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Vitamin D3
A fat-soluble vitamin that your body turns into a hormone in two steps, first in the liver and then in the kidney. The active form switches on the proteins that carry calcium across your gut, and takes part in bone mineralisation, immune function and cell differentiation. It carries seven authorised EU health claims, EFSA has set an upper limit of 100 µg a day, and it sits in nine formulas, from 10 to 62.5 µg.
WHAT WE ARE ALLOWED TO SAY
Seven claims. All of them authorised.
Our file holds these seven wordings in Spanish only, so what you read here are literal translations of them, and we do not paraphrase them into something that sounds stronger. All seven carry the same condition: the product has to be at least a source of vitamin D under Regulation (EC) 1924/2006. The NRV is only 5 µg, so even our smallest dose, 10 µg, is 200% of it.Literal translations of the Spanish wordings on file. We do not paraphrase them. All seven need the product to be at least a source of it. Our smallest dose is 200% of the NRV.
Vitamin D has no authorised claim for your thyroid or your testosterone, and we do not use it as one. In Functional thyroid and Autoimmune thyroid our files do not record why vitamin D is there, and none of its seven claims mentions the thyroid. In Low testosterone our notes list it for hormonal support, which is not a claim, and the testosterone claim in that formula belongs to the zinc next to it. The seven claims attach to vitamin D in general, not to D3 in particular.
WHY CHOLECALCIFEROL
The claims are the same. The evidence points one way.
The seven claims attach to vitamin D, not to one form of it, so the form is not a claim argument and we do not use it as one. Our file names cholecalciferol, vitamin D3, as the form of choice over ergocalciferol, vitamin D2: a 2012 meta-analysis on file found that D3 raises 25(OH)D, the marker a blood test measures, about 1.7 times more. It dissolves in oil rather than water, and our form file marks it as stable in liquid.
Our file records it as less effective than D3 at raising the 25(OH)D in your blood, by about 1.7 times in the 2012 meta-analysis. We do not use it.
The form in all nine of our formulas. Our notes say it is usually made from lanolin, which comes from sheep, so our file marks vitamin D3 as not suitable for a vegan diet. A vegan version from lichen exists. Which one our supplier uses is not documented yet.
Our form file lists light and oxygen as sensitivities and gives it a neutral taste. It dissolves in oil, not water. How that is handled in a liquid dose between production and your cartridge is not documented yet.
Our figures on how it behaves in your body do not all agree. Our notes put absorption at 60 to 80%, and say it rises by 32 to 50% when you take it with a meal that contains fat, which is why most of our formulas serve it with food. Your blood level of 25(OH)D takes weeks to move: our pharmacokinetic file says 2 to 4 weeks, our ingredient notes say 4 to 8 weeks to settle, with a half-life of about 15 days, and the two have not been reconciled yet. None of this is an authorised claim, and there is no claim that D3 works better than D2.Our notes put absorption at 60 to 80%, higher with a meal that contains fat. How fast your blood level moves is given as 2 to 4 weeks in one file and 4 to 8 in another. None of this is a claim.
WHERE IT APPEARS
Nine of the twenty-nine carry vitamin D3.
Always cholecalciferol, and mostly 25 µg. It goes from 10 µg in Daily athletic to 62.5 µg in D3 / K2, a dose for refilling low vitamin D for 12 weeks after a blood test. Most serve it with food, because it needs some fat. Functional thyroid is the exception: it goes before breakfast, even though our notes say vitamin D is better absorbed with a meal. Autoimmune thyroid and Low testosterone are still in development, the other seven are pending clinical validation, and each has its own exclusions, listed on its page.
THE CEILING
100 µg a day, across everything you take.
EFSA's upper limit for adults is 100 µg a day, and our file notes that it covers pregnancy and breastfeeding too. The engine adds up your vitamin D across every formula and blocks any addition that would reach or pass that limit. The most conservative reference in our file is the German BfR's proposed maximum for a supplement, 20 µg a day, and every formula except Daily athletic goes above it on its own. Our notes add a stricter rule: with vitamin D in three formulas at once, no more than 50 µg in total without clinical approval. That rule is not written into the engine yet.The limit applies to your total, not to each formula on its own. The German BfR reference is 20 µg a day for a supplement, and eight of our nine formulas go above it.
D3 / K2 at 62.5 µg leaves room for one of our 25 µg formulas, not two. Autoimmune thyroid and Low testosterone carry 50 µg each: together they reach the limit, and next to D3 / K2 either one passes it, so the engine will not add it.
Our file lists what an excess does: high blood calcium, calcium in the urine, nausea, muscle weakness, kidney stones and calcium deposits in soft tissue. It calls toxicity rare below 250 µg a day, and treats a blood 25(OH)D above 150 ng/ml as a sign of it. That is why the highest dose runs for 12 weeks and is then checked against a new blood test.
