By Curtiss Hunt
Folks who want healthy bones long have been told to get plenty of calcium. After all, the body compensates for an inadequate calcium intake by drawing calcium out of bones and putting it into the blood stream.
But how much calcium do we need?
About 10 years ago, the National Academy of Sciences asked a group of experts in calcium nutrition to come up with a new estimate of how much calcium most healthy people need in their diets. Specifically, they were asked to look at all of the available research information and establish an Recommended Dietary Allowance for calcium.
The panel of experts reviewed several types of studies, including those where researchers measured how much calcium a subject ate and how much they excreted. These studies try to find the point where the amount of calcium lost through excretion equals the amount of calcium eaten. This point of neutral balance is one way of estimating the calcium requirement.
As can be imagined, it is very difficult to measure all of calcium that is consumed and all that is excreted. For example, a study volunteer may fail to eat every last crumb of his or her required meals. Also, the scientist may have difficulty finding and using the scientific machinery that is sensitive enough to detect small amounts of calcium in the excretion samples. And, of course, this type of study is expensive to carry out, so few have been attempted.
Unfortunately, the experts couldn't find enough useful research information to set an RDA for calcium. In the end, they settled on giving the public a recommendation called adequate intake, which is a more tentative reference because of the quality of the available information upon which it's based. Today's AI for calcium is 1,000 milligrams per day for those 19 to 50 and 1,200 milligrams per day for those 51 or older.
But help is on the way for a better estimate of the calcium requirements. During the past 20 years, scientists at the Grand Forks Human Nutrition Research Center collected thousands of diet and excretion samples from persons who volunteered to live at the center, usually for six months.
The volunteers had their own private bedrooms and at mealtime in the dining room, they were very careful to eat every morsel of their food, every day, every week and every month. Any spills were reported immediately to our highly trained kitchen staff.
Afterward, the scientists in the center used special instruments capable of measuring tiny amounts of mineral, including calcium, in the collected diet and excretion samples.
Because such great care was taken in all phases of these human studies, the scientists were able to answer many important questions about how minerals are used by the body.
In 19 of those studies, center scientists measured calcium intakes and calcium excretion in a total of 155 volunteers, ages 19 to 75. I combined all of this very high-quality calcium balance data and was able to come up with a new estimate of the calcium requirement. I relied on the expertise of the center statistician, LuAnn Johnson, to create the statistical program needed to mesh hundreds of data points.
After the information was assembled, we discovered that the body tries to maintain a relatively stable amount of calcium within a broad range of typical daily calcium intakes - from 415 milligrams on the low end to 1,740 milligrams on the high end. When fed the lower amounts, the body was more efficient in keeping calcium. When fed the higher amounts, the extra calcium was simply eliminated.
Using our data, we predicted that nearly everyone would be in neutral calcium balance if they ate 1,035 milligrams of calcium each day on average. Our findings recently were published in the American Journal of Clinical Nutrition. The information probably will be useful in setting the next RDA for calcium when the next panel of experts meets.
Our research suggests that the RDA for all adults 19 and older should be 1,035 milligrams per day. This intake of calcium is not difficult to achieve. It is very close to the amount of calcium found in 3 cups of whole or skim milk or in five slices (5 ounces) of Cheddar cheese.