Competing interests

Background—It has been known for more than 70 years that citrate is a major component of bone; comprising 1–2 % weight of bone, and a concentration that is ~5–25-fold greater than the citrate concentration of most other tissues. This relationship exists in humans and in all vertebrates; which reveals that it is an indispensible and essential structural/functional component of bone. However, its implications relating to the structure and properties of bone, to the process of bone formation and regeneration, to bone disorders, and other issues have remained largely unknown and unaddressed. Recent studies have identified citrate as a structural component of the apatite nanocrystal/collagen complex, which is essential for imparting the bone properties of stability, strength, and resistance to fracture. This raises the issues of the status of citrate, and its source in normal bone formation. © 2014 Costello et al; licensee Herbert Publications Ltd. This is an Open Access article distributed under the terms of Creative Commons Attribution Licens