Direct and indirect pathways between low income status and becoming a high-cost health care user in Ontario, Canada: a mediation analysis of health risk behaviors.

Purpose: We investigated natural direct and indirect pathways between low-income status and high-cost user (HCU) transitions considering health risk behaviors as potential mediators.

Methods: We analyzed data from respondents (aged 18+) from four pooled cycles of the Canadian Community Health Survey (2005-2010/2011) linked to administrative data in Ontario, Canada. HCUs were defined as the top 5% of the population, ranked by cost consumption in any of the five years after survey interview. Low-income status was defined from the provincial distribution of self-reported household income, with missing values imputed from neighborhood-level data. In mediation analyses based on marginal structural models, we quantified the contributions of smoking, physical inactivity, alcohol consumption, and body mass index to income-HCU associations.

Results: 115,091 respondents (representative of 9,661,764 Ontarians) were included in the study, of which 7.2% became HCUs. The odds of becoming HCUs were 1.36 times (95% CI: 1.25-1.48) greater for low (vs. high) income status respondents. Smoking, physical activity, alcohol consumption, and body mass index contributed 9.4%, 6.5%, 10.6%, and 4.4% to this association, respectively. Tests for exposure-mediator interactions were not statistically significant.

Conclusions: Health risk behaviors only partially explain income inequalities in future HCU transitions.