An athletic man with his arms raised, with images and text about vitamin D3 and K2, which improve calcium absorption and promote health.

The Importance of K2 in Vitamin D3 Supplements: Enhancing Calcium Absorption

The world is full of synergistic relationships where two things work together to achieve more than they could alone. Such a synergistic relationship exists between vitamin D3 and vitamin K2.

While vitamin D3 is widely recognized for its role in calcium absorption, it is increasingly being understood that vitamin D3 and K2 work together to enhance calcium absorption by the body.

This article will explore the dynamic relationship between vitamin D3 and vitamin K2, especially how they work as a team to enhance calcium absorption and the implications for overall health. 

Overview of vitamin D3

Vitamin D3 is the form of vitamin D synthesized in the human skin and found in animal sources. It is considered the most effective for raising and maintaining adequate vitamin D levels in the body. 

Vitamin D is a fat-soluble vitamin that the body uses for many functions, including calcium absorption. There are two major forms of vitamin D that are important for humans—vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). While D2 is obtained from plants (like mushrooms), D3 is commonly synthesized in the skin when exposed to ultraviolet B radiation from sunlight.

This unique ability to be produced from sunlight has earned vitamin D3 the nickname “the sunshine vitamin.” Sunlight is the main natural source of vitamin D3. But it can also be obtained from animal foods, such as fatty fish, egg yolks, cold liver oils, and fortified foods (like breakfast cereals, yogurt, and milk).

Vitamin D3 is more effective and potent than D2 in raising vitamin D levels in the body. For this reason, vitamin D3 supplements are commonly recommended for maintaining adequate vitamin D levels. 

Once synthesized or ingested, vitamin D3 is biologically inactive and must undergo hydroxylation reactions in the liver and kidneys to become active forms that the body can use.

Functions of vitamin D3

Vitamin D3 plays multiple essential roles in the body, one of the most well-known being maintaining calcium levels. The nutrient does this in two ways:

In addition to regulating calcium metabolism, vitamin D helps with the following:

Symptoms of vitamin D3 deficiency

Symptoms of vitamin D3 deficiency can include:

  • Bone pain
  • Muscle weakness
  • Increased susceptibility to infections
  • Impaired wound healing.

Chronic vitamin D3 deficiency can result in health conditions like osteomalacia (softening of the bones), osteoporosis (bone loss), rickets in children, cardiovascular diseases, and certain cancers.

A blood test measuring serum 25-hydroxyvitamin D level is the most accurate way to determine whether an individual has vitamin D deficiency. Adequate serum vitamin D levels for optimal bone and overall health are between 20 ng/mL (50 nmol/L) and 50 ng/mL (125 nmol/L).

Levels below 20 ng/mL are low and may weaken your bones and affect your health, while levels above 50 ng/mL are too high and may cause health problems. 

Individuals at greater risk of vitamin D3 deficiency include those with limited sunlight exposure, darker skin, dietary restrictions, medical conditions affecting nutrient absorption, and older adults.

Overview of vitamin K2

Vitamin K2 is the form of vitamin K that contributes to blood clotting and is involved in calcium metabolism and bone health. Vitamin K is widely known as a group of fat-soluble vitamins essential for blood clotting and bone health. 

There are two primary/main forms of vitamin K—K1 (phylloquinone) and K2 (menaquinone). K1 and K2 are essential in blood clotting, but K2 is also crucial to calcium metabolism and bone health.

Unlike K1, which is found in leafy vegetables, K2 is found in animal-based food (such as meat, dairy, and eggs) and fermented food (such as cheese). Vitamin K2 has several forms, but the most studied are MK-4 (the type found in animal products) and MK-7 (the type found in fermented foods).

Functions of vitamin K2

Vitamin K2 supports blood clotting and regulates calcium in the body, contributing to bone and cardiovascular health.

It promotes the deposition of calcium in bones, contributing to bone health. It does this by activating osteocalcin, a protein involved in calcium metabolism. This protein binds calcium ions and facilitates their incorporation into the bone matrix, promoting bone mineralization and strength.

Vitamin K2 prevents the deposition of calcium in arteries and soft tissues, supporting cardiovascular health. The vitamin does this by activating the matrix Gla protein (MGP), a potent calcification inhibitor that also helps maintain arterial elasticity.

That is, vitamin K2 activates MGP, and then MGP inhibits calcification in arteries. Inhibiting arterial calcification helps blood vessels remain elastic, reducing the risk of cardiovascular diseases, including strokes and heart attacks.

