Obesity, vitamin D status and physical activity: 1,25(OH)2D as a potential marker of vitamin D deficiency in obese subjects.

BACKGROUND: Obesity has been regarded to be protective against fracture in spite of its association with low levels of vitamin D. Vitamin D is the key regulator of bone metabolism and its deficiency contributes to higher level of parathyroid hormone (PTH), leading to the activation of bone turnover. METHODS: We studied 161 subjects of which 65 were young healthy subjects and 96 were elderly subjects. We measured creatinine, 25(OH)D, 1,25(OH)2D, PTH, albumin, and calcium plasma levels, we evaluated physical activity, and we calculated BMI. A sub-cohort of elderly subjects also underwent DXA scans. RESULTS: Overweight and obese subjects, as well as underweight ones, had lower levels of vitamin D but normal serum concentrations of 1,25(OH)2D and PTH was higher in underweight and obese subjects. Moreover, we found a nonlinear relationship between body mass index (BMI) and PTH with a significant U-shaped exponential regression. Regardless of BMI, 25(OH)D mean levels were higher in subjects who practice physical activity. CONCLUSIONS: These findings suggest that physical activity and BMI had a significant effect on the metabolism of bone and vitamin D, but the effect of BMI was different in underweight, normal weight or obese subjects. In obesity the real vitamin D deficiency could be estimate by serum 1,25(OH)2D concentrations whose lower levels contribute to the higher PTH production and consequently to bone loss and to a greater fracture risk.

Osteoprotegerin in diabetic osteopathy.

AIM: The aim of this study is to evaluate the relationship between OPG and the degree of glycaemic control in a population of elderly subjects. METHODS AND RESULTS: Data presented included 172 elderly subjects, of whom 107 were hospitalized for a hip fracture and 65 were non fractured outpatients. All participants received a multidimensional geriatric evaluation and underwent blood sampling. HbA1c, OPG, CTX and OC were measured and DXA scans were performed. Carotid intima-media thickness (IMT) was measured in all outpatients. Diabetic patients had more comorbidities, higher mean values of lumbar spine and femoral neck BMD and T-score, lower circulating levels of OC and CTX, and higher circulating levels of OPG compared to non-diabetic subjects. OPG was directly correlated with HbA1c. This association was most evident in non-fractured elderly subjects. Moreover, diabetic patients with IMT>1.5 mm had greater mean values of OPG than non-diabetic subjects with high IMT and than elderly subjects with IMT < 1.5 mm, with and without T2DM. CONCLUSIONS: Diabetic patients have reduced circulating levels of OC and CTX, and elevated serum levels of OPG, suggesting a state of low bone turnover. Reduced bone turnover causes an increase of BMD and could lead to a poor bone quality. OPG and HbA1c were directly correlated and OPG mean values were higher in diabetic patients with poor glucose control. Diabetic osteopathy could be considered a late complication of T2DM, directly related with the degree of glucose control and the duration of the disease.