A recent study published in the journal Medicine (Baltimore) has highlighted a significant association between excess body fat and rheumatoid arthritis (RA), suggesting that a newer obesity-related measure known as relative fat mass (RFM) may provide better insight into arthritis risk than the commonly used body mass index (BMI). Increasing evidence has shown that obesity contributes not only to metabolic disorders but also to inflammatory and autoimmune conditions such as RA.
The study analyzed data from the National Health and Nutrition Examination Survey collected between 1999 and 2018 and included 43,499 participants, among whom 2,557 had RA. Researchers used weighted multivariable logistic regression analysis and found that higher RFM levels were independently associated with a greater likelihood of RA. Individuals in the highest RFM category had nearly 2.5 times higher odds of having RA compared with those in the lowest category. Statistical modelling further demonstrated a clear linear relationship between increasing RFM and RA prevalence, indicating that arthritis risk rose progressively with increasing body fat levels.
Researchers also observed that the strength of the association varied across different population groups. Factors such as age, educational status, and smoking significantly modified the relationship between RFM and RA. In addition, RFM demonstrated slightly better predictive performance than BMI in identifying RA risk. However, the ability of both measures to independently predict rheumatoid arthritis remained modest, indicating that they may not yet be suitable as standalone screening tools in routine clinical practice. Supporting findings from earlier international studies have similarly linked higher RFM levels with increased arthritis prevalence, particularly among populations with elevated obesity burden and cardiovascular risk factors.
Experts believe the findings reinforce the growing understanding that excess adipose tissue plays an important role in chronic inflammation and autoimmune disease development. Unlike BMI, which only considers weight relative to height, RFM is designed to estimate body fat percentage more directly and may therefore better reflect obesity-related inflammatory burden. Researchers emphasized that further prospective and mechanistic studies are needed to determine whether reducing body fat can lower RA risk and to clarify the biological pathways linking obesity and autoimmune inflammation. The study also highlights the importance of lifestyle modification, weight management, and smoking cessation as part of long-term strategies aimed at reducing arthritis burden and improving overall health outcomes.
References
- Sun Y, Wu R, Lin Y. Association between relative fat mass and rheumatoid arthritis: A cross-sectional study. Medicine (Baltimore). 2026 Mar 6;105(10):e47822.
- Yang Y, Li Y, Shui R, Li D. Association between relative fat mass and risk of arthritis: a study based on populations in China and the United States. Front Nutr. 2025 Sep 2;12:1555135.