Both very low and very high body mass index (BMI) and body fat are independently associated with greater disease activity and physical dysfunction, but an equal amount of joint damage in patients with established rheumatoid arthritis (RA), UK researchers show.
A high percentage of patients with RA suffer from rheumatoid cachexia, which is characterized by a loss of lean body tissue that is often compensated for by a gain in body fat, explain Antonios Stavropoulos-Kalinoglou (Wolverhampton University, Walsall, West Midlands) and co-investigators.
They add that adipose tissue secretes a number of bioactive proteins including tumor necrosis factor alpha and interleukin-6 that could potentially result in more active disease in obese RA patients.
Stavropoulos-Kalinoglou and team carried out the present study to identify possible associations between weight, BMI and/or body fat with RA disease activity and severity in patients with established disease.
They measured BMI, body fat, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) positivity and disease activity score in 28 joints (DAS28) in 294 volunteers (74% women) with a mean age of 63 years and mean disease duration of 13 years.
Smoking status, physical function by health assessment questionnaire (HAQ), presence of joint erosions and joint surgery were also assessed.
Multiple logistic regression adjusted for age, gender, smoking status, disease duration and RF and anti-CCP positivity, revealed that BMI was significantly associated with ESR and HAQ while body fat was associated with ESR, CRP, and HAQ. In addition body fat showed a tendency for association with DAS28.
In contrast, binary analyses showed that BMI and body fat were not associated with the presence of joint erosions or surgery.
When the patients were grouped according to BMI, the researchers found that underweight and obese patients had significantly worse CRP and physical dysfunction compared with normal-weight patients.
Stavropoulos-Kalinoglou and co-authors comment in the journal Clinical Rheumatology that the cross-sectional nature of the study means that while the associations found are interesting they do not provide definitive evidence for causality or directionality, which can only be addressed in long-term prospective studies.