Obesity alters cortical and trabecular bone density and geometry in women

Abstract

Summary The goal in this study was to determine the relationship between body mass index and trabecular and cortical bone using quantitative computed tomography. A higher body mass index (BMI) was positively associated with trabecular and cortical bone parameters, and serum parathyroid hormone, and negatively associated with cortical volumetric bone mineral density (vBMD) and serum 25-hydroxy-vitamin D. When BMI is greater than 35 kg/m2, adiposity affects vBMD and may explain the higher fracture risk in this population without low BMD. Introduction The influence of adult obesity on the trabecular and cortical bone, geometry, and strength has not been fully addressed. The goal in this study was to determine the relationship between body mass index and trabecular and cortical bone mass and geometry, over a wide range of body weights. Methods We examined 211 women (25–71 years; BMI 18–57 kg/m2) who were classified into three categories of BMI (kg/m2) including normal-weight (BMI<25), overweight and obese-class I (BMI 25–35) and obese-class II–III (BMI>35), and also by menopausal status. Volumetric bone mineral density (mg/cm3), trabecular, and cortical components as well as geometric characteristics at the 4%, 38%, and 66% from the distal tibia were measured by peripheral quantitative computed tomography, and serum was analyzed for parathyroid hormone (PTH) and 25-hydroxy-vitamin D (25OHD). Results Higher BMI was associated with greater values of trabecular bone and cortical BMC and area and PTH (r>0.39, p<0.001), but lower cortical vBMD and 25OHD (r>−0.27, p<0.001). When controlling for lower leg muscle area, fat area was inversely associated with cortical vBMD (r=−0.16, p<0.05). Premenopausal obese women with both higher BMI and PTH had lower cortical vBMD (r<−0.40, p<0.001). While age is a predictor for most bone variables, fat mass explains more variance for vBMD, and lean mass and 25OHD explain greater variance in geometric and strength indices (p<0.05). Conclusions Severe obesity (BMI>35) increases trabecular vBMD and in the presence of a higher PTH is associated with a lower cortical vBMD without compromising bone geometry and strength. Whether or not a lower cortical vBMD in obesity influences fracture risk over time needs to be further explored.

Obesity and fractures

“…Although adiponectin is inversely related to BMI, it appears to be a marker of a disrupted adaptive response in overweight subjects (5,28). In the Health Aging and Body Composition Study, serum levels of adiponectin were significantly higher in overweight women with fractures when compared with overweight women without fractures (36).…”

“…Exaggeration of introversion and extroversion of the ankle and lower leg in obese subjects may be also responsible for a higher prevalence of fractures at these sites. Moreover, increased body weight can also promote an increase in the pressure (stress) in some sites, predisposing to fracture (28).…”

“…This latter action appears to be mediated by a decreased production of serotonin in the hypothalamic neurons (37). Moreover, adipose tissue also produces inflammatory cytokines, such as interleukin 6 (IL6) that may negatively interfere with the balance between bone resorption and formation (5,28).…”

Areal and volumetric bone mineral density and geometry at two levels of protein intake during caloric restriction: A randomized, controlled trial

“…Trabecular bone parameters are reported at the 4% site and cortical bone at the 38% site, as described previously. (19) The coefficient of variation (CV) was less than 1.7%…”

Obesity and its relationship with falls, fracture site and bone mineral density in postmenopausal women

“…There is a study for obese women that report a higher incidence of ankle fractures, but a reduced hip fracture, as the extra fat mass in pelvis and femur protects this area during a fall 32 . The higher incidence of exaggeration of introversion and extroversion of the ankle and lower leg in obese individuals could be the reason for the increased prevalence of fractures at these body parts.…”