Roughly 1 in 4 people living in the UK have low vitamin D levels throughout the year — this figure surges up to 40% in the winter months when UV exposure is at its lowest [1].

These figures are shared throughout Europe, with Northern countries experiencing the highest rates of vitamin D deficiency of all.

Vitamin D deficiency can result in significant side effects over time. Everything from cardiovascular health, bone formation, and mood are affected by low vitamin D levels.

The simple solution is to take vitamin D supplements — which is reported to be one of the most common supplements in Europe, accounting for up to 66% of the European population [2].

However, what’s important to consider is that vitamin D doesn’t work alone. It requires the help of another fat-soluble vitamin — vitamin K — to prevent a series of negative side effects that can result from taking vitamin D on its own.

In this article, we’ll explore the important synergistic relationship between vitamin D and vitamin K, and why it’s important you use a supplement that includes both vitamins together. We’ll also cover the benefits of taking vitamin D and K, and what form of each vitamin is considered the best for supplemental use.

Let’s get straight into it.

Nutritional Synergy: Vitamin D & K

As we’ve already mentioned, vitamin D and vitamin K work closely alongside each other. Studies have shown that combination supplements that include both vitamins have a greater positive impact on health than either of these ingredients on their own.

The interaction between these two vitamins is very complicated, so we’ll start by defining the role of each vitamin on its own. Then we’ll discuss why mixing vitamin D and K together is so important for our health.

The Role of Vitamin D

There are two different forms of vitamin D — vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). The man who first discovered vitamin D — Adolf Windaus — discovered three forms of the vitamin which he named D1, D2, and D3. However, it was later discovered that D1 was simply a combination of D2 and D3 — so the term is no longer used.

While both forms of vitamin D are important, vitamin D3 is considered the better option for supplemental use. It’s the same version of vitamin D that’s produced in the skin when exposed to UV light and has a very high absorption rate in supplemental form.

Vitamin D3 acts more like a hormone than a vitamin. Its main purpose is to regulate the balance of calcium in the bloodstream. When calcium levels are too low, vitamin D makes two changes to the body to increase calcium supply:

  1. It increases the absorption of calcium through the gut
  2. It causes bones to release stored calcium

It’s very important that calcium levels are kept at a constant in the bloodstream. This mineral is a key element of a wide range of important functions in the body.

Calcium is a critical component of the following processes:

  • Blood clotting
  • Nerve transmission
  • Muscle contraction
  • Enzyme activity in the gut, blood, and organs
  • Immune cell activation
  • Energy metabolism

The Problem With Vitamin D

Despite how important this vitamin is for our health, taking too much on its own has been found to lead to a number of negative side effects.

As vitamin D causes calcium levels to increase, a lot of it begins to accumulate in the arteries — which causes the arteries to harden over time. This can lead to high blood pressure and heart disease over time if left unchecked.

This is where vitamin K comes in.

The Role of Vitamin K

Just like vitamin D, there are two different forms of vitamin K. This time researchers got it right the first time — we have vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). Some sources suggest a third type of vitamin K (K3) but this is hotly debated as to whether it actually classifies as vitamin K or not.

Vitamin K1 works exclusively within the liver and has little to do with vitamin D. Vitamin K2 exerts its effects throughout the body — in the bones, the bloodstream, and most organs in the body. This is why K2 is the preferred version for supplemental use — especially in combination with vitamin D.

Vitamin K inhibits the formation of calcium deposits on the arterial walls — which prevents the long-term negative health effects induced by vitamin D supplementation. It does this by changing the chemical structure (carboxylation) of calcium-binding proteins lining the arterial walls.

This effect was proven in a study that induced vitamin K deficiencies in mice, which lead to the formation of calcium plaques on the arterial walls [3]. This effect was further worsened by giving the mice ultra-high concentrations of vitamin D.

