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Calcium
An essential mineral with ten authorised EU health claims, from bones and teeth to muscle function, blood clotting and neurotransmission. Almost all of the calcium in your body, 99% of it, is stored in bone. We serve it in one formula, at the full reference amount, and it is the reason that formula keeps away from the one that carries iron.
WHAT WE ARE ALLOWED TO SAY
Ten claims. All of them authorised.
These are the ten authorised EU claims for calcium in our file, and we do not paraphrase them into something that sounds stronger. The first eight need the product to be at least a source of calcium under Regulation (EC) 1924/2006. The last two are Article 14 claims: they need at least 120 mg of calcium a serving, and the combined one also at least 0.75 µg of vitamin D. CORE-07 serves 800 mg of calcium, which is 100% of the NRV, and 25 µg of vitamin D3.These are the ten authorised EU claims for calcium in our file, and we do not paraphrase them. Eight need the product to be at least a source of calcium; the two Article 14 claims need 120 mg of calcium a serving, and the combined one 0.75 µg of vitamin D. CORE-07 serves 800 mg and 25 µg of D3, which clears all of them.
The two Article 14 claims are about bones, and the first links too little calcium in your diet with a higher risk of osteoporosis. Neither says calcium treats or prevents osteoporosis, and none of the ten is a claim about fractures. Our calcium notes also mention a third claim, under Regulation (EC) 983/2009, for calcium with vitamin D and bone mineral loss in postmenopausal women, but it has no entry in our claims register, so we do not quote it. Our file also mentions calcium as a cofactor in making melatonin. That is not a claim, and no VION sleep formula carries calcium.
WHY CITRATE
It does not need your stomach acid.
The claims attach to calcium, not to a particular salt, so the form is not a claim argument and we do not use it as one. We chose citrate because it is absorbed without stomach acid, so it works with or without a meal, and because our file marks it as stable in liquid. VION doses are liquid.
The most calcium per gram of salt, about 40%, and the cheapest. It needs stomach acid, so it has to be taken with food, it causes more constipation, and acid-reducing medication cuts how much of it you absorb.
Our notes record the highest bioavailability of the three, about 35%, and it is the form used in studies of bone in children. It is also the most expensive, and it is not what we chose.
Absorbed without stomach acid, with or without food, and not affected by acid-reducing medication. Our notes record it as the better form for combining in a liquid shot.
Better absorption is what our notes report. It is not an authorised claim, so you will not read it on a label. Our own files do not agree on the figure for citrate either: one records 22 to 27% absorbed, another 25 to 35%. And there are forms we rule out: calcium oxide, which is irritant, and calcium from oyster shell, dolomite or coral, because of the risk of lead.Better absorption is not an authorised claim, and our files record anywhere from 22 to 35% absorbed for citrate. We rule out oyster shell, dolomite and coral because of the risk of lead.
WHERE IT APPEARS
One of the twenty-nine carries calcium.
CORE-07, the bones formula, serves 800 mg with dinner, next to vitamin D3, K2 and magnesium. It is kept to the evening because iron is served in the morning. There is an open point we would rather write down: our file asks for no more than 500 mg in a single dose, because absorption saturates, and flags this citrate to be split across the day. The formula pours all 800 mg in one evening dose, and that is pending clinical review.
THE CEILING
2,500 mg a day, food included.
The EFSA upper limit for calcium is 2,500 mg a day for adults, and it counts what you eat as well as what you take. Our file assumes an average Spanish diet already brings about 800 mg, so if calcium ever sat in two formulas at once, the engine would cap the total from formulas at 1,500 mg. Today only CORE-07 carries it, at 800 mg. That is well under the EFSA limit, but above the 500 mg a day Germany's BfR proposes as a maximum from supplements.The EFSA limit is 2,500 mg a day, food included, and an average Spanish diet brings about 800 mg. CORE-07 serves 800 mg, above the 500 mg Germany's BfR proposes for supplements.
If calcium ever sat in two active formulas, our engine notes cap the total from formulas at 1,500 mg a day, to leave room for your diet under the 2,500 mg limit. With vitamin D3 in the same plan, our interaction file keeps supplemental calcium at or under 1,000 mg a day. Our file also flags vitamins D3 and K2, magnesium, boron, phosphorus and manganese as ingredients that work on bone too: a risk of doubling up on the same job.
