Deaths of young adults in 2023 were 70% higher than they would have been in if trends from before 2011 had continued.
"One surprising thing about the increases in these causes of death are that these are causes of death that primarily kill people at much older ages," said Elizabeth Wrigley-Field, associate professor of sociology and study author.
The study looked at over three million deaths among Americans aged 25-44 during the period 1999-2023.
The researchers identified two separate trends in mortality: an increase between 1999 and 2011, and a sharp increase from 2011 to 2019, which grew even sharper from 2020 to 2023.
Unnatural causes such as drug overdoses were the leading cause of deaths during the study period, accounting for a third of all deaths. Drug overdoses have been the significant biggest cause since 2014, with a significant increase since 2020, for reasons the study authors do not explain.
The contribution of cardio-metabolic conditions, including conditions related to heart and hormone function, as well as nutrition, was also substantial.
Compared to trends before 2011, deaths from most causes were significantly higher in 2023 than would be expected. Excess mortality was 35% greater in 2019, then tripled during the pandemic, before falling. Nevertheless, excess mortality in 2023 is still 70% higher than would be expected if pre-2011 trends had continued.
"The fact that we saw a real growth in mortality at these relatively young ages is very worrying because it suggests that many more deaths may come in the future as these cohorts age into midlife and beyond, if these trends aren't reversed before then," Professor Wrigley-Field added.
The pandemic is suggested as one reason for the spike in excess mortality, but longer term causes, such as the dislocations caused by the economic crash of 2008, are also suggested.