The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.Avoid if sensitive or allergic to any ingredients present in Vitamin C products. Vitamin C is generally regarded as safe in amounts normally obtained from foods. Vitamin C supplements are also generally regarded as safe in most individuals in recommended amounts. Vitamin C may cause abdominal cramps or pain, chest pain, dental erosion, dizziness, diarrhea, faintness, fatigue, flushing, gut blockage, headache, heartburn, increased risk of lung cancer, increased risk of Parkinson's disease, inflamed esophagus, injection site discomfort, nausea, red blood cell complications, skin tingling or irritation, slowing of endurance training, thickening of blood vessels close to the heart, urinary complications, and vomiting.
High doses of vitamin C have been associated with multiple adverse effects. These include blood clotting, death (heart-related), kidney stones, pro-oxidant effects, problems with the digestive system, and red blood cell destruction. In cases of toxicity due to massive ingestions of vitamin C, forced fluids, and diuresis may be beneficial. Use cautiously in chronic, large doses. Healthy adults who take chronic large doses of vitamin C may experience low blood levels of vitamin C when they stop taking the high doses and resume normal intake. Vitamin C in high doses appears to interfere with the blood-thinning effects of anticoagulants such as warfarin. Caution is advised in people with bleeding disorders or those taking drugs that affect bleeding. Dosing adjustments may be necessary. Vitamin C may affect blood sugar levels. Caution is advised in people with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist.
Medication adjustments may be necessary. Vitamin C may increase blood pressure. Caution is advised in people with high blood pressure. Use cautiously in people with cancer (e.g. lung), cataracts, glucose-6-phosphate dehydrogenase deficiency, anemia and related conditions, disorders of the gut, kidney stones, or sickle cell disease. Use cautiously in people after angioplasty and in pregnant women at risk of high blood pressure during pregnancy. Use cautiously in greater than recommended doses in breastfeeding women. Use cautiously in people taking antibiotics, anticancer agents, HIV medications, barbiturates, estrogens, fluphenazine, or iron supplements. Use injected vitamin C cautiously, especially in high doses, as it may lead to kidney function problems. Use vitamin C tablets cautiously, as dental erosion may occur from chewing vitamin C tablets often. Avoid in people with known allergy or sensitivity to any ingredients in Vitamin C products. Avoid high doses of vitamin C in people with conditions aggravated by increased acid, such as advanced liver disease, gout, a disease where kidneys fail to remove extra acid from the body, or a disease with early breakdown of red blood cells.
Avoid high doses of vitamin C in people with kidney failure or in those taking agents that may damage the kidneys. Vitamin C intake from food is generally considered safe during pregnancy and breastfeeding. Use cautiously in greater than recommended doses in pregnant and breastfeeding women. Use vitamin C cautiously in those at risk of high blood pressure during pregnancy. This evidence-based monograph was prepared by The Natural Standard Research CollaborationStay Connected With Dr. Weil - Get Free Newsletters Right In Your Inbox Answer: Yes, it's possible to take too much vitamin C. Since vitamin C is water-soluble (excess amounts are excreted and do not accumulate in the body), people sometimes assume there is no harm in taking large doses. However, there are potential short-term and long-term problems with taking high doses (500 to 1,000 mg per day) or very high doses (more than 2,000 mg per day) of vitamin C. Very high doses of vitamin C are known to cause gastric discomfort and diarrhea, and this is the basis for the current upper tolerable daily intake limit of 2,000 mg for adults.
More limited, but concerning, evidence suggests problems with daily doses of just 500 to 1,000 mg of vitamin C. (Keep in mind that the recommended daily intake of vitamin C for adults is only 75 mg to 120 mg, with an additional 35 mg for smokers -- see the RDAs for details). For example, while long-term, low-dose supplementation with vitamin C may help to prevent cataracts, high doses may actually increase the risk. Taking a several hundred milligrams of vitamin C daily may also hamper some of the benefits of endurance exercise, as has been found with high doses of other antioxidant vitamins and supplements. High doses of vitamin C may also reduce the effectiveness of certain medications, and increase the risk of liver damage when taking high doses of Tylenol. They may also interfere with tests for cholesterol and blood sugar, and for blood in the stool. Individuals prone to developing kidney stones or with defects in metabolizing vitamin C or oxalate should also limit vitamin C from supplements.
