Aim: To explore whether long-term adherence to preventive statin therapy depends on socioeconomic position (SEP).
Methods: A cohort of individuals without established cardiovascular disease (CVD) or diabetes initiating preventive statin therapy during 2002-2005 was followed in the individual-level Danish registries for 4 years or until censoring events (death, emigration, CVD or diabetes). Only individuals aged 40-84 years for whom information was available on the SEP indicators, education and income were included (N = 76,038). Two different aspects of poor adherence were applied as outcome measures: (1) Proportion of days covered (PDC) with medication below 80 %, assuming a daily dose of one tablet (continuity); (2) Discontinuation defined as a gap between two consecutive prescriptions exceeding 365 days (persistence). Stratum-specific logistic regression analyses were applied to estimate the odds ratio (OR) for PDC <80 % across SEP, adjusting for age and hypertension. Hazard ratio (HR) for discontinuation was estimated by Cox regression analyses.
Results: Adjusting mutually for income and education, the OR for PDC <80 % decreased with increasing income. Comparing the highest income quintile with the lowest, the OR were 0.64 (95 % Confidence Interval 0.64-0.65) and 0.73 (0.73-0.74) in men aged 40-64 and 65-84 years, respectively; in women, the figures were 0.79 (0.79-0.79) and 0.95 (0.94-0.95), respectively. While observed increases in adherence with longer education in unadjusted analyses were attenuated after adjustment for income among men, the potential inverse relationship between length of education and adherence was enhanced among women. Applying discontinuation as outcome, analogous differences were demonstrated.
Conclusion: Adherence to preventive statin therapy in Denmark decreases with decreasing income-especially in men aged 40-64 years.