No change in calcium absorption in adult Pakistani population before and after vitamin D administration using strontium as surrogate.

UNLABELLED: Vitamin D, parathyroid hormone levels and calcium absorption was assessed before and after cholecalciferol using Strontium as a surrogate. Increase in 25OHD, lowering of iPTH with no effect on Sr absorption was seen, suggesting the possibility that maximal Ca absorption had already been achieved in these volunteers.

INTRODUCTION: This paper discusses the determination of calcium (Ca) absorption, using strontium (Sr) as a surrogate, before and after a single IM injection of vitamin D(3) (600,000 IU).

METHODS: Baseline serum 25-hydroxyvitamin D (25OHD), Sr, Ca, P, and intact parathyroid hormone (iPTH) were determined in 53 fasting volunteers, followed by administrating (PO) 0.03 mM (4.8 mg/kg) SrCl(2) and collecting blood at 0.5, 1 and 4 h to determine the absorption (AUC(0 → t )) of Sr. Following the initial absorption test, volunteers received a single IM injection of 600,000 IU vitamin D(3). Two months later, the fasting serum and the Sr absorption test were repeated, as described above.

RESULTS: The IM injection of vitamin D(3) caused a significant increase in fasting 25OHD (from 43.5 ± 19 to 66.1 ± 19.1 nmol/L (p < 0.001)) and a trend toward lower serum iPTH (from 59.8 ± 27.8 to 53 ± 31 ng/L). Fasting serum Ca and P remained unchanged. A higher 25OHD level failed (p = 0.32) to translate into a higher rate of Sr absorption. AUC(0 → 4 h) were almost identical before and after the IM injection of vitamin D(3).

CONCLUSION: A single vitamin D(3) injection of 600,000 IU significantly increase mean 25OHD concentration and tended to lower iPTH concentrations in volunteers with initially low 25OHD status, suggesting to utilize this simple form of treatment to improve vitamin D status and to have a possible biological effect on Ca homeostasis. However, we found no obvious effect on Sr absorption, suggesting the possibility that maximal vitamin D-dependent Ca absorption had already been achieved in these volunteers at a lower vitamin D status.