For more about these effects and the specific amounts of vitamin C associated with them, see the Concerns and Cautions section of the Vitamin C Supplements Review >> You may also be interested in these related CL Answers: Do vitamin C supplements help prevent cataracts? Can vitamin C from a supplement cause blood in the urine and painful urination? Is liposomal vitamin C (sold as Lypo-Spheric) better than other forms of vitamin C? Some websites claim that synthetic vitamin C in supplements may be a combination the active "L" form and the inactive "D" form of ascorbic acid. Should I be concerned? See other recent and popular questions >>We read all questions and try to answer those of popular interest.Is high-dose vitamin C risky? Recently the National Academy of Sciences (NAS) issued dietary antioxidantThe new recommendations call for 90 mg. for vitamin C for healthy adults, up from 60 mg per day under the previous standard. government keeps preaching five servings of fresh fruits and vegetables,
which supplies more than 200 mg. of vitamin C. [Am J Clin Nut 62: 1347-56S, 1995] These two figures do not correlate. Just months before the 90 mg vitamin C recommendation was issued, various government scientists were calling for 120-200 mg per day in published reports. [Proc Natl Acad Sci 93:3704-09, 1996; Nutrition Reviews 57: 222-24, 1999; Am J Clin Nut 69:1086-1107, 1999] One researcher at the Massachusetts Institute of Technology, Laboratory of Human Nutrition, using a technique called suggested that even the 200-mg level was not adequate to meet individual vitamin C needs by as much as 2-3 fold. [Proc Natl Acad Sci 93: 14344,48, 1996] While the Food & Nutrition Board suggested adding another 35 mg of vitamin C for smokers (125 mg total), researchers at the Medical College of Wisconsin found that it takes 200 mg of vitamin C before smokers achieve the levels of ascorbic acid as non-smokers. [Am J Clin Nut 53: 1466-70, 1991]
Other investigators have called for 200-mg daily consumption of vitamin C fo [Ann NY Acad Sci 686: 335-46, 1993] demonstrated that a single 2000 mg dose of vitamin C can completely abolish the typical reduction in blood circulation that occurs while smoking aA 1000 mg dose had no effect. [Microvascular Res 58: 305-11, 1999] What happened to these recommendations? The NAS recommendations conveniently stopped short of recommending levels of vitamin C that would requireThe Academy of Sciences set the tolerable upper limit at 2000 mg, but a recent review indicated doses of vitamin C up to 4000 mg. are [Nut Rev 57: 71-77, 1999] double-blind studies and six non-placebo clinical trials in which up to 10,000 mg of vitamin C was consumed daily for up to 3 years confirm the safety of vitamin C in high doses. [J Am Coll Nut 14: 124-36, 1995] headline in the press release from the National Academy of Sciences concerning antioxidants read "huge doses considered risky."
Furthermore, Maret Traber PhD, a member of the NAS panel, says there is no evidence that proves antioxidant supplements will help people live better [Whole Foods Magazine, August 2000] study, which showed that greater than 300 mg of daily vitamin C male life span by six years, a report that was widely reported in Newsweek [Epidemiology 3: 194-202, 1992] [Epidemiology 11: 440-45, 2000] Furthermore, one study shows that about 294 mg of vitamin C significantly decreases the risk of cataracts compared to 77 mg. per day (about the level set by the Academy of Sciences). [Clin Chem 39: 1305, 1993] much vitamin C a person would have to consume 5 oranges per day. consumption of vitamin C supplements for 10 years or more results in a 77-83 percent reduction in the prevalence of cataracts. [Am J Clin Nut 66: 911-16, 1997] One of the fallacies of current vitamin C research is the use of blood serum levels as the gold standard for establishing recommended daily consumption
A 1991 study, conducted at the USDA Human Nutrition Research Center on Aging at Tufts University, found that there were "striking differ in ocular levels of vitamin C among older adults who consume 148 mg of vitamin C from their daily diet (which is 2.5 times the old 60 mg RDA and 1. times the current 90 mg recommendation) compared to adults who took 2000 mgThe level of vitamin C in the focusing lens and aqueous fluid of the eye increased by 22-32 percent with consumption of 2000 mg of daily vitamin C supplementation, which affords protection againstThus the idea that vitamin C levels reach a saturation point at about 240 mg in the blood serum, and that additional vitamin C is worthless and only washes out in the urine, is dispelled by this research. Eye Research 8: 751-59, 1991] This is the same level of vitamin C that the National Academy of Sciences now considers "risky." [NAS press release April 10, 2000] The message the National Academy of Sciences sends is always the same,
regardless of the evidence, which is that you can get all the nutrients you need from your diet, not pills. But this recommendation comes withThe fine print reads that the NAS recommendation is only for healthy individuals, and it only spells out "the minimum amount of a that has beneficial health effects." The NAS says the effects of antioxidants are "promising but unproven." How much evidence is enough? The answers provided by the NAS Food and Nutrition Board members amount to doublespeak. The discussion becomes almost unintelligible with all the talk about daily value, Recommended Daily Allowance (RDA), USRDA, daily reference intake (DRI) and tolerable upperWhich consumer, let alone rocket scientist, can decipher these standards so they can make an intelligent health decision? One assumption is that people do not need antioxidant supplement until theyBut the Journal of the American Medical Association the destructive process of oxidation is involved in virtually every disease.
[J Am Med Assn 271: 1148-49, 1994] Aging, disease and antioxidant status often parallel each other. Living tissues slowly age or wear out, they don't become ill overnight. For example, the focusing lens of the human eye loses about 1 percent of its clarity for every year of life. universal and slowly progressive with advancing age. By age 60 only about 35 percent of light reaches the retina. By age 85 a person needs a 250-watt light bulb to see what they saw with a 60-watt light bulb when they were 20The level of vitamin C in the lens of the eye has been with severity of cataract. [Internatl J Vitamin Nutr Res 68: 309-15, 1998] If an individual consumes the minimum amount of vitamin C that produces healthful benefits (90 mg. per day by the NAS standards), and waits till develop a cataract to take more vitamin C, it will probably be too late to About 300-2000 mg per day of vitamin C would be required to prevent cataracts, according to the data at hand.