If one takes in more than the recommended amount of vitamins (e.g. vitamin c from a lot of oranges), does the body get rid of it; or are the vitamins saved and used up overtime?
Depends on the Vitamin. 99% of the time it will just be flushed out your body. Its especially hard to overdose on water-soluble vitamins. However taking large doses of certain vitamins can cause symptoms. This is known as hypervitaminosis and can be induced when taking a surplus amount of fat-soluble vitamins (A, D, E, K). This is very rare though.
The body gets rid of most of it. But some of them will be absorbed, and it can have adverse effects on the body after prolonged consumption.
For example, too much vitamin D and you may end up with too much calcium in the blood. This can cause hypercalcemia, which may weaken your bones and cause kidney stones.
You can poison yourself with too much iron; usually happens with children since they’re smaller eating too many chewable multi vitamins.
Oh, you’ll also overdoes on Vitamin A if you eat Polar Bear liver