Constipation, bloating and gas, more often with carbonate. Absorption saturates: our notes record 36% absorbed at 300 mg and 28% at 1,000 mg, which is why doses are best kept to 500 mg or less. High blood calcium, above 10.5 mg/dl, is rare with oral supplements when your kidneys work normally, and shows as low muscle tone, frequent urination, heart rhythm problems and kidney stones. Supplements above 1,000 mg a day have been linked to more kidney stones, and some meta-analyses suggest a 15–16% higher cardiovascular risk with calcium taken without vitamin D, a point that is still disputed.
Contraindicated with high blood calcium, hyperparathyroidism or sarcoidosis. Our file also lists advanced chronic kidney disease (stages 3–5), because of the risk of vascular calcification and high blood calcium; the clinical consensus it cites (KDIGO) limits total elemental calcium there to under 1,500 mg a day, phosphate binders included. Active kidney stones block the pairing with vitamin D3. With a history of calcium oxalate kidney stones, avoid doses over 500 mg without supervision and prefer calcium from food. With a heart condition or an arrhythmia the evidence is disputed: avoid single doses over 500 mg. If you take anticoagulants (warfarin, acenocoumarol, apixaban) or antiplatelet drugs, ask your doctor first: our label warning says calcium can change their effect, although our calcium file records no direct interaction with warfarin and points instead at the vitamin K2 it is often paired with. With cancer there is no absolute contraindication, but observational data link dietary intakes above 1,500 mg a day, from dairy, with more advanced prostate cancer. Our file sets no specific restriction for liver disease, and none for calcium itself in pregnancy or breastfeeding. Under 18, the upper limit is 2,500 to 3,000 mg a day depending on age. There is no mandatory EU label warning specific to calcium beyond the general one (do not exceed the recommended daily dose); the anticoagulant warning above is our own label warning. It contains none of the fourteen allergens that must be declared in the EU.
WHAT IT REACTS WITH
Documented pairs, not hunches.
Calcium is one of the 140 ingredients in our library, so it has 139 possible partners. We have documented 11 of them, out of the 443 pairs on file, plus six medicines. Five are partners that can share a dose, four are binders to keep apart, and two are about how much you take.
Our file puts calcium, vitamin D3 and K2 together on purpose: D3 raises how much calcium your gut absorbs, and our file describes K2 as directing that calcium towards bone. That is why the engine adds K2 and magnesium whenever vitamin D3 enters a plan, and why the D3 pair keeps supplemental calcium at or under 1,000 mg a day; that pair is still marked for review. Boron reduces how much calcium you lose in urine, and inulin, FOS and oligofructose help your gut absorb more of it.
Activated charcoal never shares a dose with calcium and stays at least 3 hours away. White clay, konjac glucomannan and psyllium bind or trap it, so they are kept at least 2 hours apart. Iron is kept to the morning and calcium to the evening: in the same meal, 300 mg of calcium or more can cut the iron you absorb by around half. That rule comes from our calcium file and the formula timings, not yet from a documented pair, and the same file asks for 2 hours between calcium and zinc at 25 mg or more. Caffeine raises how much calcium you lose in urine; above 300 mg a day it is watched in postmenopausal and osteoporosis profiles, not excluded.
Calcium binds several medicines in your gut. Bisphosphonates such as alendronate: take them fasting, wait at least 30 minutes, and keep calcium at least 2 hours away. Levothyroxine: at least 4 hours apart. Quinolone antibiotics such as ciprofloxacin: at least 2 hours before or 6 hours after the calcium. Tetracyclines such as doxycycline: at least 2 hours apart. Digoxin: levels monitored, and high doses of calcium avoided. Acid reducers such as omeprazole: citrate, the form we use, is not affected, carbonate is. Our file also lists integrase inhibitors such as dolutegravir, thiazide diuretics, lithium and long-term corticosteroids, which are not in the pair table yet. If you take any of them, ask your doctor before starting.
443 of the 9,730 possible pairs in our library 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.443 of the 9,730 possible pairs in our library 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.
SOURCES
Everything on this page, with its reference.
Reviewed by VION nutrition team · last reviewed 16 September 2026
140 INGREDIENTS · 64 IN USE TODAY
Every one of them has a page like this.
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.