We don't really know the situation with C. The urine tube is cleaned but only for a while. We are the only creatures who cant produce it. Some animals produce 200 mg/kg, a 70kg goat makes about 13000 mg. Our RDA is based on scurvy which seems something you'd want to stay far away from. I hear you can safely increase the dosage until you get digestive issues (farting) Nobel laureate Linus Pauling (chemist) lived to be 93 taking 18000 mg per day.