Patients with rheumatoid arthritis exhibited increased body fat for a given body mass index when compared with healthy controls in a recent study. This suggests that standard BMI cut-off points in those patients with rheumatoid arthritis should be reduced to more accurately reflect risk for cardiovascular disease, according to Dr. Antonios Stavropoulos-Kalinoglou of the University of Wolverhampton's Research Institute in Healthcare Science, England, and his associates.
BMI does not distinguish between fat and lean body mass when it uses height and weight to measure body mass. As a result, individuals with the same height and weight, but different muscle content, may have the same BMI but different levels of body fat. This shortcoming should be taken into consideration when determining risk for cardiovascular disease, especially with rheumatoid arthritis (RA) patients, who often experience involuntary loss of lean body mass and an increase of fat mass, according to the researchers (Ann Rheum Dis. 2007 Feb. 8 [Epub doi:10.1136/ ard.2006.060319]).
The study included 299 individuals: 174 with RA, 43 with osteoarthritis of the hip or knee, and 82 healthy, medication-free controls by self-report. Body fat was assessed in all participants by bioelectrical impedance using a body analyzer. BMI was calculated based on measured height and weight.
Body fat and BMI differed significantly between those with RA and healthy controls, judging from analyses of covariance findings. For a given BMI, patients with RA showed significantly increased levels of body fat percentage compared with the healthy participants. Patients with RA also showed BMI levels reduced by 1.83 kg/m
The study also found that when the widely accepted BMI cut-offs of 25 kg/m
These misclassifications were corrected when the proposed rheumatoid arthritis-specific BMI cut-offs of 23 kg/m
However, body fat percentage is a better way to assess fat measurement and risk for cardiovascular disease, according to the investigators. They developed a predictive model as part of the study to calculate body fat of RA patients without relying on the sophisticated equipment often needed to measure body fat.
The model, which uses BMI, age, gender, and disease status to determine body fat, was validated using Limits of Agreement Analysis against measured body fat in a group of 342 patients with RA. In that validation group, the model predicted body fat to be 0.4% higher than actual levels, but results were within suitable limits and the cross-validation was “reassuring,” according to the investigators.