Whenever possible, we should try to choose a diet that includes adequate amounts of all the essential nutrients. In the case of calcium, this means consuming enough dairy products and/or relying heavily on relatively few foods --such as canned salmon and sardines with the bones, kale, collards, mustard and turnip greens and broccoli--to get 800 milligrams a day.
Recent studies have found dietary intakes of many Americans, particularly women, to be well below that level. As the high incidence of osteoporosis moves into the limelight, attention has focused on the use of calcium supplements as an alternative.
There is quite a collection to consider. The most common preparations are the calcium salts: carbonate, gluconate, lactate and phosphate. All but one are sold strictly as calcium supplements. The exception is calcium carbonate, which is also used as an antacid. Tums is the most well-known. Be aware, however, that most other antacid preparations, including the popular brands Maalox, Mylanta, Gelusil and Rolaids, do not contain calcium. And some have a lot of sodium, so check the label on these products carefully.
Some meal and dolomite also provide calcium. Because they can be contaminated with toxic metals such as lead or mercury, we do not recommend them.
Daily multiple-vitamin supplements usually contain no calcium. The exceptions are some with added minerals. Again, read the label. Calcium levels in these products generally range from 40 to 60 milligrams. It is not practical to count on this type of supplement for more than a minor contribution to your calcium intake.
Besides calcium salt, supplements may also contain vitamin D, phosphorus and/or magnesium. Unless you are housebound or get very limited exposure to sunlight, you probably don`t need extra vitamin D. As for phosphorus, nowadays there is concern that the average American is getting too much of it, particularly from processed foods and soft drinks. Getting more in the form of a supplement is probably unnecessary. And there is scant support for claims that magnesium enhances calcium absorption or utilization.
The major difference between the various calcium supplements is concentration--meaning how much calcium itself is found in a given amount of a calcium salt. Carbonate is the most concentrated form at 40 percent calcium, followed by tricalcium phosphate at 39 percent. Dicalcium phosphate provides 29 percent, and lactate 13 percent. Gluconate trails at only 9 percent calcium. These figures can mean the difference between taking one or two tablets or downing as many as 10 or 12 to get the same dose of calcium.
Unfortunately, it is harder than it should be to learn how much calcium there is in each tablet. On one bottle we saw, ``500 milligrams`` was prominently displayed on the front label. But a careful reading of the side panel revealed that the 500 milligrams referred to the total compound, calcium carbonate. Each tablet contained only 200 milligrams of calcium. In another case, the main label said ``1,000 milligrams,`` but elsewhere on the bottle it indicated that it took three pills to get that dose.
Although the various supplements differ in concentration, with one exception they are believed to be equally effective. Calcium carbonate, currently the most popular of the supplements, may be poorly absorbed by many older people. This is related to the gradual decline in stomach acid that tends to accompany advancing age.
What`s the best time to take a supplement? Absorption is probably better on an empty stomach. But manufacturers recommend taking supplements with meals because people are more likely to remember it that way, and it minimizes the chance for stomach upset.