Vitamin D3 and K2 are often combined because both have recognised nutritional functions relating to the maintenance of normal bones. Vitamin D also contributes to normal calcium absorption, while vitamin K contributes to normal blood clotting.
They are still separate nutrients with different roles. A combined product can be convenient, but this does not mean that everyone who takes vitamin D also needs additional K2. It also does not establish that K2 removes calcium from arteries or prevents heart disease.
The right choice depends on the amount of each vitamin, your diet, other supplements, medicines and individual health circumstances.
What is vitamin D3?
Vitamin D3 is a form of vitamin D also known as cholecalciferol. The body can produce vitamin D when bare skin is exposed to sunlight, but it is also obtained from certain foods and supplements.
According to the Great Britain Nutrition and Health Claims Register, vitamin D contributes to:
- Normal absorption and use of calcium and phosphorus
- Normal blood calcium levels
- The maintenance of normal bones
- The maintenance of normal teeth
- Normal muscle function
- Normal immune-system function
- The process of cell division
These claims may only be used for foods and supplements that provide enough vitamin D to meet the conditions of use. They describe normal nutritional functions rather than the treatment or prevention of a medical condition.
What is the difference between vitamin D2 and D3?
The two main forms of vitamin D used in foods and supplements are:
- Vitamin D2: also called ergocalciferol
- Vitamin D3: also called cholecalciferol
Both forms can increase vitamin D intake. Vitamin D3 is widely used in food supplements and may be derived from lanolin or, in some vegan products, lichen.
Do not assume that every D3 product is suitable for vegans. Check the stated source, capsule shell, carrier oil and complete dietary-suitability information.
What is vitamin K2?
Vitamin K refers to a family of fat-soluble vitamins. Its recognised nutritional functions include contributing to normal blood clotting and the maintenance of normal bones.
The principal forms discussed in relation to food and supplements are:
- Vitamin K1: also called phylloquinone and found mainly in green vegetables
- Vitamin K2: a group of compounds called menaquinones
Common forms of vitamin K2 used in supplements include MK-4 and MK-7. These names describe different menaquinones rather than different vitamins entirely.
MK-7 remains in circulation for longer than MK-4, but this does not prove that it is automatically better for every person or purpose. The amount, complete formula, medicines and individual suitability all matter.
Why are vitamins D3 and K2 combined?
Vitamin D and vitamin K both have authorised nutritional functions relating to normal bones, but their functions are not identical.
Vitamin D contributes to normal calcium absorption and normal blood calcium levels. Vitamin K contributes to the maintenance of normal bones and normal blood clotting. These complementary functions provide a logical reason for manufacturers to include both nutrients in one formula.
A combined supplement can also offer practical advantages:
- One product instead of two
- One serving to remember
- Easier comparison of total vitamin D and K intake
- Fewer separate bottles
- A formula designed around bone-related nutrition
These advantages mainly concern convenience and complementary nutritional functions. They do not establish that a combined D3-and-K2 supplement is superior to vitamin D alone for everyone.
Do you need vitamin K2 with vitamin D3?
No official UK guidance states that everyone taking routine vitamin D must also take vitamin K2.
Most people should be able to obtain sufficient vitamin K from a varied diet. A combined product may be relevant for someone who specifically wants both nutrients, but K2 should not be added automatically without considering medication and individual suitability.
This is particularly important for people taking warfarin because vitamin K can affect how the medicine works.
Does K2 prevent calcium from accumulating in arteries?
Claims that vitamin K2 removes calcium from arteries, cleans blood vessels or prevents arterial calcification go beyond what has been established for food supplements.
Vitamin K-dependent proteins are involved in biological processes relating to calcium, bones and blood clotting. However, this does not prove that taking a K2 supplement prevents heart disease or reverses calcium already present in arteries.
The authorised commercial claims for vitamin K are that it contributes to normal blood clotting and the maintenance of normal bones. A supplement should not be marketed as preventing or treating cardiovascular disease.
What does the NHS recommend for vitamin D?
The NHS vitamin D guidance advises that adults and children over four should consider taking a daily supplement containing 10 micrograms of vitamin D during autumn and winter.
Some people should consider taking 10 micrograms throughout the year, including those who:
- Are rarely outdoors
- Are frail or housebound
- Live in a care home
- Usually cover most of their skin when outside
- Have dark skin, including people with African, African-Caribbean or South Asian backgrounds
Ten micrograms of vitamin D is equivalent to 400 international units, commonly shortened to IU.
This public-health recommendation applies to vitamin D. It is not automatically a recommendation to take additional vitamin K2.
How much vitamin K do adults need?
