Most people, particularly the elderly, do not get enough calcium in their diets. Insufficient calcium may contribute to osteoporosis and high blood pressure. Dietary sources include dairy products, leafy green vegetables, and fish, but supplementary calcium tablets are often recommended as well. A bewildering number of preparations are available. Which one you should choose?

The first thing to know is that while it is the calcium that your body needs, the calcium always comes in combination with another substance, such as carbonate, citrate, lactate, or gluconate, which are technically known as calcium salts. Thus a 500 milligram (mg) Tums tablet, which consists of calcium carbonate, contains 200 mgs of calcium, the other 300 being carbonate. This distinction is important, because as shown in the table below, an 'Os-Cal 500' tablet has 1,250 mg of calcium carbonate, and 500 of calcium. And a 500 mg tablet of calcium gluconate contains only 45 mg of calcium. The table below shows some of the available preparations, including the dose, how much calcium each pill contains, and the cost (average wholesale price) for 500 mgs of calcium.

Calcium Salt	Trade Name	Dosage	Calcium per tablet/capsule	Cost for 500 mg calcium
Carbonate	Tums	500 mg tablet	200 mg	7 cents
	Chooz	500 mg tablet	200 mg	24 cents
	Generic	650 mg tablet	260 mg	3-18 cents
	Tums E-X	750 mg tablet	300 mg	7 cents
	Alka-Mints	850 mg tablet	340 mg	5 cents
	Os-Cal 500	1,250 mg tablet	500 mg	11 cents
	Caltrate 600	1,500 mg tablet	600 mg	9 cents
Citrate	Citracal	950 mg tablet	200 mg	17 cents
Lactate	Generics	325 mg tablet	42 mg	18-27 cents
Gluconate	Generics	500 mg tablet	45 mg	43-83 cents
		975 mg tablet	88 mg	15-51 cents

Another factor to consider is how well the different calcium salts are absorbed. In general, calcium citrate is absorbed a little better than calcium carbonate, but the differences are relatively small. Calcium supplements should be taken with food to maximize absorption.

Can you take too much calcium? Yes. The side effects of high doses of calcium are constipation, stomach bloating and excessive gas. More important is an increased risk of kidney stones.