“May all sentient beings be free of pain and suffering. May all sentient beings experience eternal joy and happiness. gate gate pāragate pārasaṃgate bodhi svāhā.”
And while the body does rid itself of some excess, the excess amount itself and the process of doing so can cause problems with other vitamins and minerals and be hard on the organs like the liver and kidneys. For example, excess calcium contributes to kidney stones. And other things, like iron, the body has no mechanism (aside from bleeding) to discard.
Now, if I have a GOOD day, and cover all the food groups, get raw leafies, nuts, fruits, steamed veggies, different beans and grains, etc... Then I don't really bother with them...
...but, if I'm broke and living off of ramen noodles and PB&J's...then yeah, I'll definitely take my supplements.
For without it, we would be lost.