Vitamin D3 and vitamin K2 are two nutrients that play an important role in long-term health. While each vitamin has powerful benefits on its own, research suggests they work especially well together, particularly when it comes to calcium metabolism, bone health, and cardiovascular health.
Many people supplement with vitamin D to support immunity or bone health. However, increasing vitamin D isn’t helpful if you’re lacking vitamin K because while vitamin D regulates calcium absorption, vitamin K2 helps guide where that calcium goes in the body- for example, into your bones and teeth rather than calcifying in your arteries.
Understanding how these nutrients work together can help you make smarter decisions about diet and supplementation.
The Role of Vitamin D in Calcium Absorption
Vitamin D is often called the “sunshine vitamin” because our bodies produce it when skin is exposed to sunlight.
One of vitamin D’s most important jobs is helping the body absorb calcium from the digestive tract. Without adequate vitamin D, the body cannot efficiently absorb calcium, even if your diet contains plenty of it.
In addition to calcium absorption, vitamin D supports:
- Immune system function
- Muscle health
- Mood and brain health
- Blood sugar balance
- Inflammation regulation
While Vitamin D plays many important roles in our bodies, the absorption of calcium is especially important to our bone and cardiovascular health, and Vitamins D’s role in calcium absorption is only the first step to making sure calcium is working to our benefit.
Once calcium enters the bloodstream, the body still needs to decide where that calcium should be deposited- either in our bones and teeth (which is good) or in soft tissue, like our arteries (not so good).
The Role of Vitamin K in Calcium Distribution
This is where vitamin K becomes extremely important.
Vitamin K activates proteins that help direct calcium into bones and teeth, where it strengthens the skeletal system. At the same time, vitamin K helps prevent calcium from accumulating in arteries where it could calcify and contribute to atherosclerosis and cardiovascular disease.
Vitamin K2 exerts control over calcium distribution by activating two proteins:
Osteocalcin
Helps bind calcium to bone tissue, improving bone mineralization.
Matrix Gla Protein (MGP)
Helps prevent calcium from depositing in blood vessel walls.
Without enough vitamin K2, calcium may circulate in the bloodstream and potentially accumulate in arteries, contributing to arterial calcification, which is linked to cardiovascular disease.
Research has linked higher vitamin K2 intake with:
- Reduced arterial calcification
- Lower risk of coronary heart disease
- Improved vascular health
This is why many health professionals recommend vitamin D3 and vitamin K2 together- again because vitamin D increases calcium absorption, while vitamin K helps ensure calcium ends up in bones rather than arteries.
Vitamin K1 vs Vitamin K2: What’s the Difference?
Vitamin K actually comes in two primary forms, each with different functions in the body.
Vitamin K1 (Phylloquinone)
Vitamin K1 is the most common form found in the diet and plays a key role in blood clotting.
Good food sources include:
- Kale
- Spinach
- Collard greens
- Broccoli
- Other leafy green vegetables
While vitamin K1 is essential for normal clotting, it does not appear to play as strong a role in calcium metabolism as vitamin K2.
Vitamin K2 (Menaquinone)
Vitamin K2 is the form most closely associated with bone health and cardiovascular health.
It helps activate the proteins that move calcium into bones and help prevent it from building up in arteries.
Two forms of K2 commonly used in supplements include:
MK-4
A shorter-acting form found in some animal foods.
MK-7
A longer-acting form that stays in the bloodstream longer and is commonly used in high-quality supplements.
Vitamin D2 vs Vitamin D3: Which Is Better?
Vitamin D supplements also come in two forms.
Vitamin D2 (Ergocalciferol)
Vitamin D2 is derived from plant sources and is sometimes used in fortified foods or prescription supplements.
While it can raise vitamin D levels, research suggests it may be less effective at maintaining vitamin D levels over time.
Vitamin D3 (Cholecalciferol)
Vitamin D3 is the form your body naturally produces when exposed to sunlight.
It is generally considered the preferred form for supplementation because it raises and maintains vitamin D levels more effectively than D2.
Food Sources of Vitamin D and Vitamin K
Vitamin D Foods
Vitamin D occurs naturally in only a small number of foods, including:
- Fatty fish like salmon, sardines, and mackerel
- Cod liver oil
- Egg yolks
- Fortified dairy or plant milks
Sun exposure can also help the body produce vitamin D. Short periods of midday sunlight may support natural production, though this varies based on season, location, and skin tone.
Vitamin K2 Foods
Vitamin K2 is less common in the modern diet but can be found in:
- Natto (fermented soybeans)
- Grass-fed dairy products
- Egg yolks
- Liver and organ meats
- Certain fermented foods
Because these foods are not commonly eaten in large amounts, some individuals choose to supplement. Full-fat dairy provides more vitamin K2 than low fat or non-fat dairy, but it also contains more saturated fat. For heart health, lower-fat dairy is often a better everyday choice to help avoid excess saturated fat, while a K2 supplement can help fill in the gap.
Vitamin D and K Supplementation
If supplementation is appropriate, many people take vitamin D3 along with vitamin K2 together in the same supplement to support balanced calcium metabolism.
You can view the vitamin D supplement I often recommend here:
When choosing supplements, look for:
- Vitamin D3 (cholecalciferol)
- Vitamin K2 (often MK-7)
High-quality supplements often combine these nutrients to support bone and cardiovascular health. To learn more about how to choose high quality supplements, read this article on dietary supplements.
A Note of Caution
Both vitamin D and vitamin K are fat-soluble vitamins, meaning they are stored in body fat and the liver rather than easily excreted in urine.
Because of this:
- Excessive doses can accumulate over time
- Supplementation should be thoughtful, always check with your healthcare team
- Vitamin D levels can be checked with a blood test- supplementing with 2,000 to 5,000 IU’s is generally safe for most people especially in the winter but a serum vitamin D test is simple and can ensure that you are not oversupplmenting.
- Individuals taking blood-thinning medications should consult their healthcare provider before supplementing vitamin K.
If you take more than 5,000 IU’s of vitamin D per day, I strongly recommend taking have your blood tested every three months. This will ensure you’re not taking too much and will allow you to determine the most appropriate dose for you. Vitamin D levels are considered within normal range from 30 ng/mol – 100 ng/mol; however an optimal range is at least 50 ng/mol – 100 ng/mol.
What This Means For You
Vitamin D and vitamin K work together to support healthy calcium metabolism.
Vitamin D helps your body absorb calcium, while vitamin K2 helps ensure that calcium is directed into bones and teeth rather than arteries or other soft tissues.
Together, these nutrients support:
- Bone strength
- Dental health
- Cardiovascular health
- Healthy aging
A combination of nutrient-dense foods, safe sun exposure, and appropriate supplementation can help support these essential nutrients.
If you’re feeling unsure about how to balance vitamin D, vitamin K, and your overall nutrition, you don’t have to figure it out on your own. At Pure Nutrition and Wellness, I help you cut through the noise and create a plan that’s tailored specifically to your body, your labs, and your goals. Whether you’re looking to support heart health or long-term wellness, personalized guidance can make all the difference. Reach out to schedule a free inquiry call– I’d love to help you build a strategy that truly works for you.