Background & Aims
Pain is common among individuals of higher body weight. Biomedical explanations (e.g., mechanical loading on joints, systemic inflammation) have historically been used to explain this relationship but data suggest they only partially account for the association. Discrimination has been identified as a potential contributor to the onset of pain, as well as greater distress in the context of pain. Weight-related discrimination, reflecting the perception of negative treatment of individuals of higher body weight, is common. Indeed, several analyses have linked weight-related stigma to pain symptoms among individuals of higher weight, but the existing evidence has relied on cross-sectional data with small samples that are primarily comprised of women. The aim of this study is to investigate weight-related discrimination as a mediator of the longitudinal relationship between body weight and pain among a large sample of adults from the English Longitudinal Study of Ageing (ELSA) ) cohort.
Methods
ELSA is a longitudinal panel study of adults aged 50 and older living in England. Data for the current study were taken from three consecutive waves of data collection to provide temporal ordering to evaluate weight-related discrimination as a mediator of the body weight and pain relationship. Demographic data, Body Mass Index (BMI), and self-reported pain (dichotomized as no/mild or moderate/severe pain) were collected at wave 4 (2008-2009). Perceived weight discrimination (dichotomized as ever versus never) was assessed at wave 5 (2010-2011) and pain was reassessed at wave 6 (2012-2013). Generalized linear models were used to estimate the direct effect of BMI at wave 4 (assessed continuously and dichotomized to reflect obesity status (yes/no)) on pain symptoms at wave 6, and the indirect effect of BMI on pain via weight discrimination at wave 5. Models were adjusted for demographics (age, sex, ethnicity, household non-pension wealth, and marital status) and pain at wave 4.
Results
N=5362 individuals provided complete data and were included in the analysis (55% female, 98% white, 65±8.5 years old, BMI 28.1±5.0 kg/m2, 30% with BMI consistent with obesity). Approximately 25% (n=1383) reported moderate/severe pain and 4% (n=217) reported a history of perceived weight discrimination. The direct effect of BMI (measured continuously) on future pain (b=1.05 SE=0.01, p<.01) and the indirect effect through weight discrimination were both significant (b=1.00 SE=0.002, p=.05.) Weight discrimination accounted for 7% of the total effect. The direct effect of obesity status was significant (b=1.43 SE=0.11, p<.01) but the indirect effect of weight discrimination was not (p=.13). Post hoc analyses were conducted to evaluate the indirect effect of BMI on pain among only individuals with no/mild pain at baseline (n=3979.) The direct and indirect pathways were significant for continuous BMI and obesity status (ps<.05) with weight discrimination accounting for 14-25% of the effect.
Conclusions
Higher BMI at baseline predicted greater likelihood of moderate/severe pain symptoms up to four years later among a large cohort of middle aged and older adults living in England. This relationship was regardless of baseline pain symptoms and partially mediated by perceived weight discrimination. Obesity status also predicted future pain, but the relationship was not mediated by weight discrimination. The mediating role of weight discrimination predicting future pain was especially pronounced among individuals with no/mild pain at baseline, suggesting this may be an important target to prevent transition to more severe pain among individuals of higher BMI. There are limitations including brief pain and weight discrimination measures and the observational nature of the data. However, the longitudinal design, temporal order of key variables, and inclusion of important conceptual covariates increases confidence in the possibility that weight discrimination may play an overlooked role.
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