By Dr. Matt Gianforte, D.C. | Functional Medicine Clinician
Vitamin D3 and K2 show up together on a lot of supplement labels. If you're trying to figure out whether you need them, how much is too much, and how to pick a product, this guide is for you.
I'll start with what each vitamin does, who tends to run low, and how testing and dosing work. Then I'll walk you through the D3 + K2 products we carry and how they differ.
Key takeaways
- Vitamin D helps your gut absorb calcium and supports normal bone mineralization. Vitamin K is needed for proteins involved in blood clotting and bone metabolism.
- The blood test for vitamin D status is serum 25-hydroxyvitamin D, written 25(OH)D.
- For adults, the RDA for vitamin D is 600 IU a day (800 IU over age 70), and the upper limit is 4,000 IU a day. Higher doses should be guided by your clinician.
- Vitamin D3 raises blood levels more, and keeps them up longer, than vitamin D2.
- If you take warfarin (Coumadin), talk with your prescriber before adding any vitamin K.
What Vitamin D3 Does
You see, vitamin D's main job is calcium. It helps your gut absorb calcium and keeps calcium and phosphate in the range your body needs for normal bone mineralization. That's why vitamin D and calcium are so often talked about together when it comes to bone health as we age.
The NIH Office of Dietary Supplements also notes that vitamin D plays a role in immune function, muscle and nerve function, inflammation and glucose metabolism.
Supplements come as D2 or D3. Both raise your blood level, but research shows D3 raises it more and keeps it up longer. That's why most practitioner formulas use D3.
What Vitamin K2 Does
Vitamin K is a family of compounds. K1 (phylloquinone) comes mostly from leafy greens. K2 (menaquinones) comes from bacteria and shows up in fermented foods like natto and in some animal foods.
Your body needs vitamin K to activate proteins for blood clotting and bone metabolism. One of those, osteocalcin, is involved in bone. Another, matrix Gla protein, is being studied because it might help reduce abnormal calcification. Research on vitamin K and heart health is still ongoing, so I won't promise anything there.
MK-7 vs. MK-4
K2 comes in several forms. Supplements with K2 use MK-4 or MK-7, and both are among the best-studied forms. Here's what the NIH fact sheet says about them:
- MK-7 is well absorbed and has a longer half-life than K1, meaning it stays in the body longer. In one trial, postmenopausal women who took 180 mcg a day of MK-7 for 3 years had better bone strength and less loss of height in part of the spine.
- MK-4 was used in the older fracture trials, at very high doses of 15 to 45 mg a day. That's 15,000 to 45,000 mcg, far more than the 45 to 180 mcg in the D3 + K2 products below.
The NIH also notes there's little data comparing how well the different forms are absorbed. So I wouldn't get too hung up on the form. Consistency and the right dose for you matter more.
Who May Need Vitamin D
According to the NIH, these groups are more likely to run low on vitamin D:
- Breastfed infants
- Older adults
- People who get little sun
- People with darker skin
- People with conditions that limit fat absorption, such as Crohn's disease, celiac disease, ulcerative colitis, cystic fibrosis or some liver diseases
- People with obesity or who have had gastric bypass surgery
Sunlight through a window doesn't count, by the way. UVB doesn't pass through glass, so sitting by a sunny window won't make vitamin D.
Testing Your Vitamin D Level
The test is serum 25(OH)D. It's the main marker of vitamin D status because it reflects both what your skin makes and what you take in.
Here's how the Food and Nutrition Board reads the numbers, as summarized by the NIH:
- Below 12 ng/mL: risk of deficiency
- 12 to 20 ng/mL: some people may be at risk of inadequacy
- 20 ng/mL or more: enough for most people
- Above 50 ng/mL: can be associated with adverse effects
Not every expert group agrees on these cutoffs, and you should know that. The Endocrine Society's 2024 guideline suggests against routine 25(OH)D testing in the general population when there's no established reason to test. In plain words: testing makes the most sense when you and your clinician have a reason, like a risk factor, a bone concern or a plan to take a higher dose.
Labs look normal, but normal isn't optimal? Maybe. That's a conversation to have with your clinician, with your own numbers in front of you. My guide to understanding your labs can help you get ready for it.
Dosing Basics
Here are the official numbers for adults from the NIH:
- RDA: 600 IU (15 mcg) a day for ages 19 to 70, and 800 IU (20 mcg) a day over 70
- Upper limit: 4,000 IU (100 mcg) a day for adults
The upper limit is the most you can take each day that's unlikely to cause harm. Some clinicians use higher doses for a period of time when a person's level is low. If that's you, work with your clinician on the dose, how long to take it and when to recheck your blood level.
The Endocrine Society also suggests against taking more than the RDA just to lower disease risk if you're a healthy adult under 75. So more isn't automatically better.
Why the caution? Too much vitamin D can raise blood calcium. The NIH lists nausea, vomiting and kidney stones among the possible effects, and serious toxicity can harm the kidneys and heart.
A few practical points from the NIH fact sheet:
- Fat in the gut helps vitamin D absorb, so taking it with a meal makes sense.
- Some medications interact with vitamin D, including orlistat, statins, steroids and thiazide diuretics. If you take any of these, talk with your clinician about your vitamin D.
Vitamin K and Warfarin
Here's what I need you to know. Vitamin K can have a serious interaction with warfarin (Coumadin) and similar blood thinners. These drugs work against vitamin K.
The NIH says people on warfarin need to keep their vitamin K intake consistent, because sudden changes can increase or decrease the drug's effect. So if you take a blood thinner, don't start, stop or change a K2 supplement without talking to your prescriber first.
For vitamin K, the adequate intake is 120 mcg a day for men and 90 mcg a day for women. No upper limit has been set because vitamin K has a low potential for toxicity, but the warfarin issue still applies.
D3 + K2 Products We Carry
Here's what's in each product, based on the current labels in the NIH Dietary Supplement Label Database. Notice that every one of them is above the 4,000 IU upper limit per capsule. That's why I'd only use them with your clinician's guidance and a plan to recheck your blood level.
XYMOGEN K2-D3 10,000
K2-D3 10,000 has 10,000 IU (250 mcg) of vitamin D3 as cholecalciferol and 45 mcg of vitamin K2 as MK-7 per capsule. The label says 1 capsule daily, preferably at mealtime.
That's 2.5 times the adult upper limit, so this is a short-term, clinician-directed product, not a daily maintenance pick. It comes in 60 capsules or a 120-capsule bottle. The label tells people on blood thinners or other medications to discuss interactions with their healthcare professional.
XYMOGEN K2-D3 Max
K2-D3 Max has 5,000 IU (125 mcg) of vitamin D3 and 180 mcg of vitamin K2 as MK-7 per capsule, taken once daily. The 180 mcg of MK-7 matches the daily amount used in the 3-year bone trial mentioned above.
Premier Research Labs Vitamin D3+K2
Premier Vitamin D3+K2 has 5,000 IU (125 mcg) of vitamin D3 and 180 mcg of vitamin K2 (as menaquinone) per capsule, with 30 capsules per bottle. The label describes the D3 as vegan (listed as Vitashine) and the K2 as coming from fermented natto. It is labeled vegan and gluten free. Take 1 capsule daily, or as your health professional directs.
For more on how vitamin D fits into a bone plan, see my page on bone density support. You can also browse our Immune Support collection.
What to Look For in a D3 + K2 Supplement
- D3 rather than D2, since D3 raises blood levels more
- A dose that matches your lab result and your plan. Under 4,000 IU a day unless your clinician says otherwise
- A clear K2 amount and form on the label
- Full disclosure of amounts, with no hidden blends
- A plan to retest if you take a higher dose
Frequently Asked Questions
How much vitamin D is too much?
For adults, the upper limit is 4,000 IU a day. Higher doses are sometimes used for a period of time, but only with your clinician's guidance and follow-up testing.
Why take K2 with D3?
Vitamin D helps you absorb calcium, and vitamin K activates proteins involved in bone metabolism. Pairing them is common, but research on the combination is still developing, so think of K2 as a reasonable partner, not a guarantee.
Is MK-7 better than MK-4?
MK-7 stays in the body longer than K1, and it's the form in the XYMOGEN products we carry, at microgram doses. MK-4 was studied at much higher milligram doses. The NIH notes there's little data comparing the forms directly.
Should I test my vitamin D level before taking it?
If you plan to take more than the RDA, or you have a risk factor like fat malabsorption or limited sun, testing with your clinician makes sense. The Endocrine Society suggests against routine testing in people with no established reason.
Can I take vitamin K2 if I take warfarin?
Only with your prescriber's guidance. Vitamin K can change how warfarin works, so your intake needs to stay consistent.
Should I take vitamin D with food?
Yes, that's a good habit. Fat in the gut helps vitamin D absorb, and the K2-D3 10,000 label says to take it at mealtime.
Vitamin D is simple to test and simple to take. The hard part is getting the dose right for you. Talk with your clinician, look at your numbers together, and pick a product that fits that plan.
References
- NIH Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. Updated June 27, 2025. Available at: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- NIH Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals. Updated March 29, 2021. Available at: https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
- Demay MB, et al. Vitamin D for the prevention of disease: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2024. Available at: https://pubmed.ncbi.nlm.nih.gov/38828931/
- NIH Office of Dietary Supplements. Dietary Supplement Label Database: K2-D3 10,000, XYMOGEN (label 335487). Available at: https://dsld.od.nih.gov/label/335487
- NIH Office of Dietary Supplements. Dietary Supplement Label Database: K2-D3 Max, XYMOGEN (label 303732). Available at: https://dsld.od.nih.gov/label/303732
- NIH Office of Dietary Supplements. Dietary Supplement Label Database: Premier Vitamin D3+K2, Premier Research Labs (label 270063). Available at: https://dsld.od.nih.gov/label/270063
This article is for education and isn't medical advice. Talk with your own provider about your situation.
These statements have not been evaluated by the Food and Drug Administration. Products and information on this site are not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement.
