Vitamin C, which is also called ascorbic acid, is a water-soluble vitamin required for the synthesis of neurotransmitters and collagen. It also has antioxidant properties that can protect molecules in the body from damage by oxidative free radicals. Supplements containing vitamin C are available over-the-counter and are generally safe and well-tolerated, although some side effects may occur if you take high doses.
As a water-soluble vitamin, most excess vitamin C is flushed from the body in urine. As a result, it does not build up in your system and cases of vitamin C toxicity are rare. The recommended dietary allowance for women is 75 milligrams daily, while men should consume 90 milligrams every day. If you smoke, you should add another 35 milligrams because smokers need more antioxidant protection, according to the Linus Pauling Institute. The Institute of Medicine established a tolerable upper intake level of 2,000 milligrams. If you consume more than that from food or supplements, you may experience side effects, but you're not likely to get that much through your diet.
The most common side effects from high doses of vitamin C are upset stomach and diarrhea. Other gastrointestinal symptoms have also been reported, such as abdominal cramps, headache, heartburn and vomiting. These symptoms are generally not serious and usually go away as soon as the high doses of vitamin C are stopped. These symptoms are caused by the osmotic effect that the excess vitamin C has on the gastrointestinal tract, explains the Office of Dietary Supplements. A large concentration of vitamin C in the intestines causes more water to be pulled into the intestines, causing cramping and diarrhea.
Risk of Kidney Stones
Vitamin C can increase the levels of oxalate in your urine, which may also raise your risk of developing kidney stones. Research studies to date have produced mixed results, sometimes showing a relationship between excessive vitamin C and calcium oxalate stones, while other studies do not support this association. However, if you have a history of kidney stones, you should limit your vitamin C consumption to no more than 100 milligrams daily, according to information from New York University's Langone Medical Center.
Vitamin C may reduce the effectiveness of some types of prescription medications including medications used to treat cancer, high cholesterol and AIDS. It may also interfere with the activity of blood-thinning medications, such as warfarin, that are used to treat blood clots, according to MedlinePlus. Since vitamin C boosts the absorption of nonheme iron, you should not take high-dose supplements together with iron supplements. Avoid taking excessive vitamin C if you have iron-related illnesses, such as thalessemia or hemochromatosis. If you have these conditions or take any prescription medications, talk to your physician before taking vitamin C supplements.