As the Australian population ages, the prevalence of age-associated comorbidities including osteoporosis, diabetes and cardiovascular disease increases. Diabetes is associated with increased fracture risk but the mechanisms underlying this relationship remain unclear. Undercarboxylated osteocalcin (ucOC) is bone-derived peptide present in the circulation which was identified by the Karsenty laboratory in 2007 as a modulator of insulin secretion and sensitivity in mice, linking bone metabolism with diabetes risk. To test whether or not ucOC plays a similar role in humans, ucOC, total osteocalcin, and the distinct bone turnover markers N-terminal propeptide of type I collagen (P1NP) and collagen type I C-terminal cross-linked telopeptide (CTX) were assayed 4,248 community-dwelling men aged 70-89 years in the Western Australian Health In Men Study (HIMS). Bone turnover markers were assayed in serum using immunoassay; ucOC after hydroxyapatite binding and precipitation of carboxylated osteocalcin. Reference ranges for ucOC, total osteocalcin, P1NP and CTX were determined to guide the assessment of osteoporosis and fracture risk in older men. As a group, men with diabetes had lower ucOC, total osteocalcin, P1NP and CTX compared with non-diabetic men. Higher ucOC was an independent predictor of reduced diabetes risk; distinct from associations with other bone turnover markers. In multivariate analysis adjusting for age, smoking, BMI, conventional cardiovascular risk factors, creatinine, vitamin D and medical comorbidity, a 1-SD increase in ucOC was associated with odds ratio for diabetes of 0.56 (95% confidence interval 0.44-0.72) independently of other bone turnover markers. Furthermore a higher proportion of ucOC relative to total osteocalcin in the circulation was an independent predictor for lower risk of myocardial infarction men. These findings provide fresh insights into the manner in which bone turnover, diabetes and cardiovascular disease are inter-related, opening up new possibilities for health promotion in older adults.