Association of Income Inequality and Sleep Duration With Cardiovascular Outcomes in China and the UK

BACKGROUND: Cardiovascular diseases (CVDs) are a major global health issue, influenced by income level and sleep duration. OBJECTIVES: This study sought to assess the impact of income inequality and sleep duration on CVD outcomes in China and the United Kingdom. METHODS: We analyzed data from the China Kadoorie Biobank (CKB) (n = 486,131) and UK Biobank (UKB) (n = 403,858). Income level was categorized into low, medium, and high based on the annual household income, and sleep duration into short (<7 hours), optimal (7-9 hours), and long (>9 hours). Cox models estimated HRs for income level, sleep duration, and CVD outcomes. RESULTS: A total of 134,227 incident CVD cases and 16,852 deaths were identified. Low income was associated with higher CVD incidence and mortality in both cohorts (P < 0.001). Short and long sleep durations increased CVD incidence in both cohorts (P < 0.05), except for long sleep and ischemic heart disease in the CKB. Long sleep duration was associated with higher CVD mortality in both cohorts, whereas short sleep duration increased ischemic heart disease risk in the UKB. Compared with individuals of high income and optimal sleep duration, low income was associated with higher CVD risk across all sleep categories. Medium income raised CVD incidence risk in all sleep categories, with mortality associations varying by sleep duration between the CKB and the UKB. CONCLUSIONS: Income level and sleep duration independently and jointly affect CVD incidence and mortality. Low income and suboptimal sleep duration are detrimental to cardiovascular health, highlighting the need for public health strategies to address income disparities and promote optimal sleep for CVD prevention.