I'd say it started early, when Edward Bernays was enacting his public relations projects with propaganda techniques and the Rockefeller's took over the medical and dental fields. Television had a role as well. Society was changing to processed food as being safer and better, doctors were given bleached white coats and godly status, natural childbirth and breastfeeding were replaced with medicated births and formula. So I'm guessing in the late 20's to the 50's when society shifted to the "experts".