Effects of 1,25 dihydroxyvitamin D₃ administration on circadian mineral rhythms in humans

1,25 Dihydroxyvitamin D₃ (1,25(OH)₂D₃) (2.0 μg) was given intramuscularly to 6 healthy adult males. Twenty-four circadian patterns of blood-ionized calcium (Ca²⁺), serum phosphate (P_i), and total calcium (Ca_T) were assessed pre- and posthormone administration. Correlations of mean mineral rhythms with normative models were significant for each mineral pattern on both study days. Mean Ca²⁺ and Ca_T rhythms became weakly correlated after hormone treatment (r=.39). A small but statistically significant increment in the 24 h grand mean Ca²⁺ concentration was observed on the treatment day compared with the baseline day. However, this increment is less than the year-to-year variability in the grand mean mineral concentrations derived from the same subjects studied under baseline conditions previously. These data indicate that acute parenteral administration of near-physiological (2.0 μg) doses of 1,25(OH)₂D₃ appears to have no major effect on circadian mineral pattern shape or mean mineral concentrations.