Kim BJ, et al. - In this case-control study, authors analyzed 72 candidates to estimate the impact of kynurenine, a tryptophan metabolite, on human bone metabolism. They observed a correlation between age and bone marrow (BM) kynurenine level. They found 39.7% higher BM kynurenine level in subjects with fragility hip fracture (HF) as compared to those without. The odds ratio per standard deviation increase in BM kynurenine level for fragility HF was 3.80. They noted an inverse association of BM kynurenine level with bone mass at the total femur. They reported a significant association of higher kynurenine concentrations with higher tartrate-resistant acid phosphatase 5b (TRAP5b) and receptor activator of nuclear factor-κB ligand (RANKL) levels, but not with the bone-specific alkaline phosphatase (BSALP) and osteoprotegerin (OPG) levels, in BM plasma.