Our file treats high blood calcium and active calcium kidney stones as relative contraindications, and the same for sarcoidosis, lymphoma, primary hyperparathyroidism and granulomatous tuberculosis, where our notes say active vitamin D can be made outside the kidney and push your calcium up. Ask a doctor first if you have liver disease, where the first conversion step may not work and our notes prefer calcifediol under supervision; advanced kidney disease, where they point to active forms such as calcitriol or paricalcitol under a kidney specialist; a heart condition or arrhythmia, especially if you take digoxin; or cancer, where they advise against high doses without supervision because the data are mixed. Our file considers it safe in pregnancy and breastfeeding up to 100 µg a day. Under 18 the limit is adjusted by age: 63 µg a day from 1 to 3 years, 75 µg from 4 to 8, and the adult 100 µg from 9. Our label warning asks you to talk to your doctor if you take anticoagulants such as warfarin, acenocoumarol or apixaban, or antiplatelets, because it may change their effect, although our ingredient notes record no relevant direct interaction. Above 25 µg, our notes advise asking a doctor if you take thiazide diuretics or cardiac glycosides such as digoxin, which applies to D3 / K2, Autoimmune thyroid and Low testosterone.
All nine are ruled out if you take a vitamin K antagonist such as warfarin. D3 / K2 and Bones & joints are also ruled out with high blood calcium or sarcoidosis; Immunity with an autoimmune condition, immunosuppression or liver disease; Acute immunity with an autoimmune condition, immunosuppression or severe atopy; Cold symptom support with an autoimmune condition, immunosuppression or pregnancy; Functional thyroid with liver disease, overt hyperthyroidism, thyroid nodules under investigation or pregnancy; Autoimmune thyroid with liver disease, overt hyperthyroidism or pregnancy; Daily athletic and Low testosterone with liver or heart disease, a thyroid disorder, hyperandrogenism, sedative medication, pregnancy, breastfeeding or if you are under 18, and Low testosterone also for women and with prostate cancer. D3 / K2 is the only formula carrying it that our pregnancy rule allows.
WHAT IT REACTS WITH
Documented pairs, not hunches.
Vitamin D3 is one of the 140 ingredients in our library, so it has 139 possible partners. We have documented twelve of them, out of the 443 pairs on file: seven that work alongside it, and five that need care.
Vitamin D raises how much calcium you absorb. Our pair notes say K2 directs that calcium to bone, and that without K2 an excess of vitamin D may be linked to calcium deposits in blood vessels. Magnesium is needed by the enzymes that activate vitamin D, and our notes link low magnesium to vitamin D that does not respond to supplements. So whenever vitamin D3 is in your plan, the engine recommends K2 and magnesium alongside it. Calcium is one of the five that need care: our notes pair it with K2 and magnesium, keep supplemental calcium at 1,000 mg a day or less, and block the combination if your profile flags high blood calcium, active kidney stones or hyperparathyroidism. Bones & joints carries all four, with 800 mg of calcium. D3 / K2 carries vitamin D3, K2 and magnesium.
Activated charcoal can cut how much vitamin D you absorb by 30 to 90%, so it never shares a dose and stays at least 3 hours away. Konjac glucomannan, psyllium husk and kaolin clay also lower its absorption and are kept at least 2 hours apart. No VION formula carries any of the four, so that matters if you take them separately.
No drug pair for vitamin D3 is in our drug table yet. Our ingredient notes list thiazide diuretics such as hydrochlorothiazide, which raise the risk of high blood calcium; digoxin, which high calcium can make more toxic to the heart; anticonvulsants such as phenytoin, phenobarbital and carbamazepine, which speed up its breakdown; systemic steroids such as prednisone; orlistat, which lowers its absorption; and statins, whose effect high doses of vitamin D may reduce. Our label warning adds anticoagulants and antiplatelets. If you take any of these, talk to your doctor before starting a formula that carries it.
The other pairs that work alongside it are zinc, which shares six of its formulas; inulin, which only Digestion & microbiome carries; and boron, manganese and inactivated probiotics, which no formula carries today. Our ingredient notes also mention vitamin A, which in excess may blunt vitamin D's effect on bone, but it is not in our table as a pair yet, and nor are selenium, iodine, vitamin C or the botanicals it shares formulas with. Across the library, 443 of the 9,730 possible pairs are documented, which is 4.55%. The rest are not "safe", they are simply unchecked, and we would rather write that down than let the number look like a badge.Vitamin A, selenium, iodine, vitamin C and the botanicals it shares formulas with are not in our table as pairs with it yet. Across the library, 443 of the 9,730 possible pairs are documented, which is 4.55%. The rest are not safe, they are simply unchecked.
SOURCES
Everything on this page, with its reference.
Reviewed by VION nutrition team · last reviewed 16 September 2026
140 INGREDIENTS · 64 IN USE TODAY
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What it is, what we are allowed to say about it, which formulas carry it, what it reacts with and where each of those statements comes from. No proprietary blends, no hidden amounts.