So people kind of knew asbestos was harmful wayyy before it mostly stopped being used in 1979 (USA). But, it was still used constantly in many industries and ended up everywhere. What do you think is an example of something we find out is DRASTICALLY harmful 10-50 years from now? My guess would be screen time.
Got to say the obvious: sugar.
Industry sugar is just very bad for us for multiple reasons but it’s used everywhere because of addictive properties.
Go research the sugar cartel and the sugar Vs fat thing which brought the US to fat free stuff which massively raised obesity.