Serum bone Gla-protein increases following short-term oral administration of active vitamin D3 in the elderly with vitamin D deficiency

Abstract

Serum bone Gla-protein (BGP) is produced by osteoblasts in a vitamin K- dependent process. It is well known that serum BGP levels increase after oral administration of active vitamin D3 in postmenopausal women and patients with chronic renal failure before dialysis. These findings indicate that active vitamin D3 increases the BGP production by osteoblasts. In the present study, a daily oral dose of 2 μg of 1α(OH)D3 was administered to 10 elderly males (age, 75.0 ± 10.9 years) and 8 young males (age, 29.0 ± 3.2 years) to compare the changes in serum BGP levels between the two groups. None of the subjects had severe renal or hepatic dysfunction or abnormalities in calcium (Ca) metabolism. Serum BGP and 1,25(OH)2D levels in both groups were measured before the initial administration, at 24 h and at 1, 2 and 3 weeks after the start of administration. Serum parathyroid hormone (m-PTH), alkaline phosphatase (ALP), Ca and phosphorus levels were also measured in the elderly group. Serum BGP levels before the initial administration were 4.63 ± 1.8 ng/ml in the elderly group and 4.33 ± 0.92 ng/ml in the young group, with no significant difference between the two groups. In both group serum 1,25(OH)2D levels were slightly increased at 24 h after administration. In the elderly group serum BGP levels increased significantly to 11.5 ± 3.0 ng/ml, an increase of approximately 250%, 1 week after the initial administration and the increase was maintanied for up to 3 weeks after the administration commenced. However, no changes in serum BGP levels were noted in the young group. In the elderly group serum m-PTH levels were 544 ± 257 pg/ml, almost the upper normal limit, before, and decreased slightly after, the administration of 1 a(OH)D3. Serum ALP levels also decreased slightly after the administration and serum Ca levels were slightly increased, however, the changes were within normal limits. We conclude that osteoblastic function is activated after short-term administration of active vitamin D3 in vitamin D deficient elderly subjects.