The NHS vitamin K guidance estimates that adults need approximately one microgram of vitamin K each day for every kilogram of body weight.
| Body weight | Approximate daily vitamin K requirement |
|---|---|
| 60kg | 60 micrograms |
| 70kg | 70 micrograms |
| 80kg | 80 micrograms |
| 90kg | 90 micrograms |
This refers to total vitamin K intake rather than establishing an ideal supplemental amount of MK-4 or MK-7. Most people should be able to obtain enough vitamin K through a varied and balanced diet.
Is there a recommended D3-to-K2 ratio?
There is no officially established universal ratio of vitamin D3 to vitamin K2.
Supplement formulas may combine different amounts, but these ratios are product formulations rather than official requirements. A larger vitamin D amount does not automatically require a proportionally larger K2 amount.
Compare each nutrient separately by checking:
- The vitamin D amount in micrograms and IU
- The vitamin K2 amount in micrograms
- Whether K2 is supplied as MK-4, MK-7 or a combination
- The amount provided by the complete daily serving
- Other supplements or prescribed products containing vitamin D or K
- Medicine warnings and individual suitability
Understanding vitamin D micrograms and IU
Vitamin D labels may use micrograms, international units or both. The conversion is:
One microgram of vitamin D equals 40 IU.
| Vitamin D | International units |
|---|---|
| 5 micrograms | 200 IU |
| 10 micrograms | 400 IU |
| 25 micrograms | 1,000 IU |
| 50 micrograms | 2,000 IU |
| 100 micrograms | 4,000 IU |
| 125 micrograms | 5,000 IU |
Vitamin K is normally shown in micrograms, written as mcg or µg. Do not confuse micrograms with milligrams: one milligram equals 1,000 micrograms.
Is a high-strength D3-and-K2 supplement better?
No. Higher amounts do not guarantee better absorption, stronger bones, improved immunity, faster results or greater safety.
The NHS advises most adults to consider 10 micrograms of vitamin D for routine autumn and winter supplementation. Adults should not take more than 100 micrograms, equivalent to 4,000 IU, each day unless following medical advice.
Some people are prescribed higher amounts to treat a diagnosed deficiency. A prescribed treatment plan may include a high initial amount, blood testing and a lower maintenance amount. This is different from choosing a high-strength retail supplement for routine use.
For example, the page for Vitamin D3 and K2 Liquid Drops 5000IU uses 5,000 IU in the product title. Check the physical label to confirm how this amount relates to the measured serving. If a daily serving provides 5,000 IU, that equals 125 micrograms and exceeds the NHS general adult maximum of 100 micrograms per day. It should not be used as a routine daily amount without appropriate professional advice.
What happens if you take too much vitamin D?
Taking excessive vitamin D over a prolonged period can cause too much calcium to build up in the body. This is known as hypercalcaemia and can weaken bones and damage the kidneys and heart.
Possible symptoms can include:
- Nausea or vomiting
- Reduced appetite
- Excessive thirst
- Frequent urination
- Weakness
- Confusion
- Abdominal discomfort
These symptoms can have several causes and should not be self-diagnosed. Seek medical advice if you think you have taken too much vitamin D or develop concerning symptoms while using a high-strength product.
Can you take D3 and K2 with warfarin?
Do not take a vitamin K supplement while using warfarin unless your prescriber or anticoagulation team has specifically told you to do so.
The current NHS warfarin guidance advises people taking warfarin not to take vitamin K supplements. Vitamin K can alter how warfarin works and affect the stability of INR results.
Vitamin K may appear in:
- Vitamin D3-and-K2 supplements
- Bone-health formulas
- Multivitamins
- Calcium supplements
- Men’s and women’s multivitamins
- Menopause supplements
- Greens powders
People taking warfarin are generally advised to keep the vitamin K content of their diet reasonably consistent rather than suddenly avoiding green vegetables. Do not stop warfarin or make major dietary changes without advice from your anticoagulation team.
Other anticoagulants work differently, but anyone taking an anticoagulant or antiplatelet medicine should check with a pharmacist or prescriber before using a combined D3-and-K2 product.
Who else should seek professional advice?
Speak to a GP, pharmacist or another qualified healthcare professional before using a D3-and-K2 supplement if you:
- Take warfarin or another anticoagulant
- Have kidney disease or a history of kidney stones
- Have high blood calcium
- Have hyperparathyroidism or sarcoidosis
- Have a condition affecting fat absorption
- Have had bariatric or digestive surgery
- Take prescribed vitamin D
- Use a calcium supplement
- Are receiving treatment for osteoporosis
- Are pregnant or breastfeeding and considering a high-strength product
- Are choosing a supplement for a child
Do not replace prescribed vitamin D with a shop-bought D3-and-K2 product unless your healthcare professional confirms that its amount and schedule are appropriate.
