What "best" means for a vitamin D3 and K2 supplement
Four checks, in this order. The D3 dose, the K2 form, whether there is fat to carry them, and how long the ingredient list runs. Nothing on a UK shelf may be sold as more effective than anything else, so a ranking of brands is a ranking of marketing. A specification is comparable; a verdict is not.
The dose range is set at the top by the NHS: no more than 100 micrograms, or 4,000 IU, of vitamin D a day for an adult.[1] At the bottom it is set by the UK's own advice of 10 micrograms — 400 IU — a day.[1][10] Anything between those two numbers is a legitimate product; anything above the top one is a reason to check what else you are taking.
MK-7 or MK-4: the form that changes the serum result
MK-7, on the one small comparison that exists. Ten healthy women aged 20 to 21 were randomised into two groups of five. In the five given a single 420 microgram dose of MK-4, none was detectable in serum at any time point; in the other five, MK-7 peaked at six hours and was still measurable at 48.[6] Seven days of 60 micrograms daily repeated the split.
| Form | What was given | What happened in serum |
|---|---|---|
| MK-4 | 420 µg single dose to 5 of 10 healthy women aged 20–21, then 60 µg daily for 7 days | Not detectable in any subject at any time point; seven days at 60 µg did not raise serum MK-4[6] |
| MK-7 | 420 µg single dose to the other 5, then 60 µg daily for 7 days | Peaked at 6 hours, still detectable at 48 hours; seven days at 60 µg raised serum MK-7 in every subject[6] |
| K1 vs MK-7 | Matched doses in healthy volunteers | Both peaked at 4 hours, but MK-7's much longer half-life accumulated to 7–8 times higher serum levels over prolonged intake and carboxylated osteocalcin more completely[7] |
Sources: Sato et al., Nutrition Journal 2012;11:93; Schurgers et al., Blood 2007;109(8):3279–3283. Both are small studies, and serum vitamin K levels and osteocalcin carboxylation are laboratory markers rather than health outcomes.
That is why UK labels advertise MK-7 and stay quiet about MK-4. Typical supplement strengths run from 100 to 200 micrograms of MK-7. The NHS dietary figure is roughly 1 microgram of vitamin K per kilogram of body weight a day — about 75 micrograms for a 75kg adult.[2]
The two limits and the one rule worth knowing before you buy
First, 4,000 IU of vitamin D is the adult ceiling for the total across everything you take, not per product.[1] Second, the NHS says taking 1mg or less of vitamin K supplements a day is unlikely to cause harm, and that there is not enough evidence about higher doses.[2]
Third, no brand may claim to treat or cure anything. The only wording a UK label may carry is on the Great Britain register. Vitamin D contributes to the normal absorption and utilisation of calcium and phosphorus, to the maintenance of normal bones, teeth and muscle function, and to the normal function of the immune system. Vitamin K contributes to normal blood coagulation and to the maintenance of normal bones.[5] Food supplements are not medicines.[9]
What is the best brand of vitamin D3 and K2 to take?
None of them, as a category — the question that can be answered is which specification to match. A product worth buying states the D3 dose in both micrograms and IU, and names the K2 as menaquinone-7 with a microgram figure. It declares a fat carrier such as olive or MCT oil. Beyond that, the list should run to the carrier, the capsule or gummy base and little else.
Format changes what "short list" can mean. A tablet can be almost nothing but the actives and a binder; a gummy always carries a base of sweetener, pectin, flavouring and a glazing agent, because that is what makes it a gummy. The check is not whether a base exists but whether anything beyond the base and the named actives is doing work — the honest reading of "vitamin D3 and K2 without bulking agents".
Two words on a front label do less than they look. "Organic" is a farming certification, and vitamin D3 and MK-7 in supplements are produced by synthesis or fermentation rather than farmed, so the word describes the other ingredients at most. "Best quality" and "best rated" are marketing, not a defined standard — the quality signals that exist are the microgram figures, the named K2 form and the carrier.
What should you not take with D3 and K2?
Warfarin, first and without qualification. The NHS says not to take vitamin K supplements while you are taking warfarin.[3] A study of MK-7 found that preparations supplying 50 micrograms a day or more may interfere with oral anticoagulant treatment in a clinically relevant way.[7] A typical UK D3+K2 product carries two to four times that.
After that, the risk is arithmetic rather than chemistry. A multivitamin, a cod liver oil capsule and a standalone D3+K2 product together can pass the 4,000 IU adult ceiling without any single label looking unreasonable.[1] Add up what you already take before adding anything.
Is it better to take vitamin D3 and K2 together?
Convenient rather than superior, on the evidence that exists. Both are fat-soluble, so both benefit from the same meal, and a combined product removes one thing to remember. What has not been shown is that the pair works better than the two taken separately — no trial has tested that against the outcome most people care about.
The genuine argument for a combined product is adherence. A single one-a-day attached to a meal is easier to keep up than two bottles, and the trials that moved vitamin D absorption moved it by changing the meal, not the molecule.[8]
What happens if you take vitamin D3 and K2 every day?
Within the limits, nothing dramatic — that is the point of a daily nutrient. Vitamin D taken consistently maintains the blood level the UK's 10 microgram advice is designed to support.[10] MK-7 accumulates: in the Schurgers comparison, its much longer half-life built serum levels 7 to 8 times higher over prolonged intake than the matched K1 dose reached.[7]
Above the limits the answer changes. The NHS warns that more than 100 micrograms of vitamin D a day could be harmful for an adult.[1] It also says there is not enough evidence to know the effects of high daily doses of vitamin K supplements.[2]
Is it better to take D3 and K2 at night or morning?
Neither, and no trial has compared the two for blood vitamin D status. The variable with evidence behind it is the meal: a fat-containing meal raised the 12-hour plasma vitamin D3 peak by 32% against a fat-free one, 95% CI 11% to 52%, in 50 adults.[8]
The NHS instruction for colecalciferol names a meal rather than an hour — take it with your main meal of the day.[4] Whichever meal is the most reliable in your week is the right one to attach it to.
Which brand of vitamin D3 and K2 is best?
The choice that actually changes anything is format, not brand. Vitamin D3 is sold in the UK as tablets, capsules, chewable tablets, dissolvable tablets, oral drops, oral solution and gummies, and the NHS gives a different instruction for each of the licensed medicine formats.[4]
| Format | How it is taken | What it changes for a D3 and K2 product |
|---|---|---|
| Tablets and capsules | Swallowed whole with water, with the main meal of the day[4] | The shortest possible ingredient list; a softgel can carry the oil itself |
| Chewable tablets | Chewed, not swallowed whole[4] | No water needed; still wants the meal for the fat |
| Dissolvable tablets | Dropped into a glass of water and drunk as soon as they dissolve[4] | Useful if swallowing is difficult; carries a base to make it dissolve |
| Oral drops | Dropped straight into the mouth or onto a spoon[4] | Usually oil-based, so the fat carrier is built in |
| Oral solution | Measured with the syringe supplied[4] | Easiest format to dose down for a child |
| Gummies | Chewed; not a licensed medicine format, so the NHS gives no instruction | Always carries a base — sweetener, pectin, flavouring, glazing agent |
Format instructions are the NHS's, for colecalciferol as a licensed medicine.[4] A food supplement in the same format is taken the same way.
Then compare two labels rather than two names. Put the D3 microgram figure, the MK-7 microgram figure, the carrier and the servings per pack side by side, and divide the price by the servings for a cost per day. Everything else on the front of a UK pack is design.
What to avoid when taking vitamin D3 and K2?
Four things, all avoidable. Taking it on an empty stomach forgoes the fat-meal advantage described above.[8] Stacking products pushes the daily vitamin D total past 4,000 IU without any single label looking wrong.[1]
Third, do not assume a product marked "vitamin K" is K2 — leafy greens and many multivitamins supply K1, which behaves differently in the blood.[2][7] Fourth, do not start one at all while taking warfarin without speaking to your doctor first.[3]
What is the best D3 and K2 supplement in the UK?
UK regulation makes that question unanswerable on purpose. Every food supplement sold here works from the same Great Britain register of authorised claims, so no product may be presented as more effective than another, and none may claim to treat a deficiency.[5][9]
What UK rules do guarantee is disclosure. The label must state the amount of each nutrient per serving. Any two products can therefore be compared on D3 micrograms, MK-7 micrograms, carrier and cost per day, which is the whole of the answerable question.
- Four checks decide it: D3 dose, K2 as MK-7, a fat carrier, and a short ingredient list.
- A single 420 µg dose of MK-4 was undetectable in serum in every subject; the same dose of MK-7 peaked at 6 hours and lasted 48.
- MK-7 accumulated to 7–8 times higher serum levels than K1 over prolonged intake.
- The adult ceiling is 100 µg (4,000 IU) of vitamin D a day across everything you take, not per product.
- The NHS says not to take vitamin K supplements while taking warfarin; 50 µg a day of MK-7 is enough to matter.
Vitgem sells one product in this category, not a ranking of them. Our vitamin D3 4000 IU + K2 200 mcg gummies also carry 600 mg of calcium and sit at the adult daily ceiling for vitamin D.
The MK-7 in them is four times the 50 microgram figure in the anticoagulant finding above. All three are reasons to read the label before you add anything else to it. The rest of our gummy vitamins range lists every amount the same way.
Related reading
Why the two are sold together at all, and what each one is legally allowed to say, is set out in our guide to vitamin D3 + K2 benefits.
References
- NHS. Vitamin D — Vitamins and minerals. link
- NHS. Vitamin K — Vitamins and minerals. Reviewed 2020. link
- NHS. Warfarin. link
- NHS. Colecalciferol: How and when to take it. Reviewed 2023. link
- Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. GOV.UK. link
- Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutrition Journal. 2012;11:93. link
- Schurgers LJ, Teunissen KJ, Hamulyák K, Knapen MH, Vik H, Vermeer C. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8):3279–3283. link
- Dawson-Hughes B, Harris SS, Lichtenstein AH, Dolnikowski G, Palermo NJ, Rasmussen H. Dietary fat increases vitamin D-3 absorption. Journal of the Academy of Nutrition and Dietetics. 2015;115(2):225–230. link
- Food Standards Agency. Food supplements. link
- Scientific Advisory Committee on Nutrition. Vitamin D and Health. GOV.UK, 2016. link