Sex- and Age-Specific Multimorbidity Networks in Middle-aged Inpatients: A Network-based Comparative Study Between China and the United Kingdom

Background and Objectives Multimorbidity is increasingly prevalent among the middle-aged population, yet it is largely often overlooked. We aimed to explore and compare the differences in multimorbidity patterns by sex and age among middle-aged inpatients from China and the United Kingdom (UK). Research Design and Methods We analyzed 184,133 hospitalisation records from Shaanxi, China, and 180,497 from the UK-Biobank for middle-aged populations. Using network analysis, we examined multimorbidity patterns by sex, age groups (40-44, 45-49, 50-54, 55-59 years), and countries. We also identified hub diseases in both sex-specific and sex-age-specific networks and their corresponding roles in forming multimorbidity patterns. Results In both China and the UK, males exhibited higher multimorbidity prevalence (China: 58.51% vs. 55.33%, 1.06x; UK: 31.15% vs. 29.79%, 1.05x) and greater complexity of multimorbidity patterns (China: 1179 patterns vs. 990 patterns, 1.19x; UK: 438 patterns vs. 377 patterns, 1.16x) than females. In sex-specific networks, males in both countries demonstrated the specificity of circulatory, genitourinary, and endocrine/nutritional/metabolic-associated multimorbidity patterns, while females demonstrated specific genitourinary and neoplasm-associated multimorbidity patterns. Hub diseases in these networks are distributed in similar disease categories. In sex-age-specific networks, dominant multimorbidity patterns and hub diseases shifted by age. In males, both countries showed stable but dominating circulatory, endocrine/nutritional/metabolic and digestive-associated multimorbidity patterns with aging. In comparison, Chinese females demonstrated an increase in nervous system-associated multimorbidity patterns and a decrease in genitourinary-associated multimorbidity patterns with ageing; British females demonstrated an increase in mental/behavioural-associated multimorbidity patterns and a stable but dominating genitourinary-associated multimorbidity patterns. Discussion and Implications In both China and the UK, males demonstrated more complex multimorbidity than females. With ageing, multimorbidity patterns are stable in males, while females in China and the UK each develop different and specific multimorbidity patterns. These findings may inform targeted interventions for middle-aged inpatients with multimorbidity by sex and age.