Understanding the twentieth-century decline in chronic conditions among older men.

I argue that the shift from manual to white-collar jobs and reduced exposure to infectious disease were important determinants of declines in chronic disease rates among older men from the early 1900s to the 1970s and 1980s. The average decline in chronic respiratory problems, valvular heart disease, arteriosclerosis, and joint and back problems was about 66%. Occupational shifts accounted for 29% of the decline; the decreased prevalence of infectious disease accounted for 18%; the remainder are unexplained. The duration of chronic conditions has remained unchanged since the early 1900s, but when disability is measured by difficulty in walking, men with chronic conditions are less disabled now than they were in the past.