The vast majority of 40 to 60 year olds I know have no underlying health problems.
But 'people Greenman knows' is not a scientifically-selected sampling of the population!
It probably depends a lot on how they are defining 'underlying health problems'. They don't really seem to explain that (athlete's foot? migraines? a bad knee?)
I wonder whether 'being overweight' is considered as an "underlying health problem"? I saw one report making a big deal out of the fact that 65% of those who died were overweight - when I suspect that's pretty much in line with the percentage of the general population, so doesn't mean much.
Diabetes is pretty common, that's 1 in 10 of the US population, and if you include pre-diabetes it's nearly 1 in 3.