Especially relevant to “red wine is the healthiest type of alcohol to drink - better than drinking no alcohol!”:
People who adopt Conventional Healthy Behavior X (e.g., eat less fat) are more likely to adopt Conventional Healthy Behavior Y (e.g., find a better doctor) than those who don’t. For example, a study found that people who drink a proper amount of wine eat more vegetables. Another reason for a correlation between conventionally-healthy practices is mild depression. People who are mildly depressed are less likely to do twenty different helpful things (including “eat healthy” and “find a better doctor”) than people who are not mildly depressed. (And mild depression seems to be common.)
Obviously, this means that the evidence for things that are well-publicized as healthy (e.g. red wine) grows misleadingly strong over time without careful controls.
(also, newer drugs *may* be adding 2/3 of a year to U.S. life expectancy)