Obesity is paradoxically associated with a lower risk of mortality in chronic illnesses including rheumatoid arthritis (RA). Weight loss in patients with poor health, however, may in part explain this observation. This study evaluated the impact of weight early in life and weight loss on mortality in patients with RA.
Patients with RA (age >40 years) were active participants in a prospective clinical registry with up to 17 years of follow-up. Current and age-30 body mass index (BMI) were determined from self-report of height and weight from semi-annual questionnaires. Mortality was assessed from National Death Index. Risks of obesity reported from both early in life and at enrolment in the registry were evaluated using Cox proportional hazards models.
Among 12,679 participants (80% female), there were 1,520 deaths in 80,502 person-years. Obesity at enrolment (BMI >30 kg/m2) was modestly associated with greater mortality [HR: 1.34 (1.18,1.53) p=0.001]. Adjusting for disability and comorbidities hypothesised to be mediators in the causal pathway between obesity and mortality further attenuated this association [HR: 0.92 (0.80,1.06) p=0.24]. In contrast, obesity at age 30 was strongly associated with mortality [HR: 2.00 (1.65,2.42) p<0.001]. Additionally, weight loss since age-30 was a strong, dose-dependent predictor of mortality independent of enrolment BMI.
The risk of obesity is substantially underestimated when epidemiologic methods do not account for long-term weight changes. Both obesity and weight loss are strongly associated with mortality risk in patients with RA.