Side effects of vitamin c at 1000mg a day - is that a lot?

Usually none & no: Vitamin c is extremely safe. Excessive doses (usually over 5000 mg a day) can cause a laxative effect. Vit. C can interact with certain medications, esp. Coumadin (warfarin) (which interacts with everything!). Concerns that high doses of vit c can cause kidney stones are unproven, in fact there is no good evidence of harm from high doses of c. See http://lpi.Oregonstate.Edu/infocenter/vitamins/vitaminc/.