Synergistic effects of hypertension and diabetes on cardiovascular risk in elderly: Comparative longitudinal analysis of CHARLS and HRS

AIMS: The aim of this study was to quantify the interaction between hypertension and diabetes on cardiovascular disease risk in elderly adults, using data from the CHARLS and HRS cohorts. Competing risk models accounting for mortality were employed in the analysis. MATERIALS AND METHODS: This is a prospective analysis of 18 647 participants aged ≥60 years, drawn from two major longitudinal studies: the China Health and Retirement Longitudinal Study (CHARLS, n = 9823, 2011-2020) and the Health and Retirement Study (HRS, n = 8824, 2010-2020). Participants had no baseline cardiovascular disease. The primary endpoints included stroke, myocardial infarction, heart failure, and cardiovascular mortality. Interactions between hypertension and diabetes were assessed using Cox proportional hazards and Fine-Grey competing risk models, with both multiplicative and additive approaches applied. RESULTS: Over median follow-up of 7.8 years (CHARLS) and 8.2 years (HRS), 1909 cardiovascular events occurred. Comorbid hypertension-diabetes showed elevated risk versus neither condition. Significant additive interactions emerged consistently: RERI 0.75 (95% CI: 0.19-1.31) in CHARLS and 0.84 (95% CI: 0.21-1.47) in HRS, with 28-31% excess risk attributable to interaction. Synergy indices confirmed super-additive effects. Stroke showed strongest interaction (RERI ~0.9, SI ~1.8), while myocardial infarction demonstrated minimal synergy. Effects were amplified in participants aged 60-74 and females. CONCLUSIONS: This analysis shows that hypertension and diabetes together increase cardiovascular risk in elderly individuals by about 30%. The findings are consistent across different ethnic groups and healthcare systems, suggesting universal biological mechanisms. This supports updating risk assessments and enhancing preventive strategies, especially for cerebrovascular risks in the elderly.