Spatial Epidemiology of the Ischemic Heart Disease–Asthma Comorbidity: A Global Analysis of Burden Patterns, Risk Drivers, and a Composite Risk Index

Background: Although ischemic heart disease (IHD) and asthma are major contributors to the global disease burden, the geographical distribution patterns of their comorbidity and its macro-level drivers remain unclear. This study aims to analyze the global spatial distribution of IHD-asthma comorbidity and to identify the key risk factors driving this comorbid pattern. Methods: Based on a secondary analysis of the Global Burden of Disease Study 2021, this study categorized 204 countries and territories worldwide into three spatial patterns—namely “concordant type”, “IHD-dominant type”, and “asthma-dominant type”—using the quartile method of disability-adjusted life years (DALYs). A three-stage screening approach was employed to identify significant risk factors: random forest modeling combined with Shapley additive explanations was first used to rank and select candidate variables, followed by negative binomial regression analysis to confirm significant associations. Furthermore, population attributable fraction and a composite risk index were constructed to quantify cumulative exposure levels. Results: Approximately one-quarter of countries worldwide exhibit a “concordant pattern” of disease burden levels, primarily located in Asia, Africa, and Oceania. Thirteen significant risk factors were identified, with deficiency in omega-6 polyunsaturated fatty acids and iron deficiency being common risk factors for both diseases. Overall, 43.083% of IHD DALYs and 28.963% of asthma DALYs were attributable to the combined exposure to their respective risk factors. Conclusion: The global joint burden of IHD and asthma exhibits substantial spatial heterogeneity, with particularly severe challenges in socioeconomically resource-limited regions of Africa and Asia. Comprehensive strategies integrating nutritional interventions, environmental improvements, and metabolic risk control are crucial for mitigating the global burden of cardiopulmonary comorbidities. Plain Language Summary: Why was the study done? Ischemic heart disease and asthma are among the world’s most common chronic diseases. When people live with both conditions, they face unique health challenges. Yet researchers have not fully explored where this combination appears most often or what drives it. What did the researchers do and find? Our team used data from the Global Burden of Disease 2021 study to map how ischemic heart disease and asthma co-occur across 204 countries and territories. We combined spatial analysis, machine learning, and statistical models to identify geographic patterns and key risk factors. We found that nearly one in four countries carries a high burden of both diseases simultaneously — a pattern we call “concordant”. These countries cluster mainly in Africa, Asia, and Oceania. We identified 13 significant risk factors. Two — low intake of omega-6 fats (a type of healthy dietary fat) and iron deficiency — increased the risk of both diseases. Others affected only one condition: kidney dysfunction raised ischemic heart disease risk, while household air pollution from solid fuels raised asthma risk. We also created a composite risk index to measure each country’s overall risk exposure, revealing that nations in Africa and Asia face the greatest cumulative risk. What do these results mean? These results show that ischemic heart disease and asthma should be treated as interconnected health problems. Strategies targeting their shared risk factors — such as improving nutrition and reducing indoor air pollution — could ease the burden of both diseases, especially in the hardest-hit regions.