NNR 2012 –Calcium
Public consultation answer
M.D., Ph.D. in Biochemistry
Independent senior scientist in nutrition
C.E.O. of Minivent AB
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half is bound to albumin. Parathyroid hormone and 1,25(OH)2D are the most important hormones in the regulation of calcium homeostasis. They contribute to maintenance of constant calcium concentration in plasma by regulating the influx and efflux of calcium in intestine, bone and kidney. Maintenance of a constant concentration of ionised calcium is of vital importance and calcium homeostasis is probably the most tightly regulated homeostatic mechanism in the body
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or by an active energy requiring process. The latter is dependent on the action of 1,25-dihydroxyvitamin D3 (1,25(OH)2D), the hormonal form of vitamin D. Calcium absorption
is thus decreased in vitamin D deficiency. This means that we can not increase the uptake of calcium unless we have at least the physiological level of at least 125 nmol/L. See the Public consultation answer on Vitamin D3. The difference between dietary calcium and that
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(Guéguen et al. 2000). The net calcium absorption in infants is reported to range from about 30 % to 60 %, and between 25-40 % in older children, depending on absolute intake (Abrams 2010). The net absorption is relatively high during puberty (found to be about 34 % on an intake of 925 mg/d (5)) and then declines to 25-20 % in adulthood and even lower at advanced age (Guéguen et al. 2000; Schaafsma 1997). This indicates that the amount of net absorption is about 300 mg per day independent of the oral intake.
Calcium is lost from the body via faeces, urine and skin. Non-absorbed calcium is lost with faeces. In adults on intakes of about 1000 mg the loss amounts to about 70 to 80 % of the intake. This indicates that the amount of net absorption is about 300 mg per day independent of the oral intake. An appreciable amount is excretes via faeces as calcium soaps. Loss via skin and sweat is generally small, about 20-50 mg/d (6,7). Under warm conditions or high physical activity the loss may be appreciably greater.
Loss via urine may vary appreciably from person to person, generally between 100 and 400 mg/d in adults, but is relatively constant within individuals even if the intake varies. In the balance study by Malm (1) the urinary loss decreased from 231 to 201 mg/d (not significant) upon reduction of the intake from 940 mg/d to 450 mg/d. This experiment shows that a decrease of calcium intake is independent of the intake as long as the intake is higher than the uptake/urinary excretion and that the level of vitamin D3 is above 125 nmol/L. The calcium balance is very tightly regulated as long as the intake exceeds urinary excretion. The intestinal uptake is limited to 100-400 mg per day and the blood level of calcium is very tightly regulated by a free urinary excretion and a regulated uptake from the primary urine, again with a little help from my friends vitamin D3 derivates  So the intestines regulate the uptake of calcium and serum level is very tightly regulated by the kidneys as any excess is excreted.
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Requirement and recommended intake
The old fashioned physiological, biochemical and endocrinological knowledge shows us that the calcium intake, uptake and excretion is strictly regulated in the body.
By eating more calcium than excreted in the urine and that the level of vitamin D3 is above the physiological level of 125 nmol/L the body will maintain calcium homeostasis.
The minimum intake of 500 mg calcium applies to all ages and sexes and is then ample for most individuals as long as the level of vitamin D3 is above the physiological level of 125 nmol/L.
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Reasoning behind the recommendation
The recommendations for calcium are maintained and can be decreased in NNR 2012 since no strong scientific evidence to change has emerged. This is under the condition that the level of vitamin D3 is above the physiological level of 125 nmol/L.