Calcium

Calcium is the most abundant mineral in the human body, with roughly 99 per cent stored in bone and teeth. The remaining one per cent circulates and does the signalling work, and the body defends that circulating level tightly — drawing on bone if intake falls short.

Dairy is the richest common source, but tinned fish with bones, tofu set with calcium, fortified plant milks, leafy greens and nuts all contribute meaningfully. In the UK, white and brown flour is fortified with calcium by law, so bread is a quiet contributor for most people.

Supplement forms differ in practical ways. Calcium carbonate is cheapest and highest in elemental calcium at around 40 per cent, but needs stomach acid to dissolve, so it must be taken with food. Calcium citrate is around 21 per cent elemental, costs more, but absorbs regardless of stomach acid and is gentler on digestion.

In bone, calcium combines with phosphate to form hydroxyapatite, the mineral crystal that gives the skeleton its hardness. Bone is not static — it is continuously broken down and rebuilt, and calcium availability affects that balance.

The circulating fraction is what makes muscles contract. Calcium release inside muscle cells triggers contraction, and its removal allows relaxation, which is why magnesium and calcium are so often discussed as opposites.

Absorption depends heavily on vitamin D, and is limited per dose to around 500 mg regardless of how much you take. It also depends on where the calcium ends up, which is where vitamin K2 enters the picture: D increases absorption, K2 influences whether that calcium is directed into bone.

Calcium's essentiality is beyond question, and adequate intake through the years when bone is being built is well established as important for peak bone mass.

Supplementation in adults is less clear-cut than it was once presented. Large reviews have found that calcium supplements produce only small increases in bone density and that the effect on fracture risk is modest at best, particularly in people whose dietary intake is already reasonable.

There has also been research debate about whether high-dose calcium supplements, as distinct from calcium from food, carry cardiovascular downsides. The findings are contested rather than settled, but combined with the modest benefit, the sensible conclusion is to prioritise food sources and reserve supplements for people who genuinely cannot reach adequate intake.

Calcium from food is safe and unremarkable. Supplements commonly cause constipation and bloating, particularly carbonate, and citrate is generally better tolerated.

High supplemental intake increases the likelihood of kidney stones in people prone to them, and there is ongoing research debate about cardiovascular effects of high-dose supplements specifically.

Calcium reduces absorption of several types of medicine and of iron and zinc if taken together. Separate doses by a couple of hours. Speak to your doctor before use if you take regular medication.