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Preventing preeclampsia may be as simple as taking an aspirin. Evidence from many epidemiological studies suggests that high intakes of fruits and vegetables are associated with a reduced risk of cardiovascular disease [ 1 , 55 , 56 ]. This association might be partly attributable to the antioxidant content of these foods because oxidative damage, including oxidative modification of low-density lipoproteins, is a major cause of cardiovascular disease [ 1 , 4 , 56 ].
In addition to its antioxidant properties, vitamin C has been shown to reduce monocyte adherence to the endothelium, improve endothelium-dependent nitric oxide production and vasodilation, and reduce vascular smooth-muscle-cell apoptosis, which prevents plaque instability in atherosclerosis [ 2 , 57 ].
Results from prospective studies examining associations between vitamin C intake and cardiovascular disease risk are conflicting [ 56 ]. In the Nurses' Health Study, a year prospective study involving 85, female nurses, total intake of vitamin C from both dietary and supplemental sources was inversely associated with coronary heart disease risk [ 58 ]. However, intake of vitamin C from diet alone showed no significant associations, suggesting that vitamin C supplement users might be at lower risk of coronary heart disease.
In male physicians participating in the Physicians' Health Study, use of vitamin C supplements for a mean of 5. The authors of a meta-analysis of prospective cohort studies, including 14 studies reporting on vitamin C for a median follow-up of 10 years, concluded that dietary, but not supplemental, intake of vitamin C is inversely associated with coronary heart disease risk [ 55 ]. Results from most clinical intervention trials have failed to show a beneficial effect of vitamin C supplementation on the primary or secondary prevention of cardiovascular disease.
Other clinical trials have generally examined the effects on cardiovascular disease of supplements combining vitamin C with other antioxidants, such as vitamin E and beta-carotene, making it more difficult to isolate the potential contribution of vitamin C. The SU. The authors of a meta-analysis of randomized controlled trials concluded that antioxidant supplements vitamins C and E and beta-carotene or selenium do not affect the progression of atherosclerosis [ 66 ].
Similarly, a systematic review of vitamin C's effects on the prevention and treatment of cardiovascular disease found that vitamin C did not have favorable effects on cardiovascular disease prevention [ 67 ]. Since then, researchers have published follow-up data from the Linxian trial, a population nutrition intervention trial conducted in China [ 38 ].
Although the Linxian trial data suggest a possible benefit, overall, the findings from most intervention trials do not provide convincing evidence that vitamin C supplements provide protection against cardiovascular disease or reduce its morbidity or mortality. However, as discussed in the cancer prevention section, clinical trial data for vitamin C are limited by the fact that plasma and tissue concentrations of vitamin C are tightly controlled in humans.
AMD and cataracts are two of the leading causes of vision loss in older individuals. Oxidative stress might contribute to the etiology of both conditions. A population-based cohort study in the Netherlands found that adults aged 55 years or older who had high dietary intakes of vitamin C as well as beta-carotene, zinc, and vitamin E had a reduced risk of AMD [ 68 ].
However, most prospective studies do not support these findings [ 69 ]. The authors of a systematic review and meta-analysis of prospective cohort studies and randomized clinical trials concluded that the current evidence does not support a role for vitamin C and other antioxidants, including antioxidant supplements, in the primary prevention of early AMD [ 70 ]. Although research has not shown that antioxidants play a role in AMD development, some evidence suggests that they might help slow AMD progression [ 71 ].
After an average follow-up period of 6. A follow-up AREDS2 study confirmed the value of this and similar supplement formulations in reducing the progression of AMD over a median follow-up period of 5 years [ 73 ]. High dietary intakes of vitamin C and higher plasma ascorbate concentrations have been associated with a lower risk of cataract formation in some studies [ 2 , 4 ]. In a 5-year prospective cohort study conducted in Japan, higher dietary vitamin C intake was associated with a reduced risk of developing cataracts in a cohort of more than 30, adults aged 45—64 years [ 74 ].
