What have you heard about Vit C messing with the kidneys?
There have been various people claiming high dose vit C can have a negative impact on kidney function and cause kidney stones. This is usually the result of a poorly designed test where not all factors are taken into account. Reduced urine flow and concentrated urine appear to be the chief physiological factors in kidney problems.
kidney stones occure when oxalic acid precipitates out of solution only from a neutral or alkaline solution—pH 7 to pH 10. Urine pH in those consuming ten grams of Vitamin C daily is about 6. Even in diabetics who take this large amount of C (10 grams).
The vit C kidney stone issue is a myth just like Iodine causing problems.