Foods don't contain that much vitamin c though. A typical orange might have 50 mg of vitamin C, so to get 4 grams of vitamin C from oranges, you would have to eat 80 of them a day!(Not a good idea, as this would give you terrible diahrrea, and would also give you too many calories). The better vitamin c supplements are buffered(ie. calcium or magnesium ascorbate, which is vitamin c with calcium or magnesium) and also contain citrus bioflavonoids which work synergistically with the vitamin c.

"High doses of C can damage the kidneys over time, correct?"

Too much taken long term might lead to kidney stones, especially if one doesn't drink enough water. I take only 2 grams a day of vitamin c, but increase this greatly for short periods of time if I get a high fever.