Structural and social determinants of health factors accounted for county-level variation in non-adherence to antihypertensive medication treatment

Background: Non-adherence to antihypertensive medication treatment (AHM) is a complex health behavior with determinants that extend beyond the individual patient. The structural and social determinants of health (SDH) that predispose populations to ill health and unhealthy behaviors could be potential barriers to long-term adherence to AHM. However, the role of SDH in AHM non-adherence have been understudied. Therefore, we aimed to define and identify the SDH factors associated with non-adherence to AHM and to quantify the variation in county-level non-adherence to AHM explained by these factors. Methods: Two cross-sectional datasets, the Centers for Disease Control and Prevention (CDC) Atlas of Heart Disease and Stroke (2014-2016 cycle) and the 2016 County Health Rankings (CHR), were linked to create an analytic dataset. Contextual SDH variables were extracted from both the CDC-CHR linked dataset. County-level prevalence of AHM non-adherence, based on Medicare fee-for-service beneficiaries claims data, was extracted from the CDC Atlas dataset. The CDC measured AHM non-adherence as the Proportion of Days Covered (PDC) with AHM during a 365-day period for Medicare Part D beneficiaries and aggregated these measures at the county-level. We applied Confirmatory Factor Analysis (CFA) to identify the constructs of social determinants of AHM non-adherence. AHM non-adherence variation and its social determinants were measured with structural equation models. Results: Among 3,000 counties in the US, the weighted mean prevalence of AHM non-adherence (PDC<80%) in 2015 was 25.0%, Standard Deviation (SD), 18.8%. AHM non-adherence was directly associated with poverty/food insecurity (beta=0.31, P-value<0.001) and weak social supports (beta=0.27, P-value<0.001), but inversely with healthy built environment (beta=-0.10, P-value=0.02). These three constructs explained a third (R2=30.0%) of the variation in county-level AHM non-adherence. Conclusion: AHM non-adherence varies by geographical location, a third of which is explained by contextual SDH factors including poverty/food insecurity, weak social supports and healthy built environments.