Other examples of processes that require both vitamin D and vitamin K to function: 

  • Both vitamins required for blood clotting
  • Vitamin K is required for the reformation of bone after being broken-down by vitamin D
  • Both vitamins work together to regulate blood sugar metabolism
  • Both vitamins work together to regulate several aspects of inflammation and oxidative stress

Evidence-Backed Benefits of Vitamin D3 & K2

1. Healthy Bones

A systematic review found that supplementation of vitamin K reduces bone loss after injuries [6]. Another study found that supplementation of vitamin K reduced the occurrence of new fractures in people with osteoporosis — a condition defined by a low bone mineral density [7]. This effect is especially relevant for men and women experiencing natural age-related bone loss or following a fracture or injury to the bones.

2. Mood & Cognition

Vitamin D has been linked with mood and cognitive symptoms such as depression or an inability to concentrate.

One study found that 58% of Alzheimer’s disease patients had low vitamin D levels (less than 20 ng/mL) [8]. The study concluded that vitamin D deficiencies were associated with low mood and impairment on two of four measures of cognitive performance.

3. Heart Health

The connection between vitamin D, vitamin K, and cardiovascular health is clear — in the majority of studies, people who consume adequate amounts of vitamin D and vitamin K had the lowest incidence of heart disease.

A Czech study found that middle-aged patients with the highest pulse-wave activity (an indicator of arterial rigidity and calcification) had signs of low vitamin K2 (measured by the amount of uncarboxylated MGP) [4].

A different study, published in the Netherlands, found the combination of low vitamin D and low vitamin K were associated with higher blood pressure averages over a 6-year follow-up period [5].


Conclusion: Why You Should Always Take Vitamin D & Vitamin K Together

Vitamin D and vitamin K are both essential for maintaining optimal health — especially when taken together. They each serve separate roles, but evidence suggests these vitamins work better in combination than on their own.

Vitamin D supports calcium balance, which is essential for the function of our neurological, immune, cardiovascular, and digestive systems. Low vitamin D can lead to a deficient immune system, poor concentration, low mood, and much more.

Vitamin K is required for maintaining our bone mineral density and is essential for protecting the cardiovascular system from byproducts manufactured from vitamin D.

Always look for supplements that contain both vitamins for the best results. We prefer to use vitamin D3 due to the higher absorption rate than D2 supplements, and vitamin K2 for its role in protecting the cardiovascular system and building bones.

You can shop our Vitamin D3 & K2 here.


  1. National Diet and Nutrition Survey Results from Years 5 and 6 (Combined) of the Rolling Programme (2012/2013–2013/2014) Public Health England
  2. Van Ballegooijen, A. J., Pilz, S., Tomaschitz, A., Grübler, M. R., & Verheyen, N. (2017). The synergistic interplay between vitamins D and K for bone and cardiovascular health: a narrative review. International journal of endocrinology, 2017.
  3. Price, P. A., Faus, S. A., & Williamson, M. K. (2000). Warfarin-induced artery calcification is accelerated by growth and vitamin D. Arteriosclerosis, thrombosis, and vascular biology, 20(2), 317-327.
  4. Mayer Jr, O., Seidlerová, J., Wohlfahrt, P., Filipovský, J., Cífková, R., Černá, V., … & Jardon, K. M. (2017). Synergistic effect of low K and D vitamin status on arterial stiffness in a general population. The Journal of nutritional biochemistry, 46, 83-89.
  5. Van Ballegooijen, A. J., Cepelis, A., Visser, M., Brouwer, I. A., Van Schoor, N. M., & Beulens, J. W. (2017). Joint association of low vitamin D and vitamin K status with blood pressure and hypertension. Hypertension, 69(6), 1165-1172.
  6. Cockayne, S., Adamson, J., Lanham-New, S., Shearer, M. J., Gilbody, S., & Torgerson, D. J. (2006). Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Archives of internal medicine, 166(12), 1256-1261.
  7. Shiraki, M., Shiraki, Y., Aoki, C., & Miura, M. (2000). Vitamin K2 (menatetrenone) effectively prevents fractures and sustains lumbar bone mineral density in osteoporosis. Journal of bone and mineral research, 15(3), 515-521.
  8. Wilkins, C. H., Sheline, Y. I., Roe, C. M., Birge, S. J., & Morris, J. C. (2006). Vitamin D deficiency is associated with low mood and worse cognitive performance in older adults. The American journal of geriatric psychiatry, 14(12), 1032-1040.