I don't have a citation, just a hunch this coincided with the chemical revolution of the 1950's. I strongly suspect though smoking may have been correlated with poor health before then, that there probably were not 400K Americans dying of smoking-related illnesses every year until after the chemical revolution and the cigarette industry intentionally taking advantage of addiction by standardizing on precise and elevated nicotine-dosing as well as the infusion of 300 some carcinogens. So Big Tobacco loses a big case in the 1990's, must pay billions of dollars for intentionally making their product extremely addicting, but this punishment is lifted in the early 2000's without full payment. But, astoundingly, the Big Tobacco case and settlement overlooked a major detail (that the intentional addition of 300+ carcinogens, for the purposes of increasing addiction, were, in fact, extremely deadly, and that the industrialized process of creating deadly cigarettes isn't at all necessary for producing and selling tobacco products), which allowed Big Tobacco to continue creating a far more deadly and far more addicting product than tobacco, and thus, inexplicably actually, go on killing 400K Americans annually, and however many more worldwide. It really is the craziest thing.