The association between total social exposure and incident multimorbidity: A population-based cohort study.

Background: Multimorbidity, the co-occurrence of two or more chronic conditions, is associated with the social determinants of health. Using comprehensive linked population-representative data, we sought to understand the combined effect of multiple social determinants on multimorbidity incidence in Ontario, Canada. Methods: Ontario respondents aged 20-55 in 2001-2011 cycles of the Canadian Community Health Survey were linked to administrative health data ascertain multimorbidity status until 2022. Additive total social exposure (TSE) was generated by summing 12 measures of social disadvantage captured from the survey. Weighted-additive TSE included 15 measures of social disadvantage summed across 5 equally weighted domains. Hazard ratios for the association between each TSE measure and multimorbidity were estimated using competing risk Cox-proportional hazards models. All analyses were sex-stratified. Results: Both additive and weighted-additive TSE were associated with an increased risk of multimorbidity among females and males. A social gradient was observed for multimorbidity risk in all models. While adjusted models were attenuated, an increased risk of multimorbidity was observed among those experiencing the most social disadvantage, compared to those with the least social disadvantage in additive (HR Females = 2.16; 95%CI = 1.63, 2.86; HR Males = 1.90; 95%CI = 1.52, 2.38) and weighted-additive (HR Females = 1.94; 95%CI = 1.49, 2.53; HR Males = 1.72; 95%CI = 1.41, 2.10) models. The observed social gradient was retained. Conclusions: These findings demonstrate the importance of considering the cumulative effects of multiple social determinants of health on multimorbidity.