Avaliação da massa óssea em indivíduos obesos mórbidos

Abstract

Recent studies suggest that body fat may not exert a beneficial effect on bone mass in heterogeneus populations. However, little is known about this effect in morbidly obese individuals. Some of the proposed mechanisms to explain the potential negative effect of fat on bone mass support the hypothesis that morbidly obese individuals are particularly susceptible to bone loss. The scarce of information in this group may be, at least in part, explained by methodological limitations due to the use of the first generation of dual energy X ray absorptiometry(DXA) equipment. In the present study, we used a recent DXA equipment that is able to assess individuals with higher body area and total body mass, allowing a more adequate evaluation. The aim of this study was to evaluate bone health of morbidly obese individuals grouped by sex and physiologic period. Seventy-two morbidly obese (BMI>40Kg/cm2) individuals participated in the study and were divided into 3 groups: premenopausal women (n=37), postmenopausal women (n=22) and men (n=13). Body composition and bone area, mineral content (BMC) and mineral density (BMD) of total body and specific sites (lumbar spine, proximal femur and forearm) were evaluated by DXA (LUNAR- iDXA). Anthropometric and biochemical measurements were also assessed. Comparisons between groups were conducted using one way analisis of variance (ANOVA) followed by Fischer´s post hoc test. Associations among variables were evaluated by Pearson´s correlation analysis and by partial correlation. Significance level of 95% was adopted. Mean T- and Z- score values were adequate in all evaluated bone sites. As frequently observed in general population, men had higher BMC and higher bone area (P<0.001) than pre and postmenopausal women in all evaluated sites. However, men had lower Z- scores at lumbar spine, total femur and forearm (P<0.05) compared to both female groups. Contrary to our expectation, no significant differences in any evaluated bone parameter was observed between pre and post menopausal women. Mean serum concentrations of 25-hydroxivitamin D [25(OH)D], parathormone (PTH), osteocalcin(OC), and carboxiterminal telopeptide of type 1 collagen (CTx) were adequate with no significantly different between groups. Considering all 3 groups together, several bone parameters were found to be positively correlated (r>0.30, P<0.05) with total body fat. After adjusting for total body mass (partial correlation), total body fat (kg) was negatively correlated with bone area at total body (P<0.001; r=-0.51), lumbar spine (P<0.01; r=-0,40) and total femur (P<0.001; r=-0.57), and also negatively correlated with BMC at total body (P<0.001; r=-0.51) and total femur (P<0.001; r=-0.47). When groups were evaluated separately, negative associations between fat mass (kg) and total femur bone area, CMO and BMD (r<-0.47; P<0.05) were observed only in the group of postmenopausal women. Our results suggest that, after adjusting for the effect of total body mass, body fat appears to exert a negative influence on bone mass, especially in postmenopausal women. However, as no evidence of inadequate bone mass was observed in the studied individuals, it is possible that the beneficial mechanical effect of total body mass on bone mass has been able to overcome the detrimental effect of fat on bone