Body mass index trend and variability in rheumatoid arthritis

Abstract

Objective: To characterize and compare trends in body mass index (BMI) and variability in BMI between subjects with rheumatoid arthritis (RA) and matched non-RA subjects and to determine predictors of BMI trends and variability within RA subjects.

Methods: This retrospective population-based cohort study included 1114 Olmsted County, Minnesota residents, 558 with incident RA (age ≥ 18 years, 1987 ACR criteria met in 1995-2009) and 556 non-RA subjects from the same underlying population with similar age, sex, and index calendar year. All subjects were followed until death, migration, or 12/31/2018. Generalized linear models with smoothing splines and random effects to account for multiple measurements per subject were used to examine trends in BMI measurements over time.

Results: Mean BMI of patients with incident RA (28.8 kg/m²) was not significantly different from that of non-RA subjects (28.9 kg/m²). There was no significant difference in BMI trends over time between RA and non-RA cohorts, or between seropositive for rheumatoid factor (RF) and/or citrullinated antibody (CCP-antibody) and seronegative RA patients, or between male and female subjects. RA subjects were noted to have significantly higher BMI variability following diagnosis compared to non-RA subjects [difference in standard deviation between RA and non-RA subjects prior to index (p = 0.12), 0-5 years after index (p = 0.044), and 5-15 years after index (p = 0.013)].

Conclusion: The BMI trajectory of the RA population is not significantly different compared to that of the non-RA population, but patients with RA demonstrate higher variability in BMI following diagnosis compared to the non-RA population. Key Points • This study uniquely characterizes longitudinal trajectory in BMI measures and their variability in the RA population versus the non-RA population • This study suggests that RA patients have greater BMI variability compared to the non-RA population, which is highly relevant as BMI variability is increasingly understood as a cardiovascular risk factor.

Keywords: BMI variability; Body mass index; Rheumatoid arthritis.

Figure 1.

BMI trajectory. a) BMI over time by RA status (RA: p=0.058; non-RA: p=0.58). b) BMI over time by age (p=0.49). c) BMI over time from index by serological status (RA only) (p=0.32). d) BMI over time from RA incidence by serological status and sex (p=0.63).

Figure 2.

BMI variability. a) SD of BMI over time from index by RA status (prior to index: p=0.12; 0–5 years post-index: p=0.044; 5–15 years post-index: p=0.013). b) SD of BMI over time from index by serological status (RA only) (prior to index: p=0.97; 0–5 years post-index: p=0.43; 5–15 years post-index: p=0.24). c) SD of BMI over time from index by serological status and sex (prior to index: p<0.001; 0–5 years post-index: p<0.001; 5–15 years post-index: p<0.001).