Women with rheumatoid arthritis (RA) who are obese have significantly higher C-reactive protein (CRP) levels and slightly elevated erythrocyte sedimentation rate (ESR) when compared with women with RA without obesity and women in the general population, but this relationship is not related to RA disease activity, according to recent research published in Arthritis Care & Research.
“[O]besity was associated with greater CRP in women with RA, independent of other components of disease activity,” Michael George, MD, MSCE, from the Division of Rheumatology at the University of Pennsylvania in Philadelphia, and colleagues wrote in their study. “A similar association was observed in a non-RA sample, suggesting that elevated CRP values among obese women with RA are not reflective of greater RA disease activity but rather are an expected phenomenon related to adiposity. In contrast to associations observed in women, low [body mass index (BMI)] and not obesity was associated with greater CRP in men with RA.”
Dr George and colleagues analyzed the relationship among BMI, CRP, and ESR in 451 patients in the cross-sectional Body Composition (BC) cohort and 1652 patients in the longitudinal Veterans Affairs Rheumatoid Arthritis (VARA) registry. Patients in the BC cohort underwent full-body dual-energy x-ray absorptiometry measures of fat mass index, whereas data from patients in the VARA registry underwent a multivariate analysis stratified by sex. The researchers used patient data from the National Health and Nutrition Examination Survey as a control group.
The authors found that women with RA in the study who were obese had a higher CRP linked to their BMI, and patients with BMI ≥35 kg/m2 showed the greatest increase in CRP when compared with patients who had a BMI between 20 and 25 kg/m2 (P <.001).
The researchers found a significant association between greater BMI and elevated CRP after adjusting for joint counts and patient global scores in the BC (P <.001) and VARA (P <.01) groups, but there was no significant association after adjusting for fat mass (P =.17). The investigators noted a positive association between BMI and ESR for women in both groups, but severely obese women in the BC group had a significantly higher ESR level when compared with women at a normal BMI.
For men with RA, the researchers found that men with a lower BMI had higher ESR and CRP rates when compared with men who were obese or severely obese.
“The evidence from the current study suggests that this inverse association between BMI and CRP in men is a RA-specific phenomenon and not a direct causal effect of adiposity — the positive association between BMI and CRP in the general population suggests that adiposity can contribute to greater CRP levels in men as well as women,” Dr George and colleagues wrote.
Summary & Clinical Applicability
“[O]besity is associated with greater CRP in women with RA, similar to what is seen in the general population,” Dr George and colleagues wrote. “This association is explained by greater fat mass and not greater RA disease activity, suggesting that CRP should be interpreted cautiously among women with obesity. Higher CRP levels are observed among low and normal weight men with RA and may reflect greater systemic inflammation related to RA or other comorbid conditions in this group.”
The researchers noted limited power to study the effects of factors such as BMI, disease activity, and ESR, and dual-energy x-ray absorptiometry measures of fat mass were only available in the BC group.
Dr Michaud received research grants from Pfizer. Dr Ogdie-Beatty is a paid consultant for Novartis and Pfizer and received grants from Pfizer. Dr Sauer received grants from Amgen.
George MD, Giles JT, Katz PP, et al. The impact of obesity and adiposity on inflammatory markers in patients with rheumatoid arthritis [published online April 10, 2017]. Arthritis Care Res. doi: 10.1002/acr.23229