A standard calcium supplement tablet contains 12.5 mmol calcium. The amount of calcium absorbed is relatively low, with most of a daily dose appearing in the stool.
Specimen: The study used 4 days of pooled fecal samples. However, the author found that the rate of excretion was relatively constant so that a smaller interval could be used.
Parameters:
(1) fecal calcium density (calcium in mmol per gram dry weight feces)
calcium intake in mmol per day =
= (26.75 * (fecal calcium density)) + 0.626
The author also gave an equation for estimating fecal calcium density based on daily calcium intake:
fecal calcium density =
= (0.0301 * (calcium intake in mmol/day)) + 0.114
If this equation is re-arranged:
calcium intake in mmol/day =
= (33.22 * (fecal calcium density)) - 3.787
Limitations:
• The study assumed constant calcium intake. The equation should work for a person who is always compliant or always noncompliant, but it might not work for a person who is intermittently so.
• The technique is dependent on the accuracy of the measurement. A small change in the fecal calcium density can result in a large change in the estimated intake. The stool sample has to be dried to the same degree each time.
