AKA - x-ray machines placed in shoe stores so you could stick your foot in, dial up the radiation, and see your wiggling toes in the shoe.
Invented in the 1920s. Debates raged for decades. Outlawed finally in most states in the 1970s.
So for 50 years people thought taking your kid to the shoe store and blasting their feet with radiation was a good idea.
Largely because they had limited data and ability to measure the outcome, as the data became available it became crystal clear that these had the potential to be dramatically harmful.
Even with this lesson in mind I took fish oil for years, despite a lack of clear data.
The study a couple of years ago that linked fish-oil (natural and supplemental) to a 41% increase in prostate cancer / 71% increase in aggressive prostate cancer, reminded me of the flouroscope story. (2)
This Harvard health article, a couple of years old, puts it best:
"How food, and its component molecules, affect the body is largely a mystery. That makes the use of supplements for anything other than treating a deficiency questionable." (3)
(1) http://en.wikipedia.org/wiki/Shoe-fitting_fluoroscope
(2) http://jnci.oxfordjournals.org/content/early/2013/07/09/jnci...
(3) http://www.health.harvard.edu/blog/fish-oil-friend-or-foe-20...