Metformin, is a first line oral antidiabetic drug that improves cellular insulin sensitivity in insulin resistant individuals, especially those with type 2 diabetes. There is substantial evidence to suggest that metformin has a beneficial effects on maintenance of bone metabolism [
10,
11]. It has been shown that metformin has a positive effect on BMD in preclinical studies [
5]. Metformin affects glucose metabolism through activation of AMP-activated protein kinase (AMPK). AMPK is expressed in bone cells and has subunits differentiated for expression and activation. AMPK α1 is expressed in primary osteoblasts, primary bone marrow macrophages, osteoclasts and other bone cell lines [
12]. Metformin affects the differentiation and mineralization of osteoblastic MC3T3-E1 cells through AMPK and nitric oxide synthesis and production of bone morphogenetic protein-2 [
13]. In another study, Cortizo et al. showed an effect of metformin on the differentiation of osteoblastic cell lineages (MC3T3-E1 and UMR106), in addition to increased levels of bone formation markers such as alkaline phosphatase [
14]. What is more, metformin has the ability to prevent AGE-induced changes, i.e. induction of apoptosis, caspase-3 activity, reduction of RAGE activity, changes also involved in the reduction of intracellular oxidative stress. Although the direct mechanisms of metformin signalling are not fully understood, data indicate AGE-RAGE interaction in modulating osteoblastic cell growth and differentiation [
15]. In addition, metformin has an osteogenic effect, which is due to an increase in the osteoblast-specific transcription factor Runx2/Cbfa [
16]. Thus, evidence suggests that metformin has a direct effect on inhibiting bone loss. A population-based cohort study conducted in South Korea found no association between bone fracture risk and metformin use in patients with T2DM. Oh T. et al. also showed no clinical benefit in terms of bone fracture risk in patients with T2DM [
17]. In contrast, Vestgard et al. showed a reduced risk of bone fractures [
18]. In addition, subsequent studies, including two meta-analyses, have shown that metformin use was associated with a reduced risk of total bone fractures among patients with diabetes. The discrepancy between those observations may be due to differences in considered populations, experimental methods, concentrations and duration of treatment with metformin. Thus, current evidence that metformin therapy reduces fracture risk is lacking [
19]. Therefore, further studies are needed to investigate possible beneficial effects of metformin on bone metabolism to obtain a clinical consensus.