The short answer
A top place in a vitamin D3 + K2 ranking proves only that a product scored well on whatever that specific ranking chose to measure. It does not prove lab-verified content: measured all-trans MK-7 in supplements ranged from 5.5 to 49 µg per pill, and in one product MK-7 was not found at all despite the label claim.5 The label, the form of K2 and the dose per serving are things you can check yourself.
What does a test winner label measure, and what can it not see?
A test winner label measures the criteria that a particular ranking defined, such as price, declared ingredients or ease of use. It cannot see what laboratory analysis reveals: whether the declared vitamin D3 and K2 are actually in the bottle, and in which chemical form. Unless a ranking publishes a lab result for the batch it tested, a first place is not evidence of content accuracy. Such checks are possible: a validated laboratory method measures vitamin D3, MK-4 and MK-7 in the same supplement, with intra-day precision of 1.9% or better and inter-day precision of 3.5% or better.7
That distinction matters because supplement quality studies repeatedly find gaps between label and laboratory result. In one analysis of fat-soluble vitamins, vitamin D3 content in the tested products was basically similar to what the manufacturer declared, in contrast to vitamin K2, whose content was diverse.8 A ranking that only compares labels would miss exactly this difference. The same applies to the form of K2: a label can say K2 without telling you whether it is MK-4 or MK-7,, or how much of the MK-7 is the all-trans form rather than cis isomers.6
Does the dose on a vitamin D label match what is in the bottle?
For vitamin D3, often yes, but not always perfectly. Measured vitamin D3 content in nine supplements in Hungary (five soft gel capsules and four tablets) stayed within a tolerance limit of 20% below to 50% above the label claim.1 That is compliance, but a wide tolerance band still allows real variation between brands.
Other data show why overages exist. Analytically based estimates predict overages above 20% of label levels for several nutrients in 50 to 99% of multivitamin-mineral products reported in NHANES, and overages of 10 to 20% for calcium in most of them.2 These are predictions for multivitamins, not for D3 + K2 drops, but they show that the number on a label and the amount in a product are two different measurements.
Stability plays a role too. After one month of natural daylight exposure, one of four tested soft gel capsule products showed a 14.7% decrease in vitamin D3.1 So even an accurate label can drift if a product is stored badly, which is a variable no ranking controls for.
Why is vitamin K2 (MK-7) harder to get right than vitamin D3?
Because MK-7 is a fragile molecule whose purity profile and isomer composition depend on how it is produced and what it is mixed with. Studies of finished supplements found all-trans MK-7 contents of 5.5 to 49 µg per pill, with cis/trans isomers in some products exceeding the all-trans content by up to 3.7 times.5
A second analysis of oil capsules and hard tablets identified eleven different cis/trans MK-7 isomers, with cis/trans menaquinone-7 at 70.9 to 218.7 µg and cis/trans menaquinone-6 impurities at 5.5 to 16.9 µg per tablet or capsule; the all-trans content was lower than the isomeric form and often lower than the labels declared.6 So a total K2 number on a label does not tell you how much of it is all-trans MK-7.
Formulation and storage matter as well. MK-7 formulations were stability-tested for 12 months at 25 °C and 60% relative humidity, and for 6 months at 40 °C and 75% relative humidity under accelerated conditions; a higher purity profile of the raw material resulted in enhanced stability in formulations.3 In short: D3 content is usually close to label, K2 content is diverse.8
Is MK-7 the same as MK-4?
No, MK-7 and MK-4 are not the same, even though both are vitamin K2. After a single 420 µg dose with breakfast, MK-7 reached its maximal serum level at 6 hours and stayed detectable up to 48 hours, while MK-4 at 420 µg was not detectable in serum at any time point.4
After 7 consecutive days of 60 µg doses, MK-7 increased serum MK-7 levels significantly in all subjects, whereas MK-4 supplementation did not increase serum MK-4 levels.4
| Property | MK-4 | MK-7 |
|---|---|---|
| Single 420 µg dose, serum detection | Not detectable at any time point | Maximal at 6 h, detectable up to 48 h |
| 60 µg daily for 7 days, serum response | No increase in serum MK-4 | Significant increase in all subjects |
Does the carrier oil or the form change absorption?
The studies in this article do not settle which carrier oil or form absorbs best, so a ranking that awards points for a particular oil is making a judgement these lab results do not support. What the analyses do show is that form affects what a lab finds: one study measured MK-7 in both oil capsules and hard tablets and found the all-trans content often lower than declared in both.6
What you can check is whether the label names the oil and the other ingredients. Vitamin D3 and K2 are fat-soluble vitamins, which is why drops are made with an oil base. If a ranking praises one oil over another, look for the study behind that claim before you let it decide for you.
How do you compare doses per drop, per serving and per day?
You convert everything to a daily average, because labels show per-drop, per-serving and per-day numbers interchangeably. A worked example: our D3 + K2 drops deliver 125 µg vitamin D3 (5000 IU) and 120 µg vitamin K2 as MK-7 per 0.25 ml serving, taken once every 3 days. As a calculation, that averages about 42 µg of vitamin D3 and 40 µg of vitamin K2 per day.
