What Are the Benefits of D3 and K2? Everything You Need to Know About This Calcium Combo

When we talk about vitamins, we typically use only their main letter—vitamin A, C, D, for example. But there are various forms of each vitamin, and vitamins D3 and K2 are important ones to know because of their benefits for bone health, cardiovascular health, hormonal health, and more. 

As we age, our bone health can naturally decline. After menopause, approximately one in two women—yup, half of us—will break a bone due to osteoporosis. And fractures can be severely disabling, even life-threatening, especially as you get older. 

If you aren’t already paying attention to your bone health, now’s the time to start. The earlier you support your bone health, the better. 

Plus, falling estrogen levels during the menopausal transition along with other midlife health changes increase the risk of cardiovascular disease.

As a result, some experts have started to recommend supplementing with vitamins D3 and K2, both of which play a supportive role in heart health, for women in perimenopause and menopause. So, what exactly are vitamins D3 and K2 good for? Let’s dive in. 

How Your Bone Health Changes With Age

Throughout the first few decades of life, estrogen helps to maintain bone strength and density by promoting new bone formation. But after age 50, a decrease in estrogen levels—combined with normal, age-related wear and tear—can lead to osteopenia, the stage before osteoporosis that’s characterized by lower-than-normal bone density. Without treatment, osteopenia may progress to full-on osteoporosis, a disease that causes bones to become weak and increases the risk of fractures. 

A few other factors may put you at higher risk for bone loss and osteoporosis. These include:

• Having a small body frame
• A family history of osteoporosis
• A history of an eating disorder, such as anorexia 
• Lack of calcium and vitamin D in your diet

Understanding Vitamins D3 and K2

What Is Vitamin D3?

Before we get into the benefits of D3, we’ll back up and explain Vitamin D more generally: Vitamin D is a fat-soluble vitamin best known for its role in bone health. It also supports muscle contraction, heart function, and helps reduce inflammation, among other functions.

Vitamin D comes in two main forms:

• D2 (ergocalciferol)
• D3 (cholecalciferol)

You can get small amounts of both forms of D from plant-based sources and animal products like beef liver, egg yolks, certain cheeses, and the flesh of fatty fish like salmon and mackerel. Your skin can also make vitamin D3 from the sunlight. 

Key Benefits of D2 and D3

Vitamin D, in all its forms, offers several important health benefits, including:

• Bone health: It helps the body absorb calcium, supporting strong bones and reducing the risk of osteoporosis and fractures.
• Immune support: It plays a key role in maintaining a healthy immune system and may help reduce the risk of infections.
• Mood and mental health: Low levels of vitamin D have been linked to mood disorders like depression and seasonal affective disorder (SAD).
• Muscle function: Adequate levels help improve muscle strength and function, which is important for balance and fall prevention.
• Inflammation reduction: Vitamin D may help regulate inflammatory responses in the body.
• Heart health: Some studies suggest it may support cardiovascular function, though research is still ongoing.

As you can see, vitamin D provides a wealth of perks—and yet so many of us are at risk for not getting enough. That includes older adults, people who live in areas with limited sun exposure, those who have dark skin, or people who have a health history of medical conditions that limit nutrient absorption (like celiac or Crohn’s disease) or gastric bypass surgery. This is where supplementation can come in (which we’ll cover below). 

What Is Vitamin K2?

Vitamin K is a fat-soluble vitamin. There are two main vitamin K compounds found in food:

• K1 (phylloquinone), found primarily in green leafy vegetables
• K2 (menaquinones), found in animal-based foods like meat, dairy, and eggs, as well as natto, a fermented soybean food.

Key Benefits of K2

Overall, vitamin K is needed for proper blood clotting, as well as bone and cardiovascular health. You may be at risk for deficiency if you have a malabsorption or GI disorder like celiac disease or ulcerative colitis. Here’s what vitamin K can do for you:

• Bone health: It supports bone mineralization by helping regulate calcium use in the body, reducing the risk of fractures and osteoporosis. In fact, research suggests that K2 supplementation, in particular, may have a positive effect on bone mineral density and may reduce the incidence of fractures in postmenopausal women.
• Heart health: Vitamin K, especially K2, helps prevent calcium from building up in the arteries, which may lower the risk of arterial stiffness and heart disease.
• Blood clotting: Vitamin K is essential for making proteins that help blood clot properly, preventing excessive bleeding.
• Cognitive support: Emerging research suggests vitamin K may play a role in brain health, particularly in older adults.

Why Combine D3 and K2?

Let’s first review the function of vitamins D and K, which will help put it all together. Vitamin D, particularly D3, promotes calcium absorption in the gut, ensuring that calcium from food or supplements can enter the bloodstream. Vitamin K2 plays a complementary role by helping direct calcium out of the bloodstream and into the bones, where it's used by bone-forming cells to maintain strength and structure.

If you are taking supplements, vitamins D3 and K2 may be better together. That’s because they work in tandem. In fact, vitamin D3 promotes the production of proteins that need vitamin K2 in order to function, according to a review in the International Journal of Endocrinology. That research concluded that combined supplementation with vitamin D and vitamin K can be more effective in promoting bone and heart health compared to when used alone. 

