by David Douglas

Last Updated: 2007-10-23 18:52:22 -0400 (Reuters Health)

NEW YORK (Reuters Health) – The relationship of a given body mass index (BMI) value to body composition in patients with rheumatoid arthritis (RA) differs from that of patients with osteoarthritis (OA) and healthy controls, according to UK researchers.

"Patients with RA may have more fat in their bodies — and experience the adverse health effects of fatness — with weight and BMI that are not traditionally associated with obesity in the general population," senior investigator Dr. George D. Kitas told Reuters Health. "This is important for the management of individual patients with rheumatoid arthritis."

Dr. Kitas of the Dudley Group of Hospitals NHS Trust and colleagues studied 174 RA patients, 43 OA patients and 82 healthy controls. A further 324 RA patients served as a validation group. The findings appear in the October 1st issue of the Annals of the Rheumatic Diseases.

The team found that significant BMI differences among groups were mainly due to age. However, for a given body fat content, RA and OA patients showed lower BMI levels than did controls. This difference was significant only in RA patients.

The researchers calculated that in RA patients, BMI values and hence cut-off points should be reduced by 2. This yields a threshold of 23 for being overweight and 28 for obesity.

The equation that was developed, say the investigators, was able to accurately establish body fat level from the BMI in patients with RA.

"The contribution of fatness to the increased risk for cardiovascular disease in patients with RA needs to be re-assessed," continued Dr. Kitas. At this stage, this is not "directly relevant to individual patients, but is important for further epidemiological research of the link between RA and cardiovascular disease."

Ann Rheum Dis 2007;66:1316-1321.