Vitamin C, a water-soluble vitamin, is found in abundance in citrus fruits and other fruits and vegetables. The Linus Pauling Institute indicates that there's no scientific evidence that large amounts of supplemental vitamin C have caused toxicity, nor are they generally threatening to your health. However, too much supplemental vitamin C can cause unpleasant side effects -- and chances are you don't need it.
Vitamin C, or L-ascorbic acid, is an essential nutrient, which means you must obtain it from your diet because your body cannot make it in sufficient quantity to meet its needs. You can obtain it from foods and beverages or dietary supplements. Vitamin C is necessary for tissue growth and repair. It's also an antioxidant vitamin that may protect your cells from the damaging effects of free radicals. A 1/2 cup of raw green or red pepper, a 3/4-cup serving of orange or grapefruit juice or a medium orange or kiwifruit gives you 100 percent or more of your daily value, or DV, for vitamin C, based on a 2,000-calorie diet.
The recommended daily intake for vitamin C for women and men ages 19 and up is 75 and 90 mg a day, respectively. Smokers in the same age group require 110 and 125 mg of vitamin C daily, respectively. Pregnant women need between 80 and 85 mg, and nursing women need 115 to 120 mg. Most people get the necessary amount of vitamin C from their daily diets, notes MayoClinic.com.
Vitamin C Toxicity
The tolerable upper intake level, or UL, of vitamin C for adults ages 19 and older is 2,000 mg a day. The Linus Pauling Institute indicates that health complications associated with megadoses of vitamin C are "suggested" through animal testing and isolated case reports. MayoClinic.com states that side effects associated with large doses of vitamin C include nausea, vomiting, diarrhea, stomach cramps, sleeplessness and headache. Kidney stores are another possible result of taking too much vitamin C. People with thalassemia or hemochromatosis may experience iron overload with megadoses. However, vitamin C taken in doses at or below the UL does not seem to result in adverse effects in healthy people.
Vitamin C and Cancer
The Merck Manuals Online Medical Library states that some people take up to 10 g of vitamin C every day to reduce the duration of a viral infection or prevent, treat or cure serious health conditions such as atherosclerosis and cancer. An review of trials and meta-analysis published in the July 2006 issue of "Journal of General Internal Medicine" examined the effects of supplemental vitamin C and vitamin E in cancer survivors. The researchers noted that the reviewed literature does not support the hypothesis that the use of supplements of vitamin C or vitamin E helps prevent and/or treat cancer. There were isolated findings of benefit, which require confirmation.