Can You Overdose on Vitamin C?

The importance of vitamin C in the diet has been known ever since it was observed that European sailors on long voyages often sickened and died of a mysterious disease that caused swelling of their hands, feet and gums. It turned out to be the result of a vitamin C deficiency disorder called scurvy that causes a number of unpleasant symptoms, including muscle and tissue hemorrhaging. If foods or supplements containing vitamin C are not consumed promptly, scurvy progresses to extreme exhaustion, kidney and pulmonary problems, diarrhea and death. Once the cure for scurvy was found, sea voyages always included a supply of citrus fruits. Sailors in the British navy became known as "limeys" because they brought limes or oranges along with them to avoid scurvy.

Humans, along with chimpanzees, fruit bats and guinea pigs, are the only mammals unable to synthesize vitamin C in the body. There is no question that vitamin C performs a lot of vital functions. It helps synthesize collagen, which is present in blood vessels, tendons, ligaments, and bone. It is also involved in the synthesis of norepinephrine, a neurotransmitter involved in brain function, and carnitine, which has to do with fat transit and its conversion to energy. Vitamin C may also play a role in cholesterol metabolism. It is an antioxidant that protects molecules such as proteins, fats, carbohydrates, DNA and RNA from free radical damage.

The late Nobel laureate and chemist Linus Pauling was a 20th century crusader for the benefits of megadoses of vitamin C. He observed that taking 3 grams a day made him feel better and seemed to prevent the colds he once suffered from. After studying the scientific research and using himself as a guinea pig, Pauling came to believe that a minimal dose of 250 milligrams a day to up to 10 grams a day of vitamin C offered protection from a number of bacterial and viral infections as well as chronic diseases. He was often ridiculed by his peers for his controversial position, but Pauling may have had the last laugh: he died at the ripe old age of 93 after decades of practicing what he preached regarding vitamin C.

Besides citrus fruits, foods containing vitamin C include tomatoes, broccoli, Brussels sprouts, spinach, green papers, rose hips, black currants, cucumbers, asparagus and lettuce. These foods are best eaten raw, as cooking can destroy vitamin C. Most adults need some vitamin C supplementation. The federal government currently recommends a minimum of 90 milligrams a day for adult males and 75 milligrams a day for adult females. In contrast, the Linus Pauling Institute suggests a minimum dose of 400 milligrams a day for adults.

But despite the many benefits of vitamin C, sometimes too much of a good thing can be bad. According to government researchers, more than 2 grams per day may cause upset stomach, diarrhea, and even kidney stones and gout. In addition, if you suffer from hemochromatosis, thalassemia, or a history of kidney disease, you should probably avoid megadoses of vitamin C, advises Robert Jacob, Ph.D., a research chemist.

On the other hand, Jane Higdon, Ph.D. of the Linus Pauling Institute argues that although megadoses of vitamin C have been blamed for everything from genetic mutations, birth defects, cancer, heart disease, "rebound scurvy", kidney stones, oxidative damage, excess iron absorption, vitamin B-12 deficiency, to erosion of dental enamel, no study has definitively proven any of the above.

However, the Linus Pauling Institute does concede that megadoses of vitamin C may impact the effectiveness of blood thinners (anticoagulant medications) like warfarin, and suggests that anyone taking these drugs should limit their vitamin C intake to 1 gram a day. Another potential problem is that high doses of vitamin C may affect the reading of some laboratory tests such as as serum bilirubin and creatinine, so it's important to inform your doctor if you are taking large amounts of vitamin C.

Until additional research comes up with more solid conclusions, it's probably advisable not to take more than 2 grams of vitamin C a day, because besides causing digestive upset in some individuals, excess vitamin C might end up just making your urine healthier.