While vitamin K2 is more recognized for its role in bone and cardiovascular health, it supports blood clotting (just like vitamin K1). It supports the activation of clotting factors II, VII, IX, and X in the liver. These compounds contribute to the formation of fibrin, which is necessary for blood clot formation.

Symptoms of vitamin K2 deficiency

Symptoms of vitamin K2 deficiency include:

  • Susceptibility to osteoporosis (bone loss)
  • Arterial stiffness
  • Impaired calcium metabolism
  • Heavy bleeding.

A popular test for checking an individual’s vitamin K status is a coagulation test called the Prothrombin Time (PT) test. The test measures how long it takes for a blood sample to clot. Blood (with adequate vitamin K levels) takes 11 to 13.5 seconds to clot. If the blood sample takes longer to clot, the individual may have vitamin K deficiency and require vitamin K supplementation.

Individuals at greater risk of vitamin K2 deficiency include those with poor dietary intake, gut dysbiosis affecting synthesis, and medical conditions affecting vitamin K absorption (such as celiac disease, cystic fibrosis, short bowel syndrome, and ulcerative colitis).

Health benefits of K2 in vitamin D3 supplements

While vitamin D3 and K2 individually play important roles in the body, these two vitamins combine to achieve more than they could individually. For this reason, vitamin D3 supplements often come with vitamin K2, allowing users to enjoy the health benefits of the two vitamins, such as: 

Better bone health

Vitamin D3 and K2 work together to support bone health more effectively. Calcium is required for bone growth, development, and maintenance. Vitamin D enhances calcium absorption from the intestine, helping to raise the amount of calcium available to the body.

Vitamin D3 also promotes osteoblastic activity, which stimulates bone production. The nutrient acts directly on bone-building cells in the bone called osteoblasts to secrete vitamin K-dependent proteins called osteocalcin into the blood.

Osteocalcin is responsible for transporting calcium from the blood into the bones. But to do this, it must be activated by vitamin K2. After osteocalcin is activated by vitamin K, the protein binds with calcium ions in the blood and incorporates them into the bone matrix, increasing bones’ mineral density (BMD) and strength.

Vitamin D3 and K2 working together to support bone health.

Vitamin D improves calcium absorption to make calcium available in the blood. So, adequate levels of vitamin D3 are needed to improve serum calcium levels and stimulate osteoblasts to produce bone-building protein osteocalcin. However, without K2, osteocalcin cannot work (or cannot work effectively) to direct calcium to the bones and mineralize new bone matrix.

Low vitamin D3 and K2 levels impair bone mineralization, making bones brittle and more susceptible to fractures. Conversely, adequate intake of D3 and K2 improves bone density and helps in osteoporosis prevention.

Studies have shown that combining D3 and K2 does better for bone health than either D3 or K2 in isolation

Better heart health

The D3 and K2 vitamin pair also work together to improve cardiovascular health by reducing the amount of free calcium in the bloodstream.

Remember that D3 promotes calcium uptake into the bloodstream, ensuring that there is enough serum calcium for various physiological processes, including bone mineralization.

K2 activates proteins that move calcium from the blood into bones, regulating serum calcium levels. Inadequate K2 affects the delivery of calcium to the bones. Not only does this cause porous bones, but the amount of calcium in the blood increases, causing calcium to accumulate in arteries and soft tissues. The accumulated calcium can become calcified, increasing the risk of coronary heart disease.

In the synergistic relationship of D3 and K2, while D3 ensures calcium absorption, K2 ensures it is directed to where it is needed (the bones) and not deposited where it can cause problems (the arteries). K2 also activates matrix Gla protein (MGP), which inhibits arterial calcification by binding excess calcium in the vascular system.

Image showing vitamin D3 and K2 supplements, essential for heart health.

Different studies have demonstrated how combining D3 and K2 is better for heart health than either D3 or K2 alone. In one study, subjects treated with high-dose vitamin D alone exhibited high levels of arterial calcification, leading to a significant mortality rate. 

The study concluded that vitamin D alone is insufficient to prevent dangerous arterial calcification levels. However, combining D3 with K2 effectively reduces arterial calcification.

You may also like: Vitamin D and Your Heart: Balancing Levels to Prevent Palpitations.

Better immunity

Combining vitamin D3 and K2 benefits immunity more than when either vitamin is taken alone. It’s well-known that vitamin D3 plays a crucial role in modulating immune responses. 

