| Objective To explore the associations of body mass index (BMI), fat mass index (FMI), skeletal muscle mass index (SMI) and secondary osteoporosis (OP) in patients with rheumatoid arthritis (RA). Methods Four hundred and eighty patients with RA and 158 normal controls were enrolled. Bone mineral density (BMD) at sites of femur neck (Neck), greater trochanter (G.T), total hip (Hip) and lumbar vertebrae 1-4 (L1, L2, L3, L4) was measured by dual energy X-ray absorptiometry and OP was diagnosed according to the criteria of OP. Skeletal muscle mass, percentage of body fat and mineral content were measured by biological electrical impedance, and BMI, FMI and SMI were calculated. Results RA patients had significantly lower BMD at each site measured than normal controls (P<0.0001), and had significantly higher incidence of OP (42.6%, 178/418) than the control group (13.9%) (?2=41.551, P<0.0001). Incidence of sarcopenia in RA patients was 54.5%, which was significantly higher than that in the control group (9.0%) (?2=96.747, P<0.0001). BMD, SMI, FMI, mineral content, percentage of body fat, skeletal muscle mass and muscle mass of both upper and lower limbs in RA patients among different BMI groups were significantly different (P<0.0001), and there were linear increasing tendencies with increased BMI (P<0.0001). In RA patients with BMI<18.5 kg/m2, incidence of OP in RA patients with sarcopenia was similar to those without sarcopenia (48.1% vs 45.5%, ?2=0.027, P=0.870). In RA patients with normal BMI, or were overweight or obese, incidences of OP in RA patients with sarcopenia was significantly higher than that in RA patients without sarcopenia (56.6% vs 33.0%, ?2=12.238, P<0.0001; 52.6% vs 22.7%, ?2=10.953). In RA patients with or without sarcopenia, there were no significant differences regarding the incidence of OP among different BMI groups (P=0.563, 0.148). Linear correlation analysis showed that there were positive linear correlations between SMI and BMD of each site measured and BMI (P<0.0001), but there was a negative linear correlation between SMI and percentage of body fat (P<0.0001). Logistic regression analysis found that SMI (OR=0.696, P=0.001, 95%CI: 0.565-0.857) was a protective factor for OP in RA, and age (OR=1.091, P<0.0001, 95% CI: 1.065-1.117) and sex (OR=5.259, P<0.0001, 95%CI: 2.543-10.876) were risk factors. Conclusion BMI, SMI and FMI are associated with the occurrence of OP in RA patients, SMI rather than BMI was the most important protective factor for OP in RA. |