Food sources of vitamin D
Vitamin D is naturally present in a relatively limited selection of foods, including:
- Oily fish such as salmon, sardines, herring and mackerel
- Egg yolks
- Red meat
- Liver
- Fortified breakfast cereals
- Some fortified spreads and plant-based drinks
Pregnant women should avoid liver and liver products because of their high vitamin A content.
Diet alone may not reliably provide the UK reference amount throughout autumn and winter, which is why seasonal vitamin D supplementation is advised.
Food sources of vitamin K
Vitamin K1 is found particularly in:
- Spinach
- Kale
- Broccoli
- Cabbage
- Brussels sprouts
- Vegetable oils
- Cereal grains
Smaller amounts are found in meat and dairy products. Vitamin K2 occurs in certain fermented and animal-derived foods, although its amount and form vary.
Green vegetables should not be avoided simply because they contain vitamin K. People taking warfarin should follow the dietary advice given by their anticoagulation team.
When should you take vitamin D3 and K2?
There is no universally established best time of day. The most practical time is one that:
- Matches the product directions
- Can be followed consistently
- Fits around medicine instructions
- Does not duplicate another supplement
- Allows accurate measurement of the complete serving
Vitamin D and vitamin K are fat-soluble vitamins, so many products are intended to be taken alongside food or already contain a carrier oil. Follow the directions for the particular formula rather than assuming that every product should be taken in the same way.
Drops, capsules or tablets?
Vitamin D3-and-K2 supplements are available as capsules, tablets, sprays and liquid drops. No format is automatically better for everybody.
Capsules and tablets provide pre-measured servings, while drops require careful measurement using the supplied dropper. Liquid formulas may also contain MCT oil, olive oil or another carrier.
When comparing formats, check:
- The amount of D3 per complete serving
- The K2 form and amount
- The number of drops, capsules or sprays required
- The carrier oil and additional ingredients
- Storage requirements after opening
- Vegetarian or vegan suitability
Our guide comparing liquid vitamins and capsules explains why a liquid is not automatically better absorbed and why the complete formula matters more than format alone.
You can also compare available formats in the liquid supplement collection.
What should you check before buying D3 and K2?
- Vitamin D amount: convert IU to micrograms and compare it with UK guidance.
- Vitamin K2 form: look for MK-4, MK-7 or a clearly described combination.
- The complete serving: establish how many capsules, drops or sprays provide the stated amounts.
- Other sources: check multivitamins, calcium products, cod-liver oil and prescribed vitamin D.
- Medicine warnings: vitamin K is particularly important for people taking warfarin.
- Dietary suitability: check the D3 source, capsule shell, carrier oil and allergens.
- Directions and storage: follow the exact instructions supplied with the product.
- Seller information: choose an identifiable business providing complete ingredients, amounts, warnings and contact details.
If your main concern is tiredness, remember that vitamin D does not have the same authorised reduction-of-tiredness claim as several B vitamins, vitamin C, iron and magnesium. Our guide to vitamins and minerals associated with tiredness explains that distinction.
Frequently asked questions
Why are vitamin D3 and K2 taken together?
They are combined because both have recognised functions relating to the maintenance of normal bones, while vitamin D also contributes to normal calcium absorption. Combining them can be convenient, but it is not essential for everyone.
Do you need K2 whenever you take vitamin D3?
No. Official UK advice recommends routine vitamin D supplementation during autumn and winter but does not state that everyone taking vitamin D must also take K2.
Is MK-7 better than MK-4?
MK-7 and MK-4 are different forms of vitamin K2. MK-7 remains in circulation for longer, but this alone does not prove that it is the best option for every person or product.
What is the best ratio of D3 to K2?
No universal official ratio has been established. Check the vitamin D and K2 amounts separately rather than relying on a marketing ratio.
Can vitamin D3 and K2 be taken every day?
Some products are designed for daily use, but the correct schedule depends on the amounts supplied. Follow the label, check your total intake and do not exceed 100 micrograms or 4,000 IU of vitamin D daily unless advised by a healthcare professional.
Can you take vitamin K2 with warfarin?
Do not take vitamin K supplements while using warfarin unless your prescriber or anticoagulation team has specifically approved them.
Vitamin D3 and K2: the final answer
Vitamin D3 and K2 are combined because both contribute to the maintenance of normal bones. Vitamin D also contributes to normal calcium absorption, normal blood calcium levels and the maintenance of normal muscles and teeth. Vitamin K contributes to normal blood clotting.
A combined product can be convenient, but it is not automatically better than vitamin D alone. There is no official universal D3-to-K2 ratio, and K2 should not be presented as removing calcium from arteries or preventing heart disease.
Check the vitamin D amount in micrograms and IU, the K2 form, the complete serving, duplicated nutrients and medicine warnings. Follow NHS vitamin D guidance and do not use a K2 supplement while taking warfarin unless your healthcare team has specifically approved it.
To compare related supplement labels and formats, explore the Joints & Bones collection.