Vitamin D supports the function of various immune cells (including T cells, B cells, and macrophages), which are essential for recognizing and combating pathogens. For example, adequate vitamin D3 levels enhance the ability of B cells to produce antibodies to fight pathogens. 

Vitamin D3 also enhances the production of potent antimicrobial peptides (AMPs), such as cathelicidins and defensins, which help the body fight infections.

While K2 is less studied for its effects on immunity, it is known to have anti-inflammatory properties.

So, when you take D3 and K2 together, D3 helps immune responses and enhances antimicrobial activity, while K2 helps reduce excessive inflammation that can impair immune function.

Vitamin D and K2 work together to boost immunity: D3 boosts immune response and antimicrobial activity, while K2 reduces inflammation.

Different studies have demonstrated how vitamin D and K have better effects on immunity. One study investigated the effects of vitamin D and K on COVID-19 patients by comparing the vitamin’s status against the severity of inflammatory responses in patients (determined by the level of interleukin 6 in their blood).

It found that vitamin D status did not significantly affect inflammatory response in COVID patients, but vitamin K status did. Specifically, high vitamin K levels were associated with higher inflammatory response and vice versa, suggesting that vitamin K deficiency was related to the severity of COVID-19 infection. The study concluded that administering vitamin K in combination with vitamin D can improve clinical outcomes for COVID-19 patients.

Also read: Combining Vitamin D3 and K2: Top Benefits Explained for Optimal Health.

Do vitamin D3 and K2 have side effects?

Vitamin D3 and vitamin K2 are generally safe when taken within recommended dosages. However, like any medication or supplement, there are a few side effects you should be aware of.

Let’s start with vitamin D3!

Since vitamin D3 enhances calcium absorption, too much vitamin D3 can cause hypercalcemia (harmful high calcium levels). This can lead to:

  • Nausea
  • Vomiting
  • Muscle weakness
  • Unusual tiredness
  • Pain
  • Loss of appetite
  • Excessive thirst
  • Dehydration
  • Excessive urination
  • Neuropsychiatric disturbances
  • Kidney stones.

In extreme cases, vitamin D toxicity causes cardiac arrhythmia, renal failure, and even death.

Interestingly, vitamin K2 is tolerated much better. Vitamin K toxicity is rare, and the few cases are connected with other forms of vitamin K, not K2. However, some people who take vitamin K2 in excess may have diarrhea or an upset stomach.

How to choose the right vitamin K2 and D3 supplements

When choosing vitamin K2 and D3 supplements, consider the following:

D3+K2 supplements

WhyNotNatural D3 + K2 supplement with coconut MCT oil and organic peppermint flavor, is better than separate bottles of D3 and K2.

Some supplements combine vitamin D3 and vitamin K2. These D3+K2 supplements are more convenient than separate D3 and K2 supplements. 

D3+K2 supplements simplify your supplement regimen. With D3+K2 supplements, you take just one supplement instead of two separate ones to enjoy the goodness of both vitamin D3 and K2. This is especially important if you take other supplements or medications.

A combined D3+K2 supplement also ensures you get the right balance of the two vitamins for maximum effectiveness. The D3+K2 formulations are designed to provide optimal ratios of the two vitamins. With this, you won’t have to guess how much of each vitamin to take separately.

Also, a combined D3+K2 supplement usually costs less than buying two separate supplements.

The Why Not Natural D3-K2 supplement combines vitamin D3 and vitamin K2 in optimal ratios for maximum effectiveness.


A bottle of WhyNotNaturlal D3-K2 liquid supplement provides faster and better absorption compared to pills, capsules or powdered options.

When choosing vitamin D3 and K2 supplements, consider liquid options over pills, capsules, or powder forms. Liquid supplements can be more beneficial than their pill counterparts because the body absorbs liquid supplements faster and better.

Liquid supplements are pre-dissolved, so your body does not need to break it down before it absorbs it. But the body has to break down pills-based supplements before absorbing the vitamins. Moreover, some of the nutrients are lost in the process of breaking down the pills to release the vitamins for absorption.

The Why Not Natural D3-K2 supplement is available in liquid form. Since no breaking down is required, a higher percentage of the nutrients enter your bloodstream where they are needed.

Also read: The Benefits of Liquid B Complex Over Tablets. A Comprehensive Guide.

Fatty acid or oils

Some vitamin D3 and K2 supplements contain fatty acids and oils to help create a favorable environment for vitamin absorption. Always choose these supplements with absorption-aiding fat.

