Workplace social capital and adherence to antihypertensive medication: A cohort study

Background: While hypertension is a common and treatable health problem, adherence to antihypertensive medication remains a challenge. This study examines the hypothesis that workplace social capital may influence adherence to antihypertensive medication among hypertensive employees. Methodology/Principal Findings: We linked survey responses to nationwide pharmacy records for a cohort of 3515 hypertensive employees (mean age 53.9 years, 76% women) who required continuous antihypertensive drug therapy (the Finnish Public Sector study). A standard scale was used to measure workplace social capital from co-workers' assessments and self-reports in 2000-2004. Non-adherence to antihypertensive medication was determined based on the number of days-not-treated at the year following the survey using comprehensive prescription records. Negative binomial regression models were conducted adjusting for socio-demographic characteristics, duration of hypertension, behaviour-related risk factors, and co-morbid conditions. The overall rate of days-not-treated was 20.7 per person-year (78% had no days-not-treated). Higher age, obesity, and presence of somatic co-morbidities were all associated with better adherence, but this was not the case for co-worker-assessed or self-reported workplace social capital. The rate of days-not-treated was 19.7 per person-year in the bottom fourth of co-worker-assessed workplace social capital, compared to 20.4 in the top fourth. The corresponding rate ratio from the fully-adjusted model was 0.95 (95% confidence interval (CI) 0.58-1.56). In a subgroup of 907 new users of antihypertensive medication this rate ratio was 0.98 (95% CI 0.42-2.29). Conclusions/Significance: We found no consistent evidence to support the hypothesized effect of workplace social capital on adherence to drug therapy among employees with chronic hypertension.