The Relationship of Serum Serotonin Levels to the Rate of Bone Loss and Fractures in Men

Recent genetic studies in rodents have revealed that circulating serotonin plays a key role in regulating bone formation and skeletal mass. However, the reported effects of circulating serotonin on bone mass in humans have been conflicting. We determined whether circulating serotonin levels influenced the rate of bone loss and fractures in men. We assessed the effect of serum serotonin on bone loss rate in a population-based cohort of 202 ambulatory men aged 56-70 years who were followed up for a median duration of 3.7 years. Serum serotonin levels were assayed, and the Timed Up and Go Test (TUGT) was performed, at baseline. Dual-energy X-ray absorptiometry was performed both at baseline and during follow-up. Fracture prevalence was assessed using questionnaires. The serotonin levels were inversely associated with the lumbar spine bone mineral density (r = −0.174, p = 0.028) at baseline. No association was evident between the bone mineral densities of the femoral neck or total hip and serotonin level. The annual rates of bone loss from the lumbar spine, the femoral neck, and the total hip were 0.01%, 0.46%, and 0.46%, respectively. The baseline serum serotonin level did not predict the bone loss rate in any skeletal site. Lower limb disability evident upon TUGT at baseline predicted bone loss from the total hip. No significant difference of serotonin level was observed between subjects with and without fractures. The serum serotonin level was not associated with the rate of bone loss in elderly men. Thus, the circulating serotonin level does not reliably predict bone loss.