Wonder if its some sort of chemical/food additive, but which one?
Why does it have to be "one" ? Between sodas, alcohol, ultra processed meats, ultra processed vegetarian alternatives, way too much sugar, constant snacking, &c. you have plenty of nasty things to worry about. Then you add sedentarity and obesity to the mix, we're really not helping our bodies, they're amazing machines so they continue to chug for years until they cannot anymore and by then the damages are irreversible.
Compared to the ideal, perhaps, but compared to the past I don’t think this one has increased. Though the supply may have become more adulterated with additives.