Vitamin D3 and K2 Dose Explained: IU, Micrograms and UK Guidance

Vitamin D3 and K2 labels can be confusing. One pouch says 4,000 IU, another 100 µg, another 20,000 IU, and K2 comes in 75, 200 or 500 µg. Here is how to read the numbers, what the UK guidance says, and why strength is not the same as "better".

IU and micrograms: the conversion

Vitamin D is labelled in micrograms (µg) and often also in international units (IU). The conversion is simple: 1 µg of vitamin D = 40 IU.

The NRV (nutrient reference value) for vitamin D is 5 µg. Vitamin K2 has no IU; it is always given in µg, and the NRV for vitamin K is 75 µg.

What the UK guidance says

The NHS advises that everyone should consider taking 10 µg (400 IU) of vitamin D a day during autumn and winter, and that some groups should consider it all year round. It also advises that adults should not take more than 100 µg (4,000 IU) a day unless a doctor has advised it, because taking too much over a long period can be harmful.

That is why high-strength products, such as 10,000 IU or 20,000 IU, are not intended for everyone. If you are considering one, speak to your doctor first, and do not exceed the dose on the label.

What vitamin D and K actually do

These are the authorised health claims in Great Britain, word for word:

• Vitamin D contributes to the maintenance of normal bones.
• Vitamin D contributes to the normal function of the immune system.
• Vitamin K contributes to the maintenance of normal bones.

Anything beyond these on a label or website is not an authorised claim.

Why D3 and K2 are often sold together

Both are fat-soluble vitamins and both have an authorised claim for the maintenance of normal bones, so many people prefer to take them in one capsule. K2 is usually given as MK-7 (menaquinone-7). D3 can come from lanolin (sheep's wool, not vegan) or from lichen or algae (vegan), and a good label tells you which.

How to choose a strength

• Start from the guidance, not the biggest number. 10 µg (400 IU) is the NHS daily amount for autumn and winter; up to 100 µg (4,000 IU) is the adult upper level without medical advice.
• Add up everything you take. Multivitamins, fortified foods and other supplements may already contain vitamin D or K.
• Check the source. If you follow a vegan diet, look for vitamin D3 from lichen or algae.
• Take it with food. As fat-soluble vitamins, D3 and K2 are usually taken with a meal.

Our vitamin D3 and K2 range

• Vitamin D3 4000 IU with K2 MK-7 200 µg, D3 from lanolin
• Vitamin D3 5000 IU with K2 MK-7 200 µg, D3 from lanolin
• Plant-based Vitamin D3 10,000 IU with K2 MK-7 200 µg, vegan
• Calcium Complex with D3, K2 MK-7 and magnesium glycinate

Every listing shows the front and back label, so you can check the exact amount per capsule before you order. High-strength products are for use on a doctor's advice only.

Who should check with a doctor first

• Anyone taking warfarin or another anticoagulant. Vitamin K can affect how these medicines work. Do not take K2 without speaking to your doctor.
• Anyone considering more than 100 µg (4,000 IU) of vitamin D a day.
• Kidney conditions, high calcium levels or sarcoidosis.
• Pregnancy, breastfeeding and under 18s. Speak to your GP or pharmacist about the right amount.

Common questions

Is 4,000 IU of vitamin D a lot?

4,000 IU (100 µg) is the highest daily amount the NHS says adults should take without a doctor's advice. It is 2000% of the NRV.

How many µg is 10,000 IU?

10,000 IU is 250 µg. Divide IU by 40 to get micrograms.

Is K2 MK-7 the same as vitamin K?

MK-7 is one form of vitamin K2, which is part of the vitamin K family. On a label it counts towards vitamin K, with an NRV of 75 µg.

Is vitamin D3 vegan?

Only if it comes from lichen or algae. D3 from lanolin comes from sheep's wool and is not vegan.

This article is for general information and is not medical advice. Food supplements should not replace a varied, balanced diet and a healthy lifestyle. Do not exceed the recommended daily dose.

Sources

• NHS. Vitamin D.
• Department of Health and Social Care. Great Britain nutrition and health claims register.