Vitamin D and K2: Should You Take Them Together?

Vitamin D and K2 have become one of the most popular pairings in the supplement world, and you will often see them sold together in a single softgel. The logic sounds simple: vitamin D helps you absorb calcium, and vitamin K2 helps your body put that calcium to work. But is taking vitamin D and K2 together necessary, or just good marketing?

Here is what the evidence says about how these two nutrients interact, how much of each adults need, where the research is solid and where it is still mixed, and who should be careful before adding K2 to their routine.

How Vitamin D and K2 Work Together

To understand the pairing, it helps to look at what each nutrient does on its own.

Vitamin D: getting calcium in

According to the NIH Office of Dietary Supplements, vitamin D promotes calcium absorption in the gut and helps maintain normal blood levels of calcium and phosphate, which supports normal bone mineralization. In other words, vitamin D is largely about bringing calcium into circulation.

Vitamin K: putting calcium to work

Vitamin K acts as a coenzyme that switches on a group of proteins. Some are clotting factors. Others are directly involved in calcium handling: osteocalcin, which is involved in bone mineralization, and matrix Gla protein (MGP), which may help keep calcium from depositing where it does not belong, such as in blood vessel walls and cartilage. Without enough vitamin K, these proteins stay in an inactive form.

So do they need each other?

The NIH vitamin K fact sheet does not describe a direct interaction between vitamin D and vitamin K. What it does note is that many vitamin K trials also gave participants vitamin D and calcium, which makes it hard to separate their effects. The rationale for taking vitamin D and K2 together is that their jobs are complementary: one increases calcium availability and the other activates the proteins that direct it. That is a reasonable nutritional strategy, but it is not proof that vitamin D is unsafe or ineffective without K2.

How Much Vitamin D and K2 Do You Need?

Official intake targets come from the NIH Office of Dietary Supplements. Vitamin K does not have a separate target for K2; the adequate intake covers all forms.

A quick conversion note: 1 mcg of vitamin D equals 40 IU, so a 2,000 IU supplement provides 50 mcg. The NIH considers blood levels of 25-hydroxyvitamin D of 20 ng/mL (50 nmol/L) or higher sufficient for most people. If you are unsure where you stand, a simple blood test through your doctor beats guessing, and it is the best way to decide whether you need a vitamin D supplement at all.

Why MK-7 is the form most people choose

Vitamin K2 comes in several forms called menaquinones. MK-7 is well absorbed and has a longer half-life than vitamin K1 (phylloquinone), which is one reason it is a popular supplement form. The richest food source by far is natto, a traditional Japanese food made from fermented soybeans, at about 850 mcg of MK-7 per 3-ounce serving. For a full comparison of forms, see our guide to vitamin K2 MK-7 vs MK-4.

What the Research on Vitamin K2 Shows

The most frequently cited K2 trial was published in Thrombosis and Haemostasis in 2015. Researchers randomized 244 healthy postmenopausal women to 180 mcg per day of MK-7 or placebo for three years. Compared with placebo, the MK-7 group showed decreases in two measures of arterial stiffness (carotid-femoral pulse wave velocity and stiffness index beta), and inactive matrix Gla protein (dp-ucMGP) fell 50% compared with placebo. The effects were most noticeable in women who started with higher stiffness. Markers of inflammation were not affected.

It was a randomized, double-blind trial, but keep it in context. It tested a branded MK-7 ingredient (MenaQ7) whose maker publicized the results, it was limited to one population, and it measured vessel stiffness rather than long-term health outcomes. The NIH summarizes the broader picture plainly: observational studies link higher menaquinone intake with less arterial calcification, but clinical trial results have been inconclusive, and findings on bone outcomes are mixed as well.

The fair takeaway: vitamin K2 has a clear biological role in calcium-handling proteins, MK-7 lowered inactive MGP by half versus placebo in the trial above, and the outcome data are promising but not settled.

Should You Take Vitamin D and K2 Together?

For most healthy adults, the pairing makes sense in a few situations:

• You already supplement vitamin D and want the full calcium-handling picture covered.
• You rarely eat natto or other fermented foods, so your MK-7 intake is likely low.
• You are focused on healthy aging and bone health and want nutrients that support calcium metabolism.*

Take both with a meal that contains some fat, since vitamins D and K are fat-soluble. Timing beyond that matters far less than taking them consistently.

Where PureBlood fits

PureBlood™ does not contain vitamin D, so it is designed to sit alongside whatever vitamin D you already get from sun, food or a supplement. Each four-capsule serving provides 200 mcg of K2VITAL vitamin K2 as MK-7, which is above the adult adequate intake for vitamin K. It also includes 2,000 mg of Citrus Bergamot and 10,800 FU of Nattiase Nattokinase to support healthy blood flow and circulation.* You can read more about that ingredient in our nattokinase research breakdown.

Frequently Asked Questions

Is it safe to take vitamin D without K2?

For most people taking vitamin D within recommended amounts, yes. The main documented vitamin D risk is excess intake, which the NIH links to abnormally high blood calcium. Staying at or below the 4,000 IU upper limit unless your doctor advises otherwise is the most important safeguard.

How much K2 should I take with vitamin D?

There is no official ratio and no K2-specific target. The adequate intake for all forms of vitamin K is 90 mcg for women and 120 mcg for men, and the three-year trial discussed above used 180 mcg of MK-7 per day. PureBlood provides 200 mcg per serving.

Who should avoid vitamin K2?

People taking warfarin or other anticoagulants should not start K2 without medical supervision. Formulas that also contain nattokinase, like PureBlood, call for extra caution with any blood-thinning medication or upcoming surgery. Talk to your healthcare provider first if you are pregnant or nursing, have a kidney condition, have a soy allergy, or take other prescription medications.

When is the best time to take vitamin D and K2?

With a meal that includes some fat. Morning or evening both work; pick the time you will remember every day.

The Bottom Line

Vitamin D and K2 are a logical pair: vitamin D brings calcium in, and vitamin K activates the proteins that help direct it. The pairing has a sound biological rationale, but the NIH does not describe a direct interaction, and outcome research on K2 is promising yet still mixed. If you already supplement vitamin D, adding MK-7 is a reasonable step, provided you are not on blood thinners. PureBlood™ delivers 200 mcg of MK-7 alongside Citrus Bergamot and Nattiase Nattokinase in one daily serving.

---

Sources: 1. NIH Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals. 2. NIH Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. 3. Knapen MHJ, et al. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women: a double-blind randomised clinical trial. Thromb Haemost. 2015;113(5):1135-1144.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement.