There is no single “correct” ratio of vitamin D3 to K2, despite what most supplement marketing pages will tell you.
What actually matters is whether your K2 intake is adequate for the D3 dose you’re taking, that both are taken with a fat-containing meal, and that you take them consistently. This guide walks through the evidence-supported dosage range for adults in the UK, why the popular “100 mcg per 1,000 IU” ratio is marketing rather than science, and how to take D3 and K2 so the nutrients actually do their job.
For the full picture of why these two vitamins work better together, see our complete guide to vitamin D3 and K2 benefits. This post focuses specifically on dose, ratio and timing.
Table of Contents
What the Research Actually Says About the D3:K2 Ratio
Here is the honest position, supported by the clinical literature: there is no established universal ratio of vitamin D3 to vitamin K2. No major health authority (NHS, EFSA, NICE, the NIH, or the Endocrine Society) has published a recommended ratio. No peer-reviewed meta-analysis endorses one.
What the research does show is that adequate K2 becomes more important as D3 intake rises. D3 drives calcium absorption from the gut. K2 activates the proteins that direct that calcium into bone and keep it out of artery walls. If D3 intake goes up without adequate K2, you end up with more circulating calcium and not enough activated routing proteins to place it properly.
So the useful question is not “what ratio?” but whether your K2 intake is adequate for the clinical research dose range. The answer turns out to be simpler than the ratio debate suggests.
Where the “100 mcg per 1,000 IU” ratio comes from, and why we don’t use it
If you search for “D3 K2 ratio” you will find the same figure repeated across dozens of supplement brand blogs: 100 mcg of K2 for every 1,000 IU of D3. It sounds authoritative. It is not.
This ratio originated in supplement industry marketing, not clinical research. It is not supported by a randomised controlled trial, a systematic review, or a major public health body. The clinical trials that established K2’s effect on bone and cardiovascular outcomes (such as the three-year MK-7 trial published in Osteoporosis International in 2013) used doses of 180 mcg daily, independent of D3 dose. The ratio framing retrofits a clean-looking number onto research that never used it.
Our position is the same as the NHS and EFSA position: take D3 within the recommended range, and take K2 within the range supported by clinical trials. That is a more honest answer than any ratio.
Standard Daily Dosage: How Much D3 and K2 Most Adults Need
For healthy adults without deficiency, the evidence supports a tight range for both nutrients.
| Nutrient | Standard daily amount | Notes |
|---|---|---|
| Vitamin D3 | 1,000–2,000 IU | NHS baseline is 400 IU Oct–Mar. 1,000–2,000 IU is the range supported by clinical evidence for adults with limited sun exposure. |
| Vitamin K2 (MK-7) | 90–200 mcg | EFSA adequate intake for total vitamin K is 70 mcg. Clinical trials on bone and arterial outcomes have used 90–200 mcg MK-7. |
The NHS recommends 400 IU of vitamin D for everyone in the UK through autumn and winter. That is a floor, not a target. Clinical evidence on bone, muscle and immune outcomes consistently points to 1,000–2,000 IU daily for adults with limited sun exposure, darker skin, or age over 40. A 2017 meta-analysis in the BMJ covering 25 randomised trials found vitamin D supplementation reduced acute respiratory infections, with the strongest effect in people deficient at baseline.
For K2, the clinical trial range is 90–200 mcg of MK-7 daily. The 2013 Osteoporosis International trial used 180 mcg over three years and found reduced age-related bone density decline in postmenopausal women. A 2015 Thrombosis and Haemostasis trial at the same dose found improved arterial stiffness markers over three years.
Individual variation matters
Response to D3 supplementation varies more than most dosage advice admits. Body weight, baseline blood level, skin tone, gut fat absorption, age, and certain medications all shift the dose needed to reach the same blood level. Some people maintain adequate status on 1,000 IU. Others need 2,500 IU to reach the same 25-hydroxyvitamin D concentration.
The only way to know where you sit is a 25-hydroxyvitamin D blood test through your GP. If you are supplementing at the upper end of the range or correcting confirmed deficiency, periodic testing is a sensible step.
When Higher Doses Are Appropriate (And When They’re Not)
The EFSA tolerable upper intake level for vitamin D is 4,000 IU per day for adults. The NHS advises against exceeding this amount without medical supervision. That is not a target. It is a safety ceiling.
There are two distinct situations where higher doses come into play.
Deficiency correction. People with confirmed vitamin D deficiency (typically below 25 nmol/L) are sometimes prescribed short courses at higher doses, often several thousand IU daily, or weekly loading doses, to bring levels up. This is medical territory. It is not a self-supplementation protocol. If you suspect deficiency, the starting point is a blood test and a conversation with your GP, not a higher-dose supplement bought online.
The upper end of the research range. For adults with limited sun exposure, darker skin, reduced skin synthesis with age, or reduced gut fat absorption, the upper end of the clinical research range (2,000 to 4,000 IU) is supported by research on serum 25-hydroxyvitamin D targets. The Endocrine Society’s clinical practice guidelines suggest 1,500–2,000 IU daily as the amount needed to reliably achieve sufficient blood levels. For adults over 65, research points to 800–1,000 IU year-round as the effective range. See our dedicated guide to vitamin D for seniors for the full breakdown.
At the 4,000 IU upper end, K2 intake matters more, not less. This is why formulations at this dose should always include adequate K2.
How to Take D3 and K2: Timing and Food
Both D3 and K2 are fat-soluble vitamins. The single most important rule for absorption is straightforward.
Take them with a meal that contains fat. A 2010 study in the Journal of Bone and Mineral Research (Mulligan & Licata) found vitamin D taken with the largest fat-containing meal of the day raised blood levels by around 50% compared with taking it on an empty stomach. The meal does not need to be high-fat. Eggs, avocado, nuts, olive oil, oily fish, or full-fat yoghurt all provide enough.
This is also why D3K2 supplements delivered in an oil base perform better than dry capsules. MCT oil provides the fat alongside the vitamin, which is particularly useful for people with reduced gut fat absorption, common in older adults and those on certain medications.
Morning, evening, or with the biggest meal?
There is no strong clinical evidence that morning is better than evening, or vice versa. A few brand blogs suggest evening D3 may interfere with melatonin, but the claim is anecdotal and not supported by controlled research.
The one principle that is well supported is consistency. The best time to take D3 and K2 is the time you will actually remember every day. For most people that means pairing it with an established meal: breakfast if you eat eggs or yoghurt, or dinner if that is your largest meal. We’ll cover timing in more detail in an upcoming dedicated post.
Once daily works for MK-7, not MK-4
This is a form issue more than a timing issue, but it matters for how often you dose. MK-7 has a half-life of around 72 hours, so a single daily dose maintains effective blood levels. MK-4, the other common form of vitamin K2, has a half-life of a few hours and requires multiple doses a day to maintain the same blood concentration. Quality D3K2 supplements use MK-7 for this reason.
Stacking D3 and K2 With Other Supplements
D3 and K2 do not exist in a vacuum. A few interactions are worth knowing.
Magnesium. Magnesium is a cofactor in vitamin D metabolism: the enzymes that convert D3 into its active form (calcitriol) require magnesium to function. People with low magnesium status may respond poorly to D3 supplementation regardless of dose. If you are supplementing D3 and not seeing the serum response you expect, magnesium status is worth checking. For more on forms and timing, see our Magnesium Glycinate product page.
Calcium. K2’s entire role is routing calcium into bone rather than artery. This is the reason D3 and K2 are paired in the first place. If you supplement calcium separately, K2 adequacy is not optional.
Iron and zinc. Both compete with other minerals for absorption. If you take an iron or zinc supplement, spacing it a couple of hours away from calcium-containing meals is sensible, though this is a mineral-timing question rather than a D3K2 timing question.
Warfarin and other coumarin anticoagulants. This is the one hard stop. Vitamin K2 interacts with warfarin and can shift INR unpredictably. Do not supplement with K2 if you take warfarin or any coumarin anticoagulant without first speaking to your GP or anticoagulation clinic. Full interaction detail in our vitamin D3 and K2 side effects guide.
Why Your D3 and K2 Form Matters As Much As The Dose
The right dose delivered in the wrong form still underperforms. Three form choices make a measurable difference.
D3, not D2. Vitamin D3 (cholecalciferol) raises and sustains serum vitamin D levels more effectively than D2 (ergocalciferol). A 2012 meta-analysis in the American Journal of Clinical Nutrition confirmed D3 is the more effective supplemental form. If your current supplement uses D2, switching to D3 will produce a larger rise in blood level at the same dose.
MK-7, not MK-4. As covered above, MK-7’s 72-hour half-life makes once-daily dosing effective. MK-4’s short half-life does not.
Oil-based delivery. Fat-soluble vitamins in an oil base absorb more reliably than dry capsules, particularly in people with reduced gut fat absorption. Our Vitamin D3 K2 formulation uses MCT oil as the carrier, which provides fat directly alongside the vitamins independent of meal composition. For a full ingredient breakdown, see our guide to what’s in our D3K2 and why we chose each ingredient.
How to read a D3K2 supplement label
Most D3K2 labels are easy to misread if you don’t know what to look for. Five checks will tell you whether a product is worth buying.
D3 unit: IU or mcg? Both are used on UK and EU labels. 1,000 IU equals 25 mcg. 4,000 IU equals 100 mcg. If the label shows mcg only, do the conversion before comparing doses.
K2 form: MK-7 or MK-4? MK-7 is the form supported by long-term clinical trials and has the 72-hour half-life needed for once-daily dosing. If the label just says “vitamin K2” without specifying the menaquinone form, assume MK-4 or ask the brand.
K2 dose adequacy. The clinical trial range is 90–200 mcg MK-7. If a product delivers high-dose D3 (2,000+ IU) with only 20–45 mcg K2, the K2 side is underdosed relative to the research.
Carrier. Oil-based carriers (MCT, olive, coconut) absorb more reliably than dry powder capsules, especially for older adults or anyone with reduced fat absorption.
Third-party testing. Look for certificates of analysis, allergen declarations, and clear ingredient sourcing. UK-made products under MHRA oversight are held to documented manufacturing standards.
Frequently Asked Questions
What is the correct ratio of vitamin D3 to K2?
There is no clinically established ratio of D3 to K2. The “100 mcg per 1,000 IU” figure widely shared online originated in supplement marketing, not research. What matters is that your K2 intake sits within the clinical trial range of 90–200 mcg MK-7 daily, and that K2 adequacy becomes more important as D3 dose rises.
How much K2 should I take with 1,000 IU of D3?
90–200 mcg of K2 MK-7 daily. This is the range used across clinical trials on bone and cardiovascular outcomes, independent of D3 dose. At lower D3 doses, 90–100 mcg is sufficient for most healthy adults.
How much K2 should I take with 4,000 IU of D3?
100–200 mcg of K2 MK-7 daily remains the clinically supported range. Do not exceed 4,000 IU D3 without GP supervision, as this is the EFSA tolerable upper limit. K2 adequacy matters more at the upper end of the D3 range.
Should I take D3 and K2 at the same time?
Yes. Both are fat-soluble and benefit from the same meal-with-fat absorption conditions. Most D3K2 supplements combine the two in a single capsule for this reason.
Is it better to take D3 and K2 in the morning or evening?
There is no strong evidence favouring one over the other. Consistency and taking them with a fat-containing meal matter far more than time of day. Pick the meal you reliably eat and stick with it.
Can I take too much vitamin K2?
Vitamin K2 has no established tolerable upper limit, and clinical trials at 180–360 mcg daily over two to three years have shown no significant adverse effects. The one exception is for people on warfarin or other coumarin anticoagulants, who should not supplement K2 without medical oversight.
Do I need to take D3 and K2 every day?
Consistent daily supplementation is more effective than intermittent dosing. Both nutrients are used by the body daily, and steady blood levels matter more than individual large doses. Missing an occasional day is not a problem. Missing most days is.
What D3 and K2 dosage is appropriate for adults over 50?
For adults aged 50 to 64, the upper end of the standard range becomes more relevant. 1,500–2,000 IU of D3 with 100–200 mcg K2 MK-7 daily is evidence-supported, reflecting declining skin synthesis and reduced gut fat absorption that begins in this decade. A 25-hydroxyvitamin D blood test through your GP confirms whether your current intake is sufficient.
What D3 and K2 dosage supports bone health?
Clinical trials on bone outcomes have used 800–2,000 IU D3 with 180 mcg K2 MK-7 daily. A 2013 trial in Osteoporosis International found 180 mcg MK-7 over three years reduced age-related bone density decline in postmenopausal women. A pooled analysis in the New England Journal of Medicine found meaningful fracture risk reduction at 800 IU D3 or above in older adults.
References
- Tripkovic L, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition. 2012;95(6):1357–1364.
- Martineau AR, et al. Vitamin D supplementation to prevent acute respiratory tract infections. BMJ. 2017;356:i6583.
- Knapen MHJ, et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International. 2013;24(9):2499–2507.
- Knapen MHJ, et al. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. Thrombosis and Haemostasis. 2015;113(5):1135–1144.
- Mulligan GB, Licata A. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. Journal of Bone and Mineral Research. 2010;25(4):928–930.
- Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism. 2011;96(7):1911–1930.
- Bischoff-Ferrari HA, et al. A pooled analysis of vitamin D dose requirements for fracture prevention. New England Journal of Medicine. 2012;367(1):40–49.
- NHS. Vitamin D. 2023.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the tolerable upper intake level of vitamin D. EFSA Journal. 2012;10(7):2813.
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any supplement, especially if you are pregnant, have a medical condition, or take prescription medication.
