It's a little tricky knowing just how much vitamin C will do the trick. Two oft-cited studies used either 1000 or 2000 mg/day. Other smaller studies show benefit at 125 to 250 mg/day. Of course, a small dose could have as noticeable an effect as a large dose - if the large dose was taken in one fell swoop. Like most vitamin supplements, the more we take at one time, the less of it we absorb. And intestinal bacteria just love that unabsorbed vitamin C, a love made palpable though cramping, bloating, and diarrhea.
Since I'm not in the market for that kind of love, and since I'm not a devotee of super-sized supplements, I'll opt for the citrus, berries, and ...
Oh! Look at this, FRE ... One spear of raw broccoli has 134 mg of vitamin C!
More on Intelligent Design
Vitamin C, also known as ascorbate, can be manufactured in vivo - in the body - from a molecule of glucose ... that is, in most mammals save for primates1. A human is a primate. Dogs are not primates. Yep, dogs can make all their vitamin C from a simple sugar. Maybe this is why the incessant barking of my neighbor's dog Farley is never curtailed by a bout of hay fever. Lucky dog.
1 Primates lack one important vitamin C synthesizing enzyme: gulonolactone oxidase.