Background In general population,a high body mass index,is considered protective against osteoporosis.The relationship of body composition and abdominal adiposity with bone mineral density (BMD) in rheumatoid arthritis (RA) has not been explored.
Objectives To study if body composition and abdominal adiposity are related to BMD in RA.
Methods 197 women (100 RA, 97 controls) adjusted for age and comorbidity were recruited. We determine: body mass index, waist circumference, bone mass by DEXA of the hip, lumbar spine, total body; lean and fat mass according to specific rates and locations; sarcopenia patterns, levels of vitamin D and osteoprotegerin, as well as abdominal fat by MRI, in both groups. Multivariate analysis was performed to study the relationship between bone mass and patterns of body composition and with abdominal adiposity.
Results RA patients showed lower levels of lumbar bone values (βcoef. gr/cm2 -64 [95% CI -122 to 6], p=0.03) and a lower percentage of total body bone mass (βcoef -0.3% [95% CI, 0.5 to 0.1], p=0.01) after adjustment for age and comorbidity. Although values tended to be lower in RA in other areas such as femoral neck, total hip, Ward's triangle or femoral shaft, these differences were not statistically significant. Patients tended to have higher frequency of obesity as BMI>30 kg/m2 (43% vs. 31%, p=0.09), although the analysis of body compartments, fat and lean mass rates, as well as abdominal adiposity, showed no difference between patients and controls. Fat and lean masses were associated,in a positive way, with the levels of BMD at all sites in both groups (total hip β coef. Tscore 1.15 [95% CI 0.08- 0.24], p=0.00 in RA and β coef T score 0.16 [95% CI 0.07-0.24], p=0.00) in controls, after adjusting for age, comorbidity, and vitamin D levels and osteoprotegerin. The values of parietal abdominal adiposity showed a positive relationship with the values of total hip T score in both controls (0.04 T score β coef. [95% CI 0.01 to 0.07], p=0.01) and patients (0.05 T β coef. score [95% CI 0.02-0.07], p=0.00).This relationship was not found with the values of visceral abdominal adiposity. The presence of sarcopenia phenotype tended to be higher in patients (OR 2.95 [95% CI 0.93 to 9.29], p=0.06]. This sarcopenia was associated with lower BMD at the total hip (β coef. T score -1.90 [95% CI, 3.61-0.20], p=0.03) after adjustment for disease activity scores, age, ESR, CRP, rheumatoid factor and vitamin D and osteoprotegerin levels. In contrast, the presence of sarcopenia had no influence on bone mass in controls. Similarly, the combination of obesity and sarcopenia (sarcopenic obesity) showed no association with bone mass in either groups.
Conclusions The protective role of fat and lean mass on BMD is preserved in patients. The pattern of sarcopenia, after adjusting for disease activity was associated with low bone mass in RA. This suggests an independent role of this sarcopenia on bone density in RA, but not in healthy subjects.
Disclosure of Interest None declared