Medication adherence and functional food use in patients with hypertension: a cross-sectional study

Functional foods are increasingly used by patients with chronic diseases, including hypertension, yet whether their therapeutic use is associated with medication adherence remains unclear. We conducted a cross-sectional study of adults with self-reported hypertension who were receiving antihypertensive medication, using data from the Japan COVID-19 and Society Internet Survey (JACSIS 2024; December 2024-January 2025). Respondents were classified as functional food users if they reported using functional foods specifically to treat hypertension; non-users served as comparators. Medication adherence was measured with the Japanese 8-item Morisky Medication Adherence Scale (MMAS-8); low adherence was defined as MMAS-8 <6. Among 4063 treated hypertensive adults (586 users; 3477 non-users), functional food use was associated with a higher risk of low adherence after adjusting for demographic, socioeconomic, and health-related factors: risk ratio 1.24 (95% CI 1.04-1.48). These findings suggest that therapeutic use of functional foods may be linked to suboptimal adherence to prescribed antihypertensive therapy, warranting further investigation. However, causal relationships cannot be inferred due to the cross-sectional design, and the self-reported nature of both exposures and outcomes may introduce measurement error.