Calcium

The most abundant mineral in the body, almost all of it in bone — which doubles as the reserve the body draws on to keep blood levels steady. Because that reserve is defended so tightly, a blood test tells you very little about whether your intake is adequate.

Ninety-nine per cent of it is structural — bone and teeth. The remaining one per cent runs muscle contraction, nerve signalling and blood clotting, and the body will strip bone to keep that fraction steady.

• Dairy
• Fortified plant milks
• Tinned sardines with bones
• Tofu set with calcium
• Kale and bok choy
• Almonds

Needs vitamin D. Absorbed better in doses of 500 mg or less at a time.

1,000 mg · 1,200 mg for women over 50 and men over 70 for most adults. The upper limit, past which harm becomes likely, is 2,500 mg.

Reference intakes are population figures. Pregnancy, illness, age and medication all move an individual’s needs, which is one of several reasons this page is information rather than advice.

Most at risk: Postmenopausal women, people avoiding dairy without replacing it, and those with coeliac disease.

Low intake, particularly without dairy; poor absorption when vitamin D is low; coeliac disease and other malabsorption; and after menopause, when falling oestrogen accelerates bone loss regardless of intake.

Blood levels stay normal at the expense of the skeleton, so shortage shows as reduced bone density over years rather than symptoms now. Severe acute low calcium causes muscle cramps and tingling.

Every sign here has other, often likelier, explanations. A list of symptoms is a reason to look into something, never a diagnosis.

Serum calcium is tightly regulated and will usually look normal even when intake has been inadequate for years — the body takes what it needs from bone. Bone density scanning, not a blood test, is what assesses the consequence.

Dairy, fortified plant milks (shake the carton, the calcium settles), tinned fish with the bones in, tofu set with calcium, and leafy greens — though spinach binds its own calcium and contributes little. Spreading intake across the day absorbs better than one large amount.

Carbonate needs stomach acid and is best taken with food; citrate does not and suits anyone on acid suppression. Absorption is better in doses of 500 mg or less. Calcium supplements interfere with iron, zinc and some antibiotics — separate them by a couple of hours.

Supplemental excess causes constipation and kidney stones, and can interfere with iron and zinc absorption. Some evidence links high supplemental — not dietary — calcium to cardiovascular risk.

Interactions: Reduces absorption of iron, zinc and several antibiotics — separate them by two hours.