A quick word about calcium in all this: Some people may be tempted to add a calcium supplement to create a trifecta for bone support, but there is some concern that taking high doses of calcium alone might raise the risk of arterial calcification, which can encourage the development of coronary artery disease, according to research in Atherosclerosis. Vitamin K2 comes in clutch here because it helps prevent calcium from depositing in blood vessels. That said, calcium intake from food and supplements is generally safe as long as it does not exceed the tolerable upper limit of 2,000-2,500mg/d.

Still, more research needs to be done on calcium supplementation, and for bone health, the best recommendation is to only take a calcium supplement if you can’t meet your needs via diet and a supplement is recommended by your healthcare provider. If that’s the case, it’s worth it to talk to your clinician about the value of including D3 and K2 supplements (or foods rich in these nutrients).

Doctor-Recommended D3 & K2 Supplement Brands

At Midi, we see the perks vitamin D and K can have on a woman's longevity. For that reason, we may recommend D3 and K2 (as MK-7, the most bioavailable form).

Vitamin D3

D3 is the most widely recommended form because it is more effective at raising blood levels of vitamin D and has a longer duration of action than D2.

Brands Midi Recommends: 

• Nordic Naturals Vitamin D3
• Thorne Vitamin D-1000 or D-5000
• Pure Encapsulations D3

1000IU of Vitamin D3 daily is usually sufficient to maintain a serum level over 30 ng/dl, but individual needs may vary.

Vitamin K2

K2 helps direct calcium to the bones and teeth, rather than allowing it to build up in soft tissues like the arteries, making this combination especially beneficial for bone health and cardiovascular protection.

Brands Midi Recommends: 

• Thorne K2
• Life Extension Super K

Optimal Dosage and Supplementation of D3 and K2

It’s essential to focus on your diet and lifestyle first before considering a supplement. Overall, adult women should aim for at least 15 mcg (600 IU) of vitamin D and 90 mcg of vitamin K daily.

However, if you are interested in taking a supplement, talk to a healthcare professional, or a Midi clinician, about if it’s worth adding D3 and K2 supplements to your care plan. Factors that affect if you’re a good candidate for supplementation include your diet, lifestyle, medical history, and health conditions. 

Potential Side Effects and Precautions

When it comes to vitamin D, it’s possible to get too much of a good thing. Taking high doses can make your body absorb too much calcium, which can build up in your blood. This might lead to side effects like:

• Nausea
• Vomiting
• Weakness
• Appetite loss
• Excessive thirst
• Kidney stones

At its worst, overdoing it on vitamin D can cause serious complications, including kidney failure. It’s a good idea to check your vitamin D levels with a blood test before starting a supplement. Work with a healthcare provider, like a Midi clinician, to find a dose that’s right for you. 

As for vitamin K, taking too much via food or supplement is unlikely to cause side effects. However, because K plays a role in blood clotting, it can interact with medications. For example, if you’re taking an anticoagulant (a blood thinner), K can essentially cancel out its effects, so doctors encourage patients to keep their intakes of vitamin K consistent when on these medications. 

The Importance of D3 and K2 for Longevity

There is some evidence that taking the two nutrients together may be more beneficial than either alone. Research has shown that when postmenopausal women with decreased bone mass took vitamin K2 and D3 together for more than a year, they improved their bone mineral density and bone quality more than those who took vitamin K or D alone.

Although more research is needed, there is evidence that having low vitamin D and K may jeopardize your overall health. One study found that adults who had both low vitamin D and K levels may be at greater risk of a cardiovascular event. The reason for the association may have to do with how low vitamin D and K could result in calcification (hardening) of blood vessels, while adequate levels keep vessels elastic (so blood can flow freely).

Key Takeaways

• Vitamin D3 is a form of vitamin D made by the body through sun exposure and found in certain foods and supplements. In supplement form, it’s the most widely recommended form because it is more effective at raising blood levels of vitamin D and has a longer duration of action than D2.
• Vitamin K2 is found in animal-based foods, fermented products, and supplements.
• Some providers recommend taking D3 and K2 together for their complementary roles: D3 helps the body absorb calcium, while K2 helps direct that calcium into bones and away from blood vessels. This synergy may support bone strength and help prevent calcium buildup in arteries, though more research is needed.
• D3 and K2 supplements are generally safe, but you should still consult with a healthcare professional before taking them.

Frequently Asked Questions (FAQs)

What are the benefits of taking D3 and K2 together?

Vitamin D3 and K2 complement each other and may enhance the other’s effectiveness in supporting bone metabolism. Vitamin D promotes calcium absorption, while vitamin K2 plays a role in pulling calcium from the blood so it can be used to build and strengthen your bones. It also helps prevent calcium from building up in blood vessels. Together, this duo promotes bone and heart health. 

Can you take Vitamin K2 and D3 everyday?

Yes, but check with a healthcare provider first to make sure that supplementation with these two nutrients is recommended for you. 

Do K2 and D3 help with weight loss?

K2 and D3 are not indicated for weight loss, and there isn’t robust data to suggest that they are meaningful. 

What happens to your body when you start taking vitamin D3?

The first benefit is that vitamin D3 will help improve calcium absorption in your gut, which can be used to keep bones strong. Additionally, vitamin D also promotes muscle function, immunity, and glucose metabolism.  

Who should not take D3 and K2?

If you have a chronic condition or are taking medication, talk to your doctor first to make sure that your current prescriptions or over-the-counter meds don’t interfere with D3 or K2. And remember: If you get adequate amounts of D3 and K2 through your diet (or sun exposure), additional supplementation may be unnecessary.