Risks with High Doses

Vitamin C is relatively safe at high doses,but intake of doses higher than 2 g/day may result in diarrhea, nausea, stomach cramping, excess urination, and skin rashes [54]. More recently, 4 g/day has been said to be well-tolerated and safe, except in some patients with renal dysfunction [55]. In rare cases, daily 2-g doses have been associated with kidney stones [56]. Intake of greater than 1 g/day increases oxalate excretion without clinical consequence in normal healthy individuals but could lead to adverse consequences in those with underlying renal disease. Dietary needs of vitamin C are increased by smoking, pollutants, aspirin, alcohol, estrogen, antibiotics, and corticosteroids. It may also interact with various laboratory tests, causing false readings [7].