Vitamin D and vitamin K are two essential vitamins that our body needs to maintain health, which means that if we do not get these vitamins in sufficient amounts, our health will be affected. While most people are familiar with vitamin D, as well as vitamins A, B, C, and E, vitamin K is relatively unknown, especially as it appears that its requirements for maintaining its functions are met through diet. However, awareness of vitamin K is growing as research finds that vitamin K along with vitamin D helps maintain bone health. Before going into how vitamin D and vitamin K work together and the health benefits of taking them together, let's take a closer look at vitamin D, vitamin K and what these vitamins do independently.
Vitamin D is a fat-soluble vitamin that is also called "the sunshine vitamin" because our bodies can synthesize it through the exposure of skin to sunlight. People who regularly spend time in the sun can make sufficient amounts of vitamin D so their need for vitamin D from food is reduced. However, limited sun exposure either because of the climate for those living in northern countries, spending more time indoors than outdoors, and the application of sunscreen leads to insufficient synthesis of vitamin D from the sun. Although foods such as fatty fish, eggs, dairy, and fortified foods contain vitamin D, dietary intake of vitamin D is low. It is therefore not surprising that vitamin D deficiency is incredibly prevalent, affecting about1 billion people throughout the world. (1)
The effects of low vitamin D levels are subtle and are often recognized after the damage has been done. The most well-known consequences of vitamin D deficiency include osteoporosis and an increased risk of falling due to fragile bones. However, recent research also points to an association between vitamin D deficiency and risk of diabetes, cardiovascular disease, autoimmune disease, depression, and even cancer. (1,2)
These are some of the roles that Vitamin D plays in the body (2):
In the sequence of vitamins starting from vitamin A and going steadily to vitamin E, it seems that vitamin K was named randomly. This, however, is not the case. Dr. Henrik Dam, a Dutch nutritional scientist, found a fat-soluble nutrient essential for blood clotting and named it vitamin K, for coagulation, which is the German spelling of coagulation. Like vitamin D, vitamin K is also a fat-soluble vitamin. It is found in many green leafy vegetables, meat, dairy foods, eggs, and fermented soybean products. Additionally, vitamin K is also synthesized by bacteria in the colon. (3,4)
The main and most understood function of vitamin K in the body is its role in regulating the blood clotting process or coagulation when required. However, other roles of vitamin K have been identified that include preventing vascular calcification or hardening of the blood vessels that can cause coronary heart disease. (3) Maintaining healthy bones is another important role of vitamin K, with low bone mineral density and increased risk of bone fractures associated with vitamin K deficiency. (5)
To recap, vitamin K plays these important roles in the body:
Looking at the roles the vitamin D and vitamin K play in the body, it stands out that both these vitamins are necessary for bone health. The question is how do they work together?
But first, let us take a step back to learn a little more about these vitamins. Although often assumed to be single nutrients, vitamin D and vitamin K actually include several forms of these nutrients under a single name. Vitamin D2 and vitamin D3 are two different forms of vitamin D, of which, vitamin D3 has been found to be more effective in raising blood vitamin D levels than vitamin D2. (6)
Vitamin K is found as vitamin K1or phylloquinone, and vitamin K2, which includes a collection of molecules called menaquinones that range from MK-4 to MK-13, based on the length of their isoprenoid side chains. Of the different menaquinones, MK-4 and MK-7 are the most common forms identified for human health. (4,7)
These two vitamins, in the form of vitamin D3 and vitamin K2, play important roles to keep your bones and heart-healthy. (8)
Observational studies show that vitamin D3 and vitamin K2 work together to support bone mineralization by making sure that calcium is absorbed and integrated into the bones. This process is carried out in a series of actions in which both these vitamins play vital roles.
While making sure you are getting sufficient amounts of calcium from your diet is the first step to healthy bones, it is equally important to ensure that the calcium you are eating is available for use by the body. This task falls on vitamin D3, which increases the absorption of calcium from the intestines into the bloodstream and makes it available to be deposited in bones. For this step, vitamin K2 activates a protein called osteocalcin in bones which integrates calcium into the bones. Mineralization of bones with calcium, through the combined efforts of vitamin D and K, increases bone density, makes bones strong and reduces risk of fractures. (3,8)
Evidence supporting the health benefits of taking vitamin D3 and K2 continues to grow as a recent study published in 2020 found that insufficient vitamin D and K contributed to low bone mineral density in young women. (9) Furthermore, a meta-analysis of 8 clinical trials on a total of 971 subjects published in the April 2020 issue of the journal 'Food and Function' found increased bone mineral density when vitamin D and vitamin K were taken together. (10)
Vitamin K has an important role in maintaining heart health by reducing build-up of calcium in the arteries that can result in the formation of plaque. Hardened arteries mean the heart has to pump harder to push blood through arteries that are stiff and rigid. This can reduce the supply of blood and oxygen to different parts of the body and increase the risk of heart disease and stroke. This is where making sure you are consuming adequate amounts of vitamin K becomes important. Vitamin K2 activates a protein called matrix GLA that prevents calcium deposits in the blood vessels, soft tissues, and organs such as kidneys. Sufficient vitamin K2 intakes have been shown to reduce calcification of blood vessels, increase elasticity of blood vessels, and lower the risk of heart disease. (3,4,8)
Putting it together
Based on scientific research, there is strong evidence that vitamin D3 and vitamin K2 make a powerful team and work together to ensure that both your heart and bones are healthy. Remember that taking vitamin D3 without vitamin K2 can cause a buildup of calcium in the arteries, which decreases blood flow through narrowed blood vessels and can negatively impact your heart health. But the health benefits of taking both vitamin D3 and K2 together means that calcium will end up being deposited in bones where it is needed the most.
It is, therefore, crucial that you take sufficient amounts of vitamin D3 and K2 together for both your bones and health. Eating a well-balanced diet and spending time in the sun should provide you with enough amounts of these essential nutrients. However, most adults are stuck indoors and have limited intake of these vitamins. As a result, you may want to consider taking supplements of vitamin D3 and vitamin K2 to meet your daily needs for these nutrients.
About the author
Sukhsatej Batra has a Ph. D in Foods and Nutrition with a passion for motivating people to improve their well-being and achieve results through healthy lifestyle changes. Previously, Sukhsatej has worked as a Senior Research and Development Scientist and college professor.