Purpose To investigate associations of obesity and tobacco smoking with SLE patients’ health-related quality of life (HRQoL), pain, fatigue and functional disability.

Methods Patients from the Linköping University Hospital with an SLE diagnosis according to the 1982 ACR or the 2012 SLICC criteria (n=325) were included in the present cross-sectional analysis of data captured at visits between January 2008 and September 2021. Among consecutive visits, the first visit with complete demographic, clinical and patient-reported data was selected for the present analysis.

Body mass index categories were based on the WHO classification: underweight (BMI< 18.5 kg/m2), normal weight (18.5≤ BMI <25 kg/m2), pre-obesity (25≤ BMI <30 kg/m2) and obesity (BMI ≥30 kg/m2). Smoking status was self-reported and categorised as never, prior and ongoing smoker. HRQoL was self-reported using the 3-level EuroQoL 5-Dimension (EQ-5D-3L) index scores. Visual analogue scales (VAS; 0–100) were used to self-report fatigue, pain and well-being within the preceding 7 days. Functional disability was evaluated using the Swedish version of the Health Assessment Questionnaires Disability Index (HAQ-DI). Disease activity was evaluated using the clinical (c)SLEDAI-2K (serology excluded). Comparisons of continuous data between different BMI and smoking categories were performed using the Mann-Whitney U test and Kruskal-Wallis test. Multivariable linear regression analysis was employed to assess independence and priority of contributors to HRQoL and functional impairment.

Results In total, 111 patients were pre-obese and 55 were obese, whereas 103 were prior smokers and 39 were ongoing smokers. Compared with normal weight, obese individuals reported lower EQ-5D-3L index score [0.73 (0.36–0.80) versus 0.78 (0.68–0.85); P=0.014], as well as higher VAS fatigue [50.0 (27.0–72.5) versus 32.0 (6.5–59.5); P=0.008], VAS pain [40.0 (11.0–67.0) versus 20.5 (5.3–46.5); P=0.011] and HAQ scores [0.63 (0.13–1.13) versus 0.13 (0.0–0.63); P<0.001]. Similarly, ongoing smokers reported higher VAS fatigue [56.0 (28.0–78.0) versus 32.0 (8.0–58.0); P=0.001], VAS pain [45.0 (18.0–62.0) versus 18.0 (5.0–39.8); P=0.001] and HAQ scores [0.63 (0.13–1.13) versus 0.13 (0.0–0.63); P=0.001] compared with individuals who were never exposed to tobacco smoking. There were no differences across groups regarding cSLEDAI-2K scores.

In multivariable linear regression models, obesity and current tobacco smoking were independently associated with lower EQ-5D-3L index scores (β=-0.12; P=0.021 and β=-0.11; P=0.029, respectively), and higher VAS fatigue (β=12.8; P=0.007 and β=17.5; P<0.001), VAS pain (β=12.1; P=0.004 and β=15.5; P<0.001), VAS well-being (β=9.6; P=0.028 and β=9.8; P=0.035) and HAQ scores (β=0.30; P=0.001 and β=0.27; P=0.007), but not with cSLEDAI-2K (β=-0.73; P=0.189 and β=0.34; P=0.572).

Conclusions In a Swedish SLE population, obesity and tobacco smoking were independently associated with worse outcomes - compared with normal weight patients and individuals who never smoked, respectively - regarding HRQoL, fatigue, pain and functional disability but not with clinical disease activity.