High body mass index (BMI) was associated with greater levels of the rheumatoid arthritis (RA) biomarkers C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) in women with and without RA.
“The increase in these levels of inflammation was not because rheumatoid arthritis was worse in these women,” said Dr Michael George of the University of Pennsylvania Health System.
In fact, we found that obesity leads to very similar increases in these lab tests even in women without rheumatoid arthritis.”
Meanwhile, low BMI was associated with a greater levels of CRP and ESR in men with RA.
Dr George believed that RA and obesity could both contribute to levels of inflammation, making the diagnosis of lab tests more complicated.
The findings also raise questions about the relationship between weight and inflammation and how it may differ between men and women.
“Physicians might assume that high levels of inflammation mean that a patient has rheumatoid arthritis or that their rheumatoid arthritis requires more treatment when in fact a mild increase in levels of inflammation could be due to obesity instead,” he explained.
In the study, BMI associations with CRP and ESR were investigated in two RA sample groups.
One measured the cross-sectional Body Composition (BC) and included whole body measures of fat mass index of 451 men and women aged between 18-70 years.
The other group, known as the VA Rheumatoid Arthritis (VARA) Registry Cohort, consisted of 1,652 males and females over the age of 18.
Follow-up visits included the questionnaires that asked about swollen and tender joint counts, inflammatory markers, pain scores, and patient and physician disease assessment scores.
The team found among women with RA and in the general population, greater BMI was associated with greater CRP, especially among women with severe obesity.
Positive associations between BMI and ESR in women were more modest. In men with RA lower BMI was associated with greater CRP and ESR, contrasting positive associations among men in the general population.
“In this study, obesity was associated with greater CRP in women with RA, independent of other components of disease activity,” the study stated.
“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.”
Inflammation and weight
Inflammation has already been shown to have different effects on body composition in men and women.
This could explain why different associations were seen among men and women with RA.
While a lower BMI was associated with a greater swollen joint count among men with RA, differences in joint counts and patient global scores alone could not explain the higher CRP and ESR in men with lower BMI.
“Furthermore, because obesity may be expected to impact the reliability of other component measures of disease activity, clinicians may tend to rely more on objective measures such as CRP for diagnosis or to make treatment decisions,” the study concluded.
Source: Arthritis Care & Research
Published online ahead of print: DOI 10.1002/acr.23229
“The impact of obesity and adiposity on inflammatory markers in patients with rheumatoid arthritis.”
Authors: Michael George et al.