Pick up two calcium supplements and the fronts of the boxes say much the same thing. Turn them over and one lists calcium carbonate, another calcium citrate, a third splits its calcium across four compounds. That is not decoration.
The useful question is not which form wins. It is how much actual calcium you are getting, and whether your body is in a position to take it up.
Elemental calcium is the number that decides everything
Calcium never arrives as pure calcium. It is always bound to something else: a carbonate, a citrate, a lactate or an amino acid. Only part of that compound's weight is calcium itself, and that part is called elemental calcium.
So 500 mg of calcium carbonate is not 500 mg of calcium. Carbonate is roughly 40 per cent calcium by weight, which makes it about 200 mg. Calcium citrate is closer to 21 per cent. Calcium lactate is lower again, around 13 per cent. Identical weights on the label, very different amounts of calcium delivered.
A properly written label gives the elemental figure, usually in brackets after the compound. If it gives only the compound weight, you are being told less than you need. The rest of the panel deserves the same attention, and our label guide covers it.
The four forms, in practice
- Carbonate holds the most calcium per gram of the four, so it takes fewer capsules to reach a given amount. It needs stomach acid to dissolve, which is why the directions say to take it with food.
- Citrate carries less calcium per gram, but it absorbs with or without a meal and depends far less on stomach acid. That is the practical reason it tends to suit people on acid-reducing medication.
- Lactate is the calcium salt of lactic acid. Less calcium per gram than carbonate, readily soluble, and generally described as gentle on the stomach.
- Bisglycinate is calcium chelated to the amino acid glycine. It is usually well tolerated, and its elemental percentage varies between suppliers, so read the figure rather than assume it.
Tolerability is the honest differentiator here, not some dramatic gap in absorption. Taken sensibly and with food, the common forms sit closer together than the marketing suggests.
Why formulas blend several forms
A single-form product is a single set of trade-offs. Blending lets a formulator take density from one source, easier tolerance from another and a different dissolution behaviour from a third, so the capsule leans less on any one condition in the stomach. It also builds the elemental total from several places, which is why that total matters more than any single name in the list. A blend is not automatically better. It is a deliberate choice, and it should read like one.
Calcium does not work alone
Three nutrients come up constantly alongside it, and it is worth being precise about each. Vitamin D contributes to the normal absorption and utilisation of calcium; it has the best-established supporting role of the three. Magnesium contributes to normal muscle function. Vitamin K2 has a recognised role in the maintenance of normal bones.
None of that means one capsule has to carry all four. It does mean the picture is wider than a calcium figure — diet, sun exposure and whatever else you already take all sit inside it.
Smaller amounts, more often
The body takes up calcium more efficiently in modest amounts. Push much beyond roughly 500 mg of elemental calcium in one go and the proportion absorbed drops. Splitting your intake across the day therefore gets more out of the same total than taking it all at breakfast, which matters if you are working towards a daily figure.
Food counts towards that figure as well. Milk and yoghurt, calcium-set tofu, small fish eaten with the bones, leafy greens and fortified soy drinks all contribute, which makes a daily total easy to underestimate and easy to overshoot. A pharmacist can add up your diet and your supplements together in a few minutes. That is the right person to ask.
Our own CORE takes the blended route: calcium lactate, micronised calcium, eggshell calcium and calcium bisglycinate, with HCP casein hydrolysate and a marine extract that contains magnesium. Two capsules daily, with warm water before or after a meal. It contains egg and milk, so it is not suitable if either is a problem for you. It contains no vitamin D and no vitamin K2 — if you want those, they have to come from somewhere else.