Remember that vitamin D3 and K2 are fat-soluble vitamins. This means they must be dissolved in fats to be absorbed effectively from the digestive tract into the bloodstream. This is why vitamin D supplementation must always be taken with food. However, when you choose vitamin D3 and K2 supplements that contain fatty acids or oils, you can take them with or without food.

The Why Not Natural D3-K2 supplement ticks this box, as it comes with MCT oil. This coconut-derived oil creates a “fatty” environment for optimal vitamin absorption, boosts energy, supports weight management, and benefits the brain. So, this D3+K2 supplement does more for you than other D3+K2 supplements.

WhyNotNatural's D3-K2 Dietary Supplement with Coconut MCT Oil improves absorption, energy, weight management and brain health.


Potency refers to the concentration of the active ingredients per serving of a supplement. Higher potency supplements have more of the active ingredients per serving, while lower potency supplements have less of the active ingredients per serving.

When choosing D3 and K2 supplements, you should go for higher-potency supplements, as these have more vitamins per serving, ensuring you receive adequate amounts of nutrients to achieve the desired health results. 

On the other hand, lower-potency supplements may not provide enough of the nutrients to help you achieve the desired health results.

Also, higher-potency supplements can be more cost-effective in the long run. This is because they require smaller doses per serving compared to lower-potency supplements, making the supplement last longer.

The Why Not Natural D3-K2 supplement is one of the most potent D3+K2 supplements you’ll find. With 5,000 IU (125 mcg) of D3 and 100 mcg of K2 in one half-dropper liquid serving, this supplement will help you quickly build up vitamin D3 and K2 levels to support your bone health, cardiovascular health, and immune system. 

WhyNotNatural D3-K2 Dietary Supplement with 500IU helps you quickly build up vitamin D3 and K2 levels to support your bone health, cardiovascular health, and immune system.

Purity and quality

Sadly, very few supplements are pure (without unnecessary fillers, additives, or allergens). However, these unnecessary ingredients could interfere with the bioavailability, absorption, or effectiveness of the active nutrients. So, always go for pure supplements.

When considering D3 and K2 supplements, check the ingredients list and avoid those with fillers, additives, or allergens.

This is where Why Not Natural shines. We use an ultra-clean formula, delivering a vitamin D3+K2 supplement that is non-GMO, gluten-free, and without preservatives or unnecessary additives.

Third-party testing and certification

WhyNotNatural D3-K2 is rated #1 for quality on Labdoor.

Third-party testing involves an independent lab assessing the supplement's quality, potency, purity, and safety. The assessment ensures that the supplement meets its manufacturer's claims.

Supplements that undergo third-party testing are more likely to meet high-quality standards and regulatory requirements. So, always choose D3 and K2 supplements from reputable brands with third-party certifications. 

Why Not Natural D3-K2 is rated #1 for quality on Labdoor, which uses FDA-registered laboratories to test supplements for purity and label info accuracy. 

With Labdoor’s certification, you can trust that the Why Not Natural D3-K2 supplement contains the stated ingredients in the specified amounts and is pure, not containing fillers without health benefits, artificial preservatives, and other contaminants.


Below, we address some of the most commonly asked questions about taking vitamin D3 and K2. 

Is taking vitamin D3 alone harmful without K2?

Currently, there is no strong proof that taking vitamin D3 alone without vitamin K2 is harmful. However, the evidence suggests that it may be a concern because we do know that high levels of vitamin D3 and low levels of K2 are associated with vascular calcification and increased risks of heart disease.

Who should avoid taking D3 and K2 supplements?

Individuals who should avoid taking D3 and K2 supplements include those with a history of hypercalcemia, those with kidney disease, and those taking anticoagulant medications.

Since D3 enhances calcium absorption, individuals with a history of hypercalcemia (high calcium levels in the blood) should avoid D3, especially at high doses, as it could exacerbate their condition. 

The kidney converts vitamin D from its inactive form to its active form, which regulates calcium by directing calcium from the blood to bones. So, kidney disease impairs the activation of vitamin D, contributing to elevated blood calcium levels. Lastly, since vitamin K2 contributes to coagulation, individuals taking anticoagulation medications (like warfarin) should avoid K2.

Is it better to take vitamin D3 and K2 in the morning or at night?

Many people find that taking vitamin D3 and K2 in the morning is more convenient. There has also been one study of post-menopausal females that found that vitamin D supplementation decreases sleep quality. Therefore, you may want to take your D3 and K2 supplements in the morning instead of at night.

