularly dark leafy greens.

Vitamin K2 is largely found in animal and fermented foods.

The below chart lists foods high in vitamin K.

Vitamin K Content of Different Foods

Quick Note on Warfarin

Anybody who is taking warfarin (medication) likely should seek out individualised advice in relation to this topic.

Typically, keeping vitamin K intake stable and consistent is the goal while on Warfarin.

A lot of the time this advice has been translated to “don’t have too much vitamin K” which has led to people specifically trying to limit their intake of green vegetables.

This is a complicated topic since vitamin K is not exclusively in green vegetables and because we also have research indicating that trying to limit vitamin K intake is probably not the best approach.

Because of that, I think it makes sense to seek out individual advice based on your specific situation.

Summary

Overall, this topic is not clear-cut. More research is needed before strong claims can be made.

I wanted to quickly highlight some flaws in the logic certain people use when claiming you need to supplement vitamin K2 alongside vitamin D.

  • Some people highlight that vitamin D and calcium supplementation alongside insufficient vitamin K2 can cause issues. But that does not necessarily translate to “if you supplement vitamin D, you need to supplement vitamin K2.
  • What happens if you already have a good vitamin K intake? Specifically, if your intake of vitamin K2 through your diet was good, you wouldn’t need to supplement.
  • If supplemental vitamin D in appropriate dosages caused this issue, would naturally having good blood levels of vitamin D not cause these same issues? Theoretically, it would. So if we are so concerned about supplementing these two together, should we also not be concerned about people who naturally already have good levels, but are not supplementing vitamin K2?
  • We see research showing high-dose calcium supplementation leading to an increased risk of cardiovascular disease for the reasons people are concerned about with vitamin D. We do not see these issues with appropriately dosed vitamin D in isolation though. Is this more of a calcium issue and less of a vitamin D issue?

Although I see all of these flaws, it also is clear that at a population level, either supplementing vitamin K2 or increasing dietary intake likely does help. And these benefits likely occur with or without vitamin D.

Vitamin D has benefits. Vitamin K has benefits. Supplementing them together likely is synergistic in many ways, including improving bone mineral density.

Although we do not have enough research to say this conclusively, it appears safe to supplement vitamin D by itself in appropriate dosages. Vitamin K2 supplementation might help reduce the risk of cardiovascular disease, but that risk appears to not have been increased by vitamin D supplementation anyway.

By Aidan Muir

Aidan is a Brisbane based dietitian who prides himself on staying up-to-date with evidence-based approaches to dietetic intervention. He has long been interested in all things nutrition, particularly the effects of different dietary approaches on body composition and sports performance. Due to this passion, he has built up an extensive knowledge base and experience in multiple areas of nutrition and is able to help clients with a variety of conditions. One of Aidan’s main strengths is his ability to adapt plans based on the client's desires. By having such a thorough understanding of optimal nutrition for different situations he is able to develop detailed meal plans and guidance for clients that can contribute to improving the clients overall quality of life and performance. He offers services both in-person and online.