I'm referring specifically to DCA here -- the tests with lab rats seem to produce far better results than with people.
Possible reason? Lab rats are fed a highly nutritious diet, and don't eat junk food. And of course they don't smoke, drink, or take recreational drugs.
In addition, lab rats produce their own vitamin C in their bodies, as do all mammals except for apes, man, and guinea pigs. It is estimated by some authors that if human beings made their own vitamin C as most animals do, our bodies would produce 13,000 milligrams of vitamin C a day!