Do D3 and K2 improve sleep quality?

There is limited direct evidence linking D3 and K2 to sleep. However, some studies have suggested that low vitamin D levels are associated with higher risks of sleep disorders. Thus, addressing the vitamin deficiency via vitamin D3 and K2 supplementation may benefit sleep outcomes.

How long does it take to see the benefits of D3 and K2?

How long it takes to see the benefits of D3 and K2 depends on several factors, such as the condition being treated, initial vitamin status, and lifestyle (consistently taking the supplements as recommended, eating a healthy diet, etc.).

However, it takes a few weeks of supplementation for serum levels of D3 and K2 to rise, while it can take months to see improvement in bone density and strength.

Is it safe to take vitamin K2 and D3 every day?

Yes, it is safe to take vitamin D3 and K2 every day. In fact, to achieve the health benefits of D3 and K2 supplementation, you’ll need to take them every day for several weeks or months. 

What should not be taken with K2 and D3?

When taking D3 and K2, avoid taking calcium and magnesium supplements, as these may interfere with the absorption of the vitamins. You should also avoid steroids and medications like anticonvulsants, glucocorticoids, and weight loss medications, as these alter vitamin D metabolism. Since K2 supports coagulation, you should avoid anticoagulants when taking D3 and K2 supplements.

Can I take D3, K2, and vitamin C together?

There is no known interaction between D3+K2 and vitamin C, so you can take vitamin C when taking a D3 and K2 supplement. However, it is wise to consult your health provider before starting any supplement regime.

Can I take a B complex vitamin with D3 and K2?

There’s no known interaction between B complex vitamins and vitamins D3 and K2. For example, there is no absorption interference because B complex vitamins, being water-soluble vitamins, are absorbed well in the digestive tract, regardless of the presence of fat-soluble vitamins like D3 and K2. So, you can take a B complex vitamin with D3 and K2. However, you should consult your healthcare provider for professional advice.

What should be avoided when taking D3 supplements?

When taking D3 supplements, avoid calcium and magnesium supplements, as well as steroids and medications that affect vitamin D metabolism (such as anticonvulsants, glucocorticoids, and weight loss medications). If you must take any of these, space out their intake from the D3 supplement intake by a few hours.

Does K2 increase the risk of blood clots?

No, vitamin K2 does not increase the risk of blood clots because its role in blood clotting is limited to activating clotting factors (unlike K1, which is primarily involved in blood clotting). K2 simply contributes to maintaining stable clotting levels for wound healing rather than causing blood clots in your arteries and veins.

Can vitamin K2 cause joint pain?

Vitamin K2 does not cause joint pain. Rather, vitamin K2 supports bone health by directing calcium to bones, and maintaining strong bones can indirectly support joint function.

Thus, vitamin K deficiency can be associated with joint problems. True to this, many studies have found that low levels of vitamin K are connected to a prevalence of osteoarthritis, a debilitating joint disease.

Which fruits are rich in vitamin K?

Fruit sources of vitamin K include kiwi, blueberries, grapes, figs, avocado pears, and prunes. While these fruits have some vitamin K, they are not as rich in the vitamin as leafy vegetables, such as Swiss chard, collard greens, spinach, kale, and broccoli. 

However, these plant sources of vitamin K deliver K1. K2 is obtained from animal-based food or fermented food.

Takeaway: Support your health and overall well-being with the perfect pair of vitamin D3 and K2

Vitamin D3 and K2 are fat-soluble vitamins that form a perfect pair in the body, working together to achieve far more than they could individually. Combining D3 and K2 is a scientifically supported approach that enhances calcium absorption, improving bone health, heart health, and immunity.

When aiming to improve bone mass, support cardiovascular health, or enhance overall well-being, choosing a high-quality supplement that combines vitamin D3 and K2 is a valuable step toward achieving your goals.

Why Not Natural is the go-to brand for high-quality supplements that work. We’re committed to producing supplements in the way your body craves—100% natural and easily absorbable.

Our vitamin D3+K2 supplement ticks all the right boxes—it combines D3 and K2, the nutrients are in their most bioavailable forms, it is in liquid form and contains MCT oil to enhance absorption, it does not contain harmful fillers and artificial preservatives, it is highly potent, and it has a third-party seal of quality.

Want to move closer to achieving your optimal health goals? Get the Why Not Natural D3-K2 supplement today!

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