Calcium supplements

Several dietary studies suggest that in many population groups, calcium intake is inadequate, particularly in women. As few as 10 per cent of elderly people are getting enough calcium to prevent bone loss and are likely to benefit from supplements. Pregnant and breastfeeding women, adolescent girls, postmenopausal women and vegans may also benefit.

What type to take

Calcium supplements are among those most often prescribed by doctors as calcium deficiency is relatively common. They contain different amounts of calcium and are available in various forms including calcium carbonate (which contains 40 per cent calcium), calcium aspartate, calcium citrate (21 per cent calcium), calcium gluconate (9 per cent calcium) and calcium lactate (13 per cent calcium). While multivitamins do contain some calcium, the amount is not usually sufficient to meet daily requirements and separate calcium supplements are more useful.

Bonemeal, dolomite and oyster shells are common sources of calcium, but they should be avoided as they may be contaminated with lead and cadmium, which can be toxic. Antacids are also good sources of calcium, but those containing aluminum or sodium should be avoided as aluminum inhibits calcium absorption and sodium can raise blood pressure. Calcium citrate, which is an acidified form of calcium supplement, is absorbed better than calcium carbonate. This is particularly important in older people who have low stomach acid. Calcium lactate and calcium aspartate are also well-absorbed. Calcium carbonate may cause side effects such as nausea, gas and constipation; but taking it in divided doses with meals may reduce these side effects and improve absorption.

Calcium supplementsWhen to take calcium supplements

Absorption of calcium from supplements is considerably reduced in people who have low stomach acid unless the supplements are taken with food. In general, it seems that calcium supplements are better absorbed if they are taken with a meal, although this depends on the type of food eaten at the meal, for example, less calcium will be absorbed if supplements are taken with foods high in calcium, insoluble fiber and oxalates. A 1989 study showed that a light meal improved calcium absorption from milk, calcium carbonate and calcium-citrate-malate sources. However, calcium may decrease the absorption of other minerals such as zinc. Some calcium supplements can interfere with iron absorption, although this does not seem to be the case with calcium citrate and calcium ascorbate as they are acidic.

Some experts advise taking two-thirds of the daily calcium dose at bedtime and the rest in the morning. Others recommend dividing the dose into four parts; i.e. with meals and at bedtime. As bone loses calcium at night, some experts recommend taking supplements then to maintain blood calcium levels.

Calcium and magnesium

If you take a calcium supplement, you should also take a magnesium supplement. This helps to avoid constipation and to balance the effect of calcium on the electrical impulses in the nerves and muscles. Calcium and magnesium work together as mild neuromuscular relaxants. Some experts recommend taking calcium and magnesium in a 2:1 ratio while others suggest 1:1.

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