The suggested levels featured some extrapolation from North American data for adults and by using coefficients to derive childhood and infant levels.
The levels accounted for an estimated 40 mg of calcium per day lost through perspiration.
“For infants (7–11 months), an AI (Adequate Intake ) was derived by extrapolating the average amount of calcium absorbed by exclusively breast-fed infants (120 mg/day) using isometric scaling and assuming an absorption of 60 %, and was calculated as 280 mg/day,” the Panel on Dietetic Products, Nutrition and Allergies (NDA) wrote in its Dietary Reference Values (DRV) work.
“The AR for children was derived using the factorial approach. The total quantity of calcium required for bone accretion and replacement of endogenous losses was adjusted for percentage absorption to derive PRIs (Population Reference Intake) for children aged 1–3, 4–10 and 11–17 years of 450, 800 and 1 150 mg/day, respectively.”
“The PRI for young adults (18–24 years), who still accumulate calcium in bones, is 1 000 mg/day. This is the intermediate value between children aged 11–17 years and adults. Taking into consideration adaptive changes in calcium metabolism that occur during pregnancy and lactation, the PRI for non-pregnant women also applies to pregnant and lactating women of the same age group.”
Intestinal calcium absorption occurs through both an active, saturable, transcellular process and a non-saturable, passive process. Active transport is controlled by 1,25(OH)2D and passive transport is paracellular. Calcium absorption varies considerably throughout the lifespan, being higher during periods of rapid growth and lower in old age.
Calcium absorption is affected by vitamin D status; it has been shown to be low in patients with vitamin D deficiency, but there is uncertainty about the serum concentration of 25(OH)D that is required for optimal calcium absorption. Unabsorbed dietary calcium is lost in the faeces. The main routes of obligatory (endogenous) calcium loss are urine, faeces, and skin and sweat (dermal losses).
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The NDA opinion can be found here.
An AI is the value estimated when a Population Reference Intake (PRI) cannot be established because an average requirement cannot be determined. An AI is the average observed daily level of intake by a population group (or groups) of apparently healthy people that is assumed to be adequate. More about the differences between AIs and other measures can be found here.