The girls often have their blood drawn before breakfast. They also have to collect their own urine and fecal samples in special containers. The researchers then analyze the calcium content of all these samples and calculate how much dietary calcium got into the bloodstream, how much calcium was excreted, and how much calcium each girl retained. The girls who come to Camp Calcium don't really mind collecting the samples. We take in calcium through our diet, and lose it from the body mainly in urine, feces, and sweat.
Most dietary calcium is absorbed into the bloodstream in the small intestine.
The body depends on adequate calcium from the diet both to build healthy new bone and to avoid excessive loss of calcium from bone. The girls spend one day of camp at the hospital, where they get their bones scanned by a machine that measures bone density. At the hospital the researchers also give the girls two special, traceable forms of calcium and then draw their blood at regular intervals over a period of many hours. The researchers measure these calcium tracers in blood, urine, and fecal samples from subsequent days. The results of these studies show how much calcium is absorbed in the digestive tract, how the kidneys handle calcium, and how much calcium goes into bone.