The researchers showed that compared to previous generations, members of Generation X and Generation Y showed poorer physical health, higher levels of unhealthy behaviour such as alcohol use and smoking, and more depression and anxiety.
According to the lead researcher, Hui Zheng from The Ohio State University, the results suggest the likelihood of higher levels of diseases and more deaths in younger generations than seen in the past.
"The worsening health profiles we found in Gen X and Gen Y is alarming," Zheng said.
"If we don't find a way to slow this trend, we are potentially going to see an expansion of morbidity and mortality rates in the United States as these generations get older," Zheng added.
For the study, published in the American Journal of Epidemiology, the team examined used data from the National Health and Nutrition Examination Survey 1988-2016 (62,833 respondents) and the National Health Interview Survey 1997-2018 (625,221 respondents), both conducted by the National Center for Health Statistics.
They also used one marker of chronic inflammation, low urinary albumin, and one additional marker of renal function, creatinine clearance.
The researchers found that the measures of physical health have worsened from the Baby Boomer generation through Gen X (born 1965-80) and Gen Y (born 1981-99).
"The declining health trends in recent generations is a shocking finding. It suggests we may have a challenging health prospect in the US in coming years," Zheng said.
Zheng said it is beyond the scope of the study to comprehensively explain the reasons behind the health decline. But the researchers did check two factors. They found smoking couldn't explain the decline. Obesity could help explain the increase in metabolic syndrome, but not the increases seen in chronic inflammation.