The impact of obesity through fat depots and adipokines on bone homeostasis
Obesity and osteoporosis are two of the most common chronic disorders with high prevalence rates, and the literature reports contradictory results when considering the relationship between body mass index (BMI)/obesity and bone metabolism. Although several arguments support a key role played by the adipose tissue in this process, the exact mechanism remains poorly understood. First, the pattern of regional fat deposition into the subcutaneous and visceral compartments is suggested as a stronger predictor of osteoporosis risk than overall fat mass. Second, fat deposited in the bone marrow influences osteoblast differentiation and function, increases osteoclastic activity that in turn affects mineralization. Third, adipose tissue is a highly dynamic organ, secreting various adipokines with endocrine and metabolic roles, regulating bone homeostasis. Altogether these arguments support that abnormal local fat deposition and adipose tissue secretions are key factors in the interaction between obesity and impaired bone metabolism. In this review, we examine the interaction between fat and bone health from two perspectives: (I) the different deposition of adipose tissue [subcutaneous, visceral and marrow adipose tissue (MAT)] and (II) the influence of adipokines in bone metabolism.