Do Vitamin D Supplements Even Work If They’re Not Combined With This Nutrient?

Some things in life just seem to pair together naturally—peanut butter and jelly, coffee and quiet mornings, you get the gist. Another one of these natural power couples (or at least so you might think): vitamin D and vitamin K.

These two nutrients are each incredibly important for your health in their own right—and if you’ve seen them packaged together in supplements, you’ve probably wondered: Do I really need to take these two vitamins together?

We get it: Checking off all of the nutrients you need can feel complicated—especially when supplements enter stage left. To keep your routine simple and your mind as clear of all the clutter as possible, here’s what you need to know about vitamin D, vitamin K, and whether or not they should be inseparable in your supplement regimen.

Though you’ve probably heard loads about vitamin D and its many benefits by now, vitamin K doesn’t always get its fair share of the spotlight. (Maybe you’ve heard that it’s important for blood-clotting—but that’s probably it.*)

Here’s some background: Both vitamin D and vitamin K are essential fat-soluble vitamins (along with vitamins A and E). We have daily nutritional needs for both. They also both play starring roles in calcium metabolism and cardiovascular health.* Specifically, vitamin D helps the body produce certain proteins found in bones and blood vessel walls that then need vitamin K—particularly vitamin K2—in order to function properly.*

Wondering what this whole vitamin K2 thing is about? Two forms of vitamin K exist in the body. Vitamin K1 (aka phylloquinone) and vitamin K2 (aka menaquinone). We primarily get vitamin K1 from green leafy vegetables and transport it to the liver. Meanwhile, K2 can be found in fermented dairy and is also naturally produced by the lactic acid bacteria in our gut. It’s this form—K2—that has been studied for its connection to bone and cardiovascular health, among other things.*

Now, about vitamin K2 and its buddy vitamin D3: Current scientific understanding suggests that the two fat-soluble vitamins do, in fact, work together in the body to promote bone formation and support blood vessel wall health and function.*

If you’re wondering what this all means for your supplement routine, right now, well, the answer is not much.

“Some companies offer vitamin D3 and vitamin K2 combination supplements, and that’s fine,” says mbg director of scientific affairs Ashley Jordan Ferira, Ph.D., R.D.N. “They are simply two of the four fat-soluble vitamins our body needs, though, and the direct combination of them in supplements has nothing to do with their absorption; that’s a misconception.” (Vitamin D is required for calcium absorption, hence why you’ll almost always find some necessary vitamin D in calcium supplements.)*

In many cases, fat-soluble vitamins are combined together in supplements for convenience, according to Ferira, who says that supplement complexes containing all four fat-soluble vitamins are also found in the market, including in a high-quality, comprehensive multivitamin.

Ultimately, though, pairing vitamin D and vitamin K2 together in a supplement doesn’t impact the absorption or bioavailability of either, Ferira says, urging that “there is no science to back such a proposition.”

When it does really make sense to see vitamin D (specifically vitamin D3, which is the body’s preferred form) and vitamin K2 together in one supplement? If it’s specifically formulated to support bone or heart health, says Ferira, “like a bone- or heart-health targeted complex.” After all, both nutrients contribute to these areas of your health in significant ways.*

While there’s no harm in supplementing with vitamin D3 and vitamin K2 together, doing so certainly isn’t necessary and doesn’t impact your absorption of either nutrient. However, since both promote cardiovascular and bone health, you might find them (potentially amongst other ingredients) in a complete multivitamin or targeted multi-nutrient formulas created to support your bones and cardiovascular system.*

To support absorption, we designed our vitamin D3 potency+ to include a trio of organic, virgin oils—because vitamin D needs fats, not vitamin K, to be optimally absorbed in the body. “Vitamin K2 has nothing to do with achieving vitamin D sufficiency, which is what this [vitamin D3 potency+] supplement is designed to do,”* Ferira concludes. And there you have it, folks.