• Calcium 1,25-dihydroxyvitamin D;
  • human;
  • 25-hydroxyvitamin D3;
  • rat

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 (P<0·05, Student's unpaired t-test; P<0·01, paired t-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.