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We recommend this particular combination because the D3-plus-K2 formulation reflects how these nutrients actually function in the body — not as standalone additions, but as partners in calcium metabolism. Thorne's use of MK-4, a well-studied K2 form, is the kind of formulation decision that earns a place on our shelves. This is one of the first supplements we suggest when a patient's blood panel reveals low vitamin D.
About this product
Vitamin D and K2
A precision liquid combining vitamin D3 with vitamin K2 (MK-4) in an MCT oil base — the two fat-soluble vitamins that work as a partnership to direct calcium where it belongs (your bones and teeth) and away from where it does not (your arteries and soft tissue). Drop-dose format for flexible dosing from a single bottle that lasts months.
Vitamin D is the supplement almost everyone in the UK should be taking from October to March, and most practitioners now recommend year-round for anyone not regularly exposing significant skin area to direct sunlight. But vitamin D without vitamin K2 is an incomplete intervention — and potentially a counterproductive one. Vitamin D increases intestinal calcium absorption. That is its primary mechanism for supporting bone health. But once calcium is in your bloodstream, vitamin D has no control over where it goes. Without K2, calcium may deposit in arterial walls, heart valves, and kidney tissue instead of bone matrix. You take vitamin D to strengthen your skeleton and inadvertently contribute to vascular calcification — the very process that stiffens arteries and increases cardiovascular risk. This is not a theoretical concern. It is the reason that vitamin D and K2 are increasingly recommended together by practitioners who understand calcium metabolism beyond the simplistic "take vitamin D for bones" advice that dominates public health messaging.
Most vitamin D supplements come as tablets or capsules — formats that require bile for absorption and offer no dosing flexibility. A 2000 IU capsule gives you exactly 2000 IU regardless of whether your blood levels need 1000 or 4000 to reach optimal range. Tablets contain binders, fillers, and coatings that add nothing to the therapeutic value. And almost none of them include K2, forcing you to buy a second supplement, take a second pill, and hope that the timing and ratio are appropriate. The result is either under-dosing, over-dosing, or incomplete dosing — all of which could be solved by a liquid format that combines both vitamins in a single drop-dose delivery.
Thorne Vitamin D3 + K2 delivers both vitamins in a liquid MCT oil base that maximises absorption of these fat-soluble nutrients without requiring dietary fat at the time of dosing. Each two-drop serving provides 1000 IU of vitamin D3 (cholecalciferol) — the more potent, better-absorbed form over D2 — alongside vitamin K2 as MK-4 (menatetrenone), the most clinically studied form of vitamin K. MK-4 activates osteocalcin, the protein that binds calcium into bone matrix, and matrix Gla protein (MGP), the protein that prevents calcium deposition in arterial walls. The drop format allows precise dose adjustment: two drops for 1000 IU maintenance, four drops for 2000 IU winter support, or as directed by your practitioner based on blood levels. A single 30 ml bottle provides hundreds of servings — months of daily use from one purchase. No capsules, no tablets, no fillers, no binders. Just two vitamins in oil.
Thorne is NSF Certified for Sport, third-party tested through four rounds of quality verification, and trusted by over 47,000 healthcare practitioners worldwide. No gluten, dairy, soy, artificial colours, or preservatives. Can be taken directly under the tongue, added to food, or mixed into beverages. Do not refrigerate.
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What it does
Benefits
- 01
Vitamin D3 (cholecalciferol) is the biologically preferred form of vitamin D — more potent and more effective at raising blood 25-hydroxyvitamin D levels than D2 (ergocalciferol), supporting normal calcium absorption, bone maintenance, muscle function, and immune system regulation
- 02
Vitamin K2 as MK-4 is the most clinically studied form of vitamin K for bone and cardiovascular health — it activates osteocalcin (which binds calcium into bone) and matrix Gla protein (which prevents calcium deposition in arterial walls), ensuring that the calcium absorbed through vitamin D reaches the right destination
- 03
The D3 + K2 combination addresses the complete calcium metabolism pathway — D3 increases absorption, K2 directs deposition — a synergy that neither vitamin achieves alone and that most standalone vitamin D supplements entirely neglect
- 04
MCT oil provides a lipid carrier that enhances absorption of both fat-soluble vitamins without requiring dietary fat at the time of dosing — the vitamins dissolve directly into the oil medium for immediate bioavailability
- 05
Vitamin D contributes to normal absorption and utilisation of calcium and phosphorus, the maintenance of normal bones and teeth, normal muscle function, and the normal function of the immune system
- 06
Vitamin K contributes to the maintenance of normal bones and normal blood clotting
Get the most from it
How to use
Take 2 drops one to three times daily, or as recommended by your healthcare professional. Invert the bottle and dispense individual drops directly under the tongue, onto food, or into a beverage. Two drops provide 1000 IU D3 — adjust dose based on your blood vitamin D level and practitioner guidance. For UK winter maintenance (October to March), 2000 to 4000 IU daily is commonly recommended for adults with confirmed insufficiency. Those with optimal levels may maintain on 1000 to 2000 IU daily. Periodic blood testing of 25-hydroxyvitamin D is recommended for anyone supplementing above 2000 IU daily. Do not refrigerate. Do not exceed recommended dose without medical guidance. Individuals taking anticoagulant medications (warfarin, acenocoumarol) should consult their doctor before supplementing with vitamin K, as it directly affects blood clotting pathways. Store in a cool, dry place away from direct sunlight.
What's inside
Ingredients
View full ingredient list
Vitamin D3 (as Cholecalciferol) 1000 IU per 2 drops, Vitamin K2 (as Menatetrenone / MK-4), Medium Chain Triglyceride Oil, Antioxidant (Mixed Tocopherols) Four ingredients. No capsule shell, no fillers, no binders, no anti-caking agents.
Common questions
Frequently asked
Why does this combine vitamin D with K2 rather than offering D alone?
Vitamin D3 increases calcium absorption, but K2 is needed to activate the proteins that direct that calcium to bone rather than soft tissue. The combination addresses both steps in the process, which is why many clinicians prefer it over D3 alone.
Should I test my vitamin D levels before starting this?
A baseline blood test is worthwhile. It confirms whether you are actually deficient, gives you a reference point to check progress, and helps a clinician determine whether a standard maintenance dose is appropriate for you or whether a higher therapeutic dose is needed.
Is this safe to take if I am on blood-thinning medication such as warfarin?
Vitamin K2 can interact with warfarin and similar anticoagulant medications by affecting clotting pathways. If you are on any anticoagulant, speak to your GP or prescribing clinician before starting this supplement.
How long before I notice a difference?
Vitamin D is a fat-soluble nutrient that builds up gradually. Blood levels typically rise over several weeks of consistent use. Bone-related benefits operate over months to years rather than days, so patience and a follow-up blood test at around three months are both sensible.
Who might not be suitable for this supplement?
People with hypercalcaemia, certain granulomatous conditions such as sarcoidosis, or primary hyperparathyroidism should avoid additional vitamin D without medical supervision. Those on anticoagulants should seek advice before taking K2, as noted above. Check with your doctor if you are pregnant or managing a chronic condition.
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