Should you choose plain vitamin D3, or D3 combined with K2? What is K2 MK-7? And is 4000 IU of vitamin D safe to take daily? This guide answers all three — with authorised claims stated correctly and a straight answer on dosage.
For transparency: vitamins D and K both carry authorised UK claims (D contributes to the maintenance of normal bones; K contributes to the maintenance of normal bones). We state those accurately and don't overreach.
What's the difference between D3 and D3+K2?
- Vitamin D3 alone — a single-nutrient supplement, such as our D3 1000 IU. A sensible, straightforward choice for everyday vitamin D support, especially in winter.
- D3 + K2 — combines vitamin D3 with vitamin K2, such as our D3+K2 4000 IU. The two are paired because both contribute to the maintenance of normal bones, making them a complementary bone-focused combination.
We explain the pairing fully in D3+K2 for bone health. Which to choose depends on whether you want straightforward D3 or the bone-focused D3+K2 combination at a higher D3 strength.
What is vitamin K2 MK-7?
Vitamin K2 comes in different forms, denoted by "MK" numbers. MK-7 (menaquinone-7) is a form of K2 valued for being well-absorbed and long-acting in the body compared with some other forms (such as MK-4). When a label says "K2 as MK-7", it's specifying this particular, well-regarded form — which is what our D3+K2 uses. It's a composition quality signal, much like a standardised extract ratio is for a botanical.
Is 4000 IU of vitamin D safe daily?
Let's be precise, because dosage deserves a careful answer. 4000 IU (100 micrograms) per day is recognised as the tolerable upper intake level for adults set by health authorities — that is, the maximum considered safe for long-term daily intake for the general adult population. So 4000 IU sits at that established upper limit, not beyond it. That said:
- For general winter maintenance, much lower amounts (e.g. 400–1000 IU) are often sufficient — more isn't automatically better.
- Higher-strength products like 4000 IU suit people who want a stronger daily dose within the safe ceiling.
- Don't exceed the upper limit without medical advice, and if you take other supplements containing vitamin D, count those too.
- If you have a medical condition or take medication, check with your GP — especially regarding vitamin K2 if you take anticoagulant (blood-thinning) medication, as K2 can interact with it.
The takeaway
D3 alone is the straightforward choice; D3+K2 pairs two bone-supporting vitamins (with K2 as the well-absorbed MK-7 form); and 4000 IU is at the recognised safe upper daily limit for adults — fine within that ceiling, but more isn't better and K2 interacts with blood thinners. For forms and deficiency, see D3 vs D2; for winter, our vitamin D in winter guide.
Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. Do not exceed 4000 IU (100µg) of vitamin D daily without medical advice. If you take blood-thinning medication, speak to your GP before taking vitamin K2. If you are pregnant, breastfeeding, taking medication or managing a medical condition, speak to your GP or pharmacist before starting a new supplement. Signed, Dr. Miron, Founder of Pure Vitamins UK.
