Quantifying the global population residing at different altitudes

Background Human adaptation to low oxygen environments at high altitude has been extensively studied, with physiological responses commonly described as respiratory, hematological, cardiovascular, and metabolic. Although altitude is often classified into low, moderate, high, and very high ranges, the global number and distribution of people living at different elevations remain difficult to quantify because of population mobility and changing settlement patterns. Objective To quantify the global population living across different altitude ranges and describe its geographic distribution using geospatial and population databases. Methods We conducted a global ecological analysis using the World Cities Database Pro version, refreshed on May 11, 2025, GPS elevation data obtained through the dCode tool, and elevation data from NASA's Shuttle Radar Topography Mission. More than 1.8 million cities were classified according to two altitude frameworks: the classical classification of low altitude below 2,500 m and high altitude at or above 2,500 m; and the International Society for Mountain Medicine classification, defined as low altitude below 1,500 m, moderate altitude from 1,500 to 2,500 m, high altitude from 2,500 to 3,500 m, and very high altitude from 3,500 to 5,500 m. Results Overall, 99.26% of the global population, approximately 7.95 billion people, lives below 2,500 m, where 98.86% of cities are located. In contrast, only 0.74% of the global population, approximately 57.8 million people, resides above 2,500 m. High-altitude populations are concentrated mainly in the Andes, the Himalayas, and the Ethiopian Highlands. Population density declined sharply with increasing altitude. Conclusions The vast majority of the global population lives below 2,500 m, while a relatively small but epidemiologically important population resides at high altitude. These findings provide a global baseline for understanding altitude-related population distribution and support future research on the health effects of chronic high-altitude exposure. They may also inform public health strategies for populations living in or migrating to high-altitude environments.