Data from clinical trials are limited. In one study, Chinese adults who took daily supplements of mg vitamin C plus 30 mcg molybdenum for 5 years did not have a significantly lower cataract risk [ 76 ]. Overall, the currently available evidence does not indicate that vitamin C, taken alone or with other antioxidants, affects the risk of developing AMD, although some evidence indicates that the AREDS formulations might slow AMD progression in people at high risk of developing advanced AMD.
Results of subsequent controlled studies have been inconsistent, resulting in confusion and controversy, although public interest in the subject remains high [ 80 , 81 ]. Prophylactic use of vitamin C did not significantly reduce the risk of developing a cold in the general population.
When taken after the onset of cold symptoms, vitamin C did not affect cold duration or symptom severity. The use of vitamin C supplements might shorten the duration of the common cold and ameliorate symptom severity in the general population [ 80 , 83 ], possibly due to the anti-histamine effect of high-dose vitamin C [ 84 ]. However, taking vitamin C after the onset of cold symptoms does not appear to be beneficial [ 81 ].
Vitamin C has low toxicity and is not believed to cause serious adverse effects at high intakes [ 8 ]. The most common complaints are diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances due to the osmotic effect of unabsorbed vitamin C in the gastrointestinal tract [ 4 , 8 ]. The mechanism for this effect, if real, is not clear and this finding is from a subgroup of patients in an epidemiological study. No such association has been observed in any other epidemiological study, so the significance of this finding is uncertain.
High vitamin C intakes also have the potential to increase urinary oxalate and uric acid excretion, which could contribute to the formation of kidney stones, especially in individuals with renal disorders [ 8 ]. The best evidence that vitamin C contributes to kidney stone formation is in patients with pre-existing hyperoxaluria [ 23 ].
Due to the enhancement of nonheme iron absorption by vitamin C, a theoretical concern is that high vitamin C intakes might cause excess iron absorption. In healthy individuals, this does not appear to be a concern [ 8 ]. However, in individuals with hereditary hemochromatosis, chronic consumption of high doses of vitamin C could exacerbate iron overload and result in tissue damage [ 4 , 8 ]. Under certain conditions, vitamin C can act as a pro-oxidant, potentially contributing to oxidative damage [ 8 ].
However, other studies have not shown increased oxidative damage or increased cancer risk with high intakes of vitamin C [ 8 , 90 ]. Other reported effects of high intakes of vitamin C include reduced vitamin B12 and copper levels, accelerated metabolism or excretion of ascorbic acid, erosion of dental enamel, and allergic responses [ 8 ].
However, at least some of these conclusions were a consequence of assay artifact, and additional studies have not confirmed these observations [ 8 ]. Long-term intakes of vitamin C above the UL may increase the risk of adverse health effects. The ULs do not apply to individuals receiving vitamin C for medical treatment, but such individuals should be under the care of a physician [ 8 ].
Vitamin C supplements have the potential to interact with several types of medications. A few examples are provided below. Individuals taking these medications on a regular basis should discuss their vitamin C intakes with their healthcare providers.
The safety and efficacy of the use of vitamin C and other antioxidants during cancer treatment is controversial [ 53 , 91 , 92 ]. Some data indicate that antioxidants might protect tumor cells from the action of radiation therapy and chemotherapeutic agents, such as cyclophosphamide, chlorambucil, carmustine, busulfan, thiotepa, and doxorubicin [ 54 , 91 , 93 , 94 ].
At least some of these data have been criticized because of poor study design [ 52 ]. However, due to the physiologically tight control of vitamin C, it is unclear whether oral vitamin C supplements could alter vitamin C concentrations enough to produce the suggested effects. Individuals undergoing chemotherapy or radiation should consult with their oncologist prior to taking vitamin C or other antioxidant supplements, especially in high doses [ 54 ].
It is not known whether this interaction occurs with other lipid-altering regimens [ 54 ]. Healthcare