Bone quality and vitamin K2 in type 2 diabetes: review of preclinical and clinical studies.

Type 2 diabetic patients are at high risk of bone fractures even if their bone mineral density is normal or high. This is likely explained by poor bone quality and extraskeletal factors. The present review was conducted to provide an overview of the currently available preclinical and clinical evidence on the effect of vitamin K(2) on bone quality in persons with type 2 diabetes. Vitamin K(2) stimulates γ-carboxylation of osteocalcin and can increase bone formation through steroid and xenobiotic receptors. Clinical studies of type 2 diabetic patients have shown detrimental collagen cross-links in bone; low serum insulin-like growth factor-I and osteocalcin concentration are associated with an increased risk of fractures. A therapeutic strategy for preventing fractures in type 2 diabetic patients remains to be established. One recent preclinical study showed that vitamin K(2) administration in a type 2 diabetic rat model had the following skeletal benefits: increased serum osteocalcin, improved collagen cross-link profiles, and increased bone strength. These new findings suggesting a possible beneficial effect of vitamin K(2) supplementation on bone quality in type 2 diabetes warrant further investigation.