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Best Vitamin D3 and K2 Supplements UK: Buyer's Guide 2026

Reviewed and updated: 23 July 2026 Best vitamin D3 and K2 supplements UK: buyer's guide 2026 The best vitamin D3 and K2 supplements UK buyers should look for use D3 (cholecalciferol) rather than D2, pair it with K2 as MK-7 (the longest-lasting menaquinone), state both doses clearly, and are made to a recognised quality standard. That is the short answer. Let me explain why D3 and MK-7 are the preferred forms, what each vitamin supports, the dose and safe upper limit, and the important blood-thinner interaction to know before you buy. Quick answer (TL;DR) What to look for: D3 (not D2), K2 as MK-7, both amounts clearly labelled, clean GMP-made formula. Who it's for: adults topping up vitamin D, especially over the darker UK months; vitamin D contributes to normal immune function, muscle function and the maintenance of normal bones, and vitamin K contributes to normal blood clotting and the maintenance of normal bones. Key caution: vitamin K can interact with warfarin and similar anticoagulants, so talk to your doctor first. The adult upper limit for vitamin D is 100 micrograms (4,000 IU) per day. Why D3 rather than D2? Vitamin D comes as D2 (ergocalciferol) or D3 (cholecalciferol), and the research favours D3 for raising and maintaining vitamin D status. According to research retrieved by Scholar Gateway, a randomised, double-blind trial in 95 healthy adults aged 18 to 50 given 1,000 IU daily for six months over winter found the D3 group reached a significantly higher serum 25-hydroxyvitamin D level than the D2 group (81 vs 52 nmol/L, p<0.001), with D2 and placebo similar by the end (Houghton et al., 2011, DOI). For a UK audience with limited winter sun, that difference is the main reason I would choose D3. More in vitamin D3 vs D2. Why K2 as MK-7? Vitamin K2 (menaquinone) comes in several forms, and MK-7 is the standout for supplements because it is well absorbed and stays in circulation far longer than other forms. According to research retrieved by Scholar Gateway, MK-7 has a serum half-life of around 72 hours versus roughly 3 hours for vitamin K1, giving a steadier daily level (Cirilli et al., 2022, DOI). That long half-life is why a once-daily MK-7 tablet makes sense. See what is vitamin K2 MK-7. What D3 and K2 support Both are vitamins with authorised function claims at meaningful amounts, and it is worth knowing exactly what they cover. Vitamin D contributes to the normal function of the immune system, to normal muscle function, to the maintenance of normal bones and teeth, to the normal absorption and utilisation of calcium and phosphorus, and to normal blood calcium levels. Vitamin K contributes to normal blood clotting and to the maintenance of normal bones. People often pair them because vitamin D supports calcium absorption while vitamin K supports the normal bone roles above. Dose and the safe upper limit Public-health advice in the UK suggests considering a daily 10 microgram (400 IU) vitamin D supplement in autumn and winter. Higher-strength products like ours provide 4,000 IU (100 micrograms) of D3 for a stronger top-up. Be aware that 100 micrograms per day is the adult tolerable upper intake level for vitamin D set by EFSA and UK guidance, so this is a higher-strength option to take as directed and not to stack on top of other high-dose vitamin D. The K2 amount here is 100 micrograms MK-7. If you are unsure what level suits you, a GP can check your vitamin D status. A few cautions worth knowing This is the most important safety point for a D3 and K2 product: vitamin K plays a role in normal blood clotting, so it can interact with warfarin and other vitamin-K-antagonist anticoagulants. If you take a blood thinner, do not start a K2 supplement without speaking to your doctor. Both D3 and K2 are fat-soluble, so take with a meal containing some fat for absorption. People with high blood calcium, kidney problems, sarcoidosis, or who are pregnant or breastfeeding should seek advice before taking high-strength vitamin D. Do not exceed the 100 microgram per day vitamin D upper limit from all sources combined. Food sources and signs you may be low Vitamin D is found in oily fish, egg yolks and fortified foods, but diet alone rarely covers UK winter needs, which is why supplementation is commonly advised. Vitamin K1 comes from leafy greens, and K2 from fermented foods like natto and some cheeses. Low vitamin D is non-specifically associated with tiredness and aches, but these overlap with many causes; a blood test is the only way to confirm status. The buyer's checklist D3 (cholecalciferol), not D2. K2 as MK-7 for a long, steady half-life. Both doses clearly labelled (e.g. 4,000 IU D3 + 100 mcg MK-7). Suitable for your diet; check vegetarian/vegan and allergens. Made in a GMP-certified facility and tested for purity and heavy metals. Sensible dosing within the 100 mcg per day vitamin D upper limit. Where Pure Vitamins fits Our Vitamin D3 + K2 tablets deliver 4,000 IU (100 mcg) of D3 with 100 mcg of K2 as MK-7 in one easy-to-swallow vegetarian tablet, formulated in the UK, made in a GMP-certified facility and tested for purity and heavy metals at our GMP-certified facility. Explore related guides or the full range on our Pure Vitamins UK home page. View Vitamin D3 + K2 Tablets Frequently asked questions Is D3 better than D2? For raising and maintaining vitamin D status, the evidence favours D3, which is why most quality supplements use it. Why combine D3 with K2? Vitamin D supports calcium absorption while vitamin K2 (MK-7) supports the maintenance of normal bones and normal blood clotting; many people prefer them together. How much vitamin D per day? UK advice suggests 10 mcg in autumn and winter; higher-strength options like 4,000 IU exist, but 100 mcg per day is the adult upper limit, not to be exceeded. Can I take K2 with warfarin? Not without medical advice, as vitamin K can interact with warfarin and similar anticoagulants. Sources: Houghton et al. 2011 and Cirilli et al. 2022, retrieved by Scholar Gateway (DOIs linked). Food supplements should not replace a varied, balanced diet and a healthy lifestyle. This is information, not medical advice. If you take anticoagulants, are pregnant or breastfeeding, have kidney problems or high blood calcium, or manage a medical condition, speak to your GP or pharmacist before starting. Dr. Miron, Founder of Pure Vitamins UK. Related articles Vitamin D3 vs D2: which form to choose What is vitamin K2 MK-7? How much vitamin D3 and K2 should you take? Best vitamins for immunity UK Vitamin D3 + K2 tablets (4,000 IU D3 + MK-7) Can vitamin D3 without K2 actually hurt you?