Diverging Pre-Pandemic Mortality Trends: Age-Specific and Cause-Specific Patterns Across High-Income Countries

Background: Mortality rates have declined across most high-income countries for decades, but recent evidence suggests a slowdown in improvements or a shift to increasing mortality, particularly among working-age populations. The international distribution and drivers of these trends remain incompletely understood. Methods: Mortality trends during 2012-2019 were analysed using all-cause and cause-specific data from 30 countries. Trends were estimated via linear regression. K-means clustering with Dynamic Time Warping identified countries and ICD-10 chapters with similar temporal trajectories. Results: Trends varied substantially by nation. While Japan, Switzerland, and the Republic of Korea maintained consistent declines in all-cause mortality rates, increases were concentrated in the United States, Canada, and the United Kingdom, most prominently in persons aged 30-59 years. However, cause-specific analysis showed that rising mortality was not confined to these countries: most countries exhibited increases in at least one ICD-10 chapter, with several European countries showing increases across multiple chapters. Across countries, a small set of causes recurred among increasing trends, including external causes (self-harm, drug poisoning) at younger ages and chronic conditions (cardiovascular and liver diseases, specific cancers) in mid-life. Notably, ill-defined causes of death consistently appeared among the increasing causes across countries and age groups. Conclusions: Mortality increases in the 2010s were geographically more widespread than previously recognized. The recurrent rise in mortality from ill-defined causes suggests that an important component of mortality change remains poorly characterized. These findings indicate that stalled health progress is a systemic challenge across many high-income societies.