https://www.history.com/this-day-in-history/surgeon-general-announces-link-between-smoking-cigarettes-and-cancer?cmpid=email-hist-tdih-2021-0 [login to see] 1&om_rid=
United States Surgeon General Luther Terry knew his report was a bombshell. He intentionally chose to release it on January 11, 1964, a Saturday, so as to limit its immediate effects on the stock market. It was on this date that, on behalf of the U.S. Government, Terry announced a definitive link between smoking and cancer.
The link had long been suspected. Anecdotal evidence had always pointed to negative health effects from smoking, and by the 1930s physicians were noticing an increase in lung cancer cases. The first medical studies that raised serious concerns were published in Great Britain in the late 1940s.