The rising incidence of stroke in the young: epidemiology, causes and global impact.

Although reductions in stroke incidence have been reported over recent decades particularly in high-income countries, there has been a worrying trend since the start of the 21st century: stroke incidence in younger individuals (< 55 years) has not showed a similar decrease than at older ages. In high-income countries, several population-based studies have found an increase in the incidence of stroke at younger ages since 2000, reaching up to 90% in Oxfordshire, UK (2010-2018 vs 1981-1986) and 97% in Cincinnati, US (2010 vs 1993-1994). A similar picture has also been documented in low- and middle-income countries, both in population-based studies (Joinville, Brazil, 35% increase in 2012-2013 vs 2005-2006) and in the Global Burden of Diseases Study. The exact reasons for this very different picture seen in younger individuals are unknown. One possibility is that traditional modifiable risk factors are increasingly prevalent and often undertreated at younger ages. However, studies have also found increases in the incidence of young-onset cryptogenic stroke and in people with no traditional modifiable risk factors, suggesting a role for emerging risk factors. Potential culprits might include air pollution, long working hours, psychosocial stress, prior autoimmune diseases, and illicit drug use, although further research is required to determine whether these emerging risk factors are causally related to stroke at younger ages. Without further intervention, the global burden of stroke at younger ages is projected to increase further in the coming years. Therefore, there is an urgent need to better understand the drivers of these time trends in incidence, to potentially alleviate the individual and societal impacts of stroke in the young. In this narrative review, we examine the recent global changes in stroke epidemiology at younger ages, their potential drivers, and their projected consequences.