There's been an approx 80% decline in US infant mortality from 1963 to 2023 according to [0]. I know when comparing against pre-industrial society this is a big driver of increased life expectancy. There's another metric that adjusts for this that only looks at the life expectancy of individuals who survive to the age of (iirc) 15, but I don't have time to look it up right now. Perhaps comparing the change in that versus the one that includes the drop in infant mortality would be interesting though.
This exists in a system. We have obesity (caused by several factors, diet and activity levels of course and then the factors into those) along with improved medical care. It's like inflating a balloon with a slow leak. The medical care is propping up our life expectancy numbers while our individual behavior is bringing it down. It'll level out or decline at some point as our obese population continues to become a larger percentage and medical improvements stop happening so regularly.
Because we can all afford to go to the doctor regularly. If treated early, you can live with type 2 diabetes and other obesity related diseases for decades.
Infant mortality, smoking levels, alcohol consumption, social acceptance of driving while intoxicated, car collision safety, etc have all changed significantly in that same time frame.
