What is calcium, and how much do you need?

Calcium is the most abundant mineral in the body. About 99 per cent of it sits in bone and teeth; the remaining one per cent works in blood and tissue.

What does calcium do?

The annex to Thai Ministry of Public Health Notification No. 447 (B.E. 2566) recognises several statements:

• Calcium is needed for the maintenance of normal bones and teeth
• Calcium contributes to the synthesis of bones and teeth
• Calcium contributes to normal blood clotting
• Calcium contributes to normal muscle function
• Calcium contributes to normal neurotransmission
• Calcium contributes to normal energy-yielding metabolism
• Calcium contributes to the normal function of digestive enzymes

How much per day?

Recommended intakes set by the US National Academies' Food and Nutrition Board, as published by the NIH Office of Dietary Supplements, are 1,000 mg a day for adults, rising to 1,200 mg for women over 50 and for everyone over 70.

The tolerable upper intake level is 2,500 mg a day for adults up to 50, and 2,000 mg for those over 50.

Where does it come from in food?

In Thai cooking, the easy sources are small fish eaten with the bones, dried shrimp, shrimp paste, firm tofu, black sesame, dark leafy greens such as noni leaves (bai yo) and water mimosa (phak krachet), and milk and dairy.

Some vegetables are high in oxalate, which binds calcium, so eating a variety is better than relying on one.

What helps absorption?

Vitamin D contributes to the normal absorption of calcium and phosphorus. That is why the two are so often discussed together.

The body absorbs calcium more efficiently in amounts up to around 500 mg at a time, so splitting the day's intake across two occasions makes more sense than taking it all at once.

How do the forms differ?

Calcium carbonate carries a high proportion of calcium per unit weight but relies on stomach acid, so it is usually suggested with food.

Calcium citrate carries less per unit weight but depends less on stomach acidity. Calcium L-threonate also carries a low proportion of elemental calcium, around 8 per cent.

Whichever the form, the figure to compare is the elemental calcium given in brackets on the label.

What should you watch out for?

Large amounts of calcium interfere with iron and zinc absorption, so separating them in time is easier than taking them together.

If you take prescription medication, speak to a doctor or pharmacist before supplementing.

Dietary supplements are not intended to prevent, treat or cure any disease.