Effect of calcium intake on serum levels of 25‐hydroxyvitamin D3

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Abstract
The effects of high calcium intake on vitamin D metabolism were investigated. To the normal diet of 14 healthy men, 2 g calcium were added daily for 6–7 weeks. The mean serum concentration of 25‐hydroxyvitamin D3 increased from 73 ± 7 to 94 ± 6 nmol l‐1 (Pt‐test; Pt‐test) in the subjects receiving calcium, whereas there was only a minimal increase, from 67 ± 5 to 71 ± 4 nmol l‐1 in a control group on a normal diet. At the end of the study the difference between the test group and the controls was highly significant (P<0·005). The calcium loading caused a statistically significant depression of the serum levels of 1,25‐dihydroxyvitamin D. The results obtained are in agreement with previous studies in rats and indicate that calcium intake is of some importance for the serum level of 25‐hydroxyvitamin D3. The findings are discussed in relation to our previous finding that there is a relationship between high 25‐hydroxyvitamin D3 levels and hypercalciuria in renal‐stone formers.