Good question. But there is no way to prove that I would’ve been worse off had I not taken the many vitamins I take. I was taking a supplement for high cholesterol, Red Yeast Rice, that supposedly lowered cholesterol. I started it right after having my cholesterol tested and took it for 6 months and had it tested again. There was no difference in my cholesterol. It did not lower it. I quit taking it. If there were a way to test all of them, I would say they probably do not work. But my grandmother, who died at 98 swore by them, so I take them.