Different effects of oral conjugated equine estrogens and transdermal estrogen on undercarboxylated osteocalcin concentration in postmenopausal women

Vitamin D supplementation and bone turnover in advanced heart failure: the EVITA trial

Low vitamin D status is common in patients with heart failure and may influence bone health. A daily vitamin D dose of 4000 IU (moderately high dose) for 3 years had however no effect on parameters of bone metabolism, even in patients with very low vitamin D status.

INTRODUCTION

Low vitamin D status is common in patients with heart failure (HF) and has been related to disturbed bone turnover. The present study investigated the effect of a daily vitamin D₃ dose of 4000 IU on bone turnover markers (BTMs) in patients with advanced HF and 25-hydroxyvitamin D (25OHD) concentrations < 75 nmol/L.

METHODS

In this pre-specified secondary analysis of a randomized controlled trial, we assessed in 158 male HF patients (vitamin D group: n = 80; placebo group: n = 78) between-group differences in calciotropic hormones (25OHD, 1,25-dihydroxyvitamin D [1,25(OH)₂D], intact parathyroid hormone [iPTH]), and BTMs (cross-linked C-telopeptide of type I collagen, bone-specific alkaline phosphatase, undercarboxylated osteocalcin). Comparisons were performed at the end of a 3-year vitamin D supplementation period with adjustments for baseline values.

RESULTS

Compared with placebo, vitamin D increased 25OHD on average by 54.3 nmol/L. At study termination, 25OHD and 1,25(OH)₂D were significantly higher (P < 0.001 and P = 0.007, respectively), whereas iPTH tended to be lower in the vitamin D group than in the placebo group (P = 0.083). BTMs were initially within their reference ranges and did not differ significantly between groups at study termination, neither in the entire study cohort nor when data analysis was restricted to the subgroup of patients with initial 25OHD concentrations < 30 nmol/L (n = 54) or to patients with initial hyperparathyroidism (n = 65) (all P values > 0.05).

CONCLUSIONS

A daily vitamin D₃ dose of 4000 IU did not influence BTMs. Data indicate that vitamin D supplementation will not lower bone turnover in male patients with heart failure.

An old friend in a new light: the role of osteocalcin in energy metabolism

Accumulating evidence suggests interactions between bone and energy metabolism, which may affect the risk of cardiovascular disease. Recent animal studies indicate that osteocalcin (OC) plays a key role in the coordinated regulation of glucose and insulin metabolism while insulin receptors on osteoblasts may regulate bone turnover and circulating OC levels. Association studies, weight loss interventions, and observational data lend some support to the existence and relevance of these mechanisms in humans. However, corroborating evidence from pharmacologic interventions in either bone or glucose metabolism is limited by the number, design, and complex pharmacological effects of the drugs used. Furthermore, such clinical trials are complicated by the alteration of metabolic feedback mechanisms in the insulin resistant state. Purpose-designed studies are needed to further establish the existence and significance of the role of OC and its subfractions in human insulin metabolism. In this review we summarize existing animal evidence regarding the role of OC and its subfractions in bone and energy metabolism and assess current clinical trial evidence relating to the significance and consequences of this relationship in humans.

Bone and glucose metabolism: a two-way street

Evidence from rodent models indicates that undercarboxylated osteocalcin (ucOC), a product of osteoblasts, is a hormone affecting insulin production by the pancreas and insulin sensitivity in peripheral tissues, at least in part through enhanced secretion of adiponectin from adipocytes. Clinical research to test whether this relationship is found in humans is just beginning to emerge. Cross-sectional studies confirm associations between total osteocalcin (OC), ucOC and glucose metabolism but cannot distinguish causality. To date, longitudinal studies have not provided a consistent picture of the effects of ucOC or OC on fasting glucose and insulin sensitivity. Further exploration into the physiological and mechanistic effects of ucOC and OC, in rodent models and clinical studies, is necessary to determine to what extent the skeleton regulates energy metabolism in humans.

Roles for vitamin K beyond coagulation

Recent interest in vitamin K has been motivated by evidence of physiological roles beyond that of coagulation. Vitamin K and vitamin K-dependent (VKD) proteins may be involved in regulation of calcification, energy metabolism, and inflammation. However, the evidence for many of these proposed roles in the maintenance of health is equivocal. There is also an emerging viewpoint that the biochemical function of vitamin K may extend beyond that of a cofactor for the VKD carboxylation of glutamyl residues (Glus) to carboxylated Glus in VKD proteins.