Vitamin C, which is also called ascorbic acid, is a water-soluble vitamin required for several biochemical reactions, including the synthesis of neurotransmitters and collagen. Vitamin C 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, especially at high doses.
Toxicity
As a water-soluble vitamin, most excess vitamin C is flushed from the body in urine, and cases of vitamin C toxicity are rare. The National Institute of Medicine has set a Tolerable Upper Intake Level, or UL, for vitamin C of 2000 mg per day for adults over the age of 19 years. Doses above 2000 mg per day are more likely to cause side effects.
Side Effects
The most common side effects from high doses of vitamin C are upset stomach and diarrhea. These symptoms are generally not serious and usually stop as soon as the high doses of vitamin C are stopped. Other gastrointestinal symptoms have also been reported, such as abdominal cramps. 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.
Additional Possible Risks
Additional symptoms of high doses of vitamin C have occasionally been reported, such as an increased risk of cardiovascular disease in postmenopausal women with diabetes; however, this effect was only observed in one study, reports the Office of Dietary Supplements. The risk of kidney stones may be increased by large doses of vitamin C, although the evidence on this topic is conflicting and inconclusive. Reduced levels of copper and vitamin B-12 have been reported following large doses of vitamin C, but these effects have also not been confirmed in subsequent studies.
Drug Interactions
Vitamin C may reduce the activity of blood-thinning medications, such as warfarin, that are used to treat blood clots. Again, the evidence supporting this conclusion is inconclusive, but if you are taking blood thinners, you should consult your doctor before taking vitamin C. Some evidence suggests that vitamin C may reduce the effectiveness of medications called statins, which are used to treat high cholesterol. While several studies have found contradictory data on this interaction, you should still ask your doctor before taking vitamin C if you have a prescription for statins, recommends the Linus Pauling Institute at Oregon State University.
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