People knew smoking was a bad idea before 1964

One of the great rewards of digging into old pop culture -- not the retconned, re-edited, just-the-hits version but the raw data -- is the way you keep running into counter-examples of conventional wisdom about the periods that produced the art. Fortunately, with online resources such as Internet Archive or Digital Comics Museum (which supplied the ad below), you can dig to your heart's content.

There's a popular genre of health narratives that run along roughly the same lines as the "last person you suspect" school of mystery fiction. In this genre, the revelation of some major effect (like smoking causes cancer) catches everyone off guard.

As far as I can tell, when you dig into these cases, you generally find that, if the magnitudes really are big, people will have started to notice that something was going on. For example, this ad (from the still extant Weider company) was running a decade before the Surgeon General's admittedly groundbreaking report. You can argue that people didn't realize just how strong the relationship was and the report certainly added a degree of certainty that was perhaps unprecedented for this type of  public health question but  people suspected smoking was unhealthy for a long time.

From the horror comic Dark Mysteries published in 1954.

We covered similar territory back in 2011.