For context, EFSA sets an adequate intake of 15 µg of vitamin D per day for adults9 and a tolerable upper intake level of 100 µg per day.10 The averaged 42 µg per day in this calculation sits between those two reference points, and the per-serving 125 µg dose is spread over 3 days rather than taken daily. When you compare products, always check whether a ranking quotes the per-serving number or the daily number, because they can differ by a factor of three here.
A 20 ml bottle contains about 80 servings of 0.25 ml. The drops use MCT oil from coconut as carrier, with mixed tocopherols.
For these two vitamins, Regulation (EU) No 432/2012 authorises the following claims. Vitamin D contributes to the normal function of the immune system. Vitamin D contributes to normal absorption/utilisation of calcium and phosphorus. Vitamin D contributes to the maintenance of normal bones. Vitamin K contributes to normal blood clotting. Vitamin K contributes to the maintenance of normal bones.11
What should you check on the label yourself?
Check four things a ranking rarely shows: whether content is lab-verified, which form of K2 is used, the exact amount per serving and how often you take it. These are all printed or publishable facts, unlike a ranking score, which is a private calculation you cannot reproduce.
| What a ranking claims | What you can verify yourself |
|---|---|
| Score or star rating | Only as good as the ranking's own criteria; check whether the method is published |
| Labelled K2 content | Lab studies found all-trans MK-7 from 5.5 to 49 µg per pill; one product contained none despite the claim5 |
| Vitamin D3 amount | Measured D3 in nine products stayed within 20% below to 50% above label1 |
| Form of K2 | Look for MK-7 named on the label; serum responses to MK-4 and MK-7 differed sharply4 |
| Serving suggestion | Per drop, per 0.25 ml serving and frequency, recalculated to a daily average |
If you want to go deeper into label numbers, read why two supplement labels print different numbers, and for the wider context of the combination, see our article on the synergy of vitamin D3 and K2. Seasonal needs also differ, as covered in how much vitamin D you need in summer versus winter.
Frequently Asked Questions
Does a test winner guarantee the label is accurate?
No. A ranking result is not a certificate of analysis. Laboratory studies found all-trans MK-7 contents of 5.5 to 49 µg per pill in supplements, with one product containing no detectable MK-7 despite its label claim.5 Only a lab report on the specific batch can confirm content.
Why do some K2 products contain less all-trans MK-7 than the label says?
Because total K2 can include cis isomers. Cis/trans isomers in certain supplements exceeded the all-trans MK-7 content by up to 3.7 times, and the all-trans content was often lower than declared.56 Production method, purification and storage all influence the isomer profile.
Is more vitamin D3 per drop always better?
No. EFSA's tolerable upper intake level for adults is 100 µg of vitamin D per day, against an adequate intake of 15 µg per day. What matters is the daily average: 125 µg taken once every 3 days averages about 42 µg a day, as a calculation.
Does vitamin D3 degrade in the bottle?
It can. After one month of natural daylight exposure, one of four tested capsule products showed a 14.7% decrease in vitamin D3.1 Storing supplements cool, dry and closed protects the content.
Is MK-7 the same as MK-4?
No. After a single 420 µg dose with breakfast, MK-7 reached its maximal serum level at 6 hours and was detectable up to 48 hours, while MK-4 at 420 µg was not detectable in serum at any time point.4 Both are vitamin K2, but they behaved differently in this study.
The Bottom Line
A test winner proves that a product won a particular scoring exercise, nothing more. The evidence says vitamin D3 content is usually close to label within a tolerance of 20% below to 50% above,1 while vitamin K2 content in finished products is diverse8 and the active all-trans MK-7 fraction can fall far below the claim.56 So verify what a ranking cannot show: lab-checked content, MK-7 rather than MK-4,4 the exact amount per serving, the dosing frequency and the named ingredients. Those five checks tell you more than any first place.
Sources
- Quantitative Analysis of the Vitamin D3 Content in Dietary Supplements Marketed in Hungary Using High-Performance Liquid Chromatography. Pharmaceuticals (Basel). 2026.
- Dietary Supplement Ingredient Database (DSID) and the Application of Analytically Based Estimates of Ingredient Amount to Intake Calculations. The Journal of Nutrition. 2018.
- Menaquinone 7 Stability of Formulations and Its Relationship with Purity Profile. Molecules. 2019.
- Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutrition Journal. 2012.
- Identification of cis/trans isomers of menaquinone-7 in food as exemplified by dietary supplements. Food Chemistry. 2018.
- Analysis of Menaquinone-7 Content and Impurities in Oil and Non-Oil Dietary Supplements. Molecules. 2018.
- Simultaneous Determination of Vitamins D3 (Calcitriol, Cholecalciferol) and K2 (Menaquinone-4 and Menaquinone-7) in Dietary Supplements by UHPLC. Molecules. 2021.
- Quality Control of the Dietary Supplements Containing Selected Fat-Soluble Vitamins D and K. Nutrients. 2023.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Dietary reference values for vitamin D. EFSA Journal. 2016.
- EFSA Panel on Nutrition, Novel Foods and Food Allergens. Scientific opinion on the tolerable upper intake level for vitamin D. EFSA Journal. 2023.
- Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. Official Journal of the European Union. 2012.
