What Is ADK Supplement? | A, D3 & K2 Explained

An ADK supplement is a combined formula of vitamins A, D3, and K2, used primarily to support bone health and calcium metabolism.

For the full breakdown, see our best ADK Supplement guide.

ADK isn’t a single vitamin—it’s shorthand for three fat-soluble vitamins taken together, typically pairing vitamin A with D3 and K2 (usually as MK-7). The combination exists because these vitamins are believed to work together in calcium handling, which is why manufacturers market them for bone, heart, and immune support. Since ADK isn’t a standardized formula, doses and forms vary considerably between brands, so knowing what each label means helps you pick a product that matches your needs—or decide whether you need one at all.

What Does ADK Do In The Body?

ADK formulas target calcium metabolism: vitamin D3 helps your intestines absorb calcium, while vitamin K2 activates proteins that direct that calcium into bones and teeth instead of soft tissues like arteries. Vitamin A rounds out the trio, contributing to immune function, cell growth, and bone remodeling. The synergy is the selling point—each vitamin relies on the others to do its job well. Manufacturer copy commonly claims support for bone density, calcium utilization, cardiovascular health, and immune function. Take those as supplement marketing statements rather than approved treatment claims; the FDA hasn’t evaluated ADK for preventing or treating any disease.

How ADK Doses Vary By Brand

Because ADK is a category rather than a fixed recipe, the label is everything. The vitamin D3 dose is the biggest variable: some products deliver 5,000 IU per capsule, while others go to 10,000 IU. Vitamin K2 also varies widely, appearing as MK-4, MK-7, or a blend of both. Here’s how a few common US-market formulations compare:

The differences matter. A “5 vs 10” label on BioTE’s line refers to 5,000 versus 10,000 IU of vitamin D3—a substantial jump. Some products include vitamin K1 alongside K2, while others use only K2. When comparing options, the D3 and K2 forms and amounts deserve the most attention.

How To Take ADK Supplements

Most manufacturers recommend a simple daily routine. DaVinci Labs directs one capsule daily, or as a healthcare practitioner advises. Codeage suggests one capsule per day with 8 ounces of water or your preferred beverage, taken with food unless otherwise directed. EvexiPEL and BioTE similarly frame dosing as practitioner-directed, particularly at the higher 10,000 IU level.

The “as directed by your healthcare practitioner” phrasing isn’t boilerplate—it reflects that these are higher-dose products. A standard multivitamin typically provides 400 to 800 IU of vitamin D3; ADK formulas start at 5,000 IU. Stacking ADK with another vitamin D supplement could push your total intake well beyond the tolerable upper limit, so it’s worth adding up your daily D3 from all sources.DaVinci Labs’ ADK white paper explains the rationale behind the combined formula if you want the science in more depth.

Who Should Be Careful With ADK?

Because every ADK product contains vitamin K2, the biggest caution applies to anyone on warfarin or other vitamin-K–sensitive anticoagulants. Vitamin K directly counteracts how these blood thinners work, so combining them can undermine your medication’s effectiveness. If you’re on a blood thinner, this isn’t a supplement to start on your own.

High vitamin D3 is the second flag. Products with 10,000 IU per capsule are at the upper end of dosing and help explain why so many are sold through practitioner channels rather than general retail. Anyone with kidney issues, sarcoidosis, or a history of calcium kidney stones should discuss vitamin D and K supplementation with a clinician first. Dietary claims also vary—DaVinci’s formula is gluten-free, soy-free, and vegetarian, while Dr. Mercola’s K2 comes from fermented chickpeas rather than soy. Check the specific label; “ADK” tells you nothing about allergens.

Is ADK Worth Taking?

For most healthy adults eating a varied diet, a separate ADK supplement is optional. Vitamin D3 is the piece many people genuinely lack, especially in winter months or for anyone who spends little time outdoors. Vitamins A and K are more commonly adequate through food—A from liver, eggs, and orange vegetables, K2 from fermented foods and some animal products.

If you’re considering ADK for bone, heart, or immune support, the most useful first step is a blood test for vitamin D status. That single result tells you whether you even need a high-dose supplement and what level makes sense. If you already know you want one, the differences between formulas—D3 strength, K2 versus K1 forms, and dietary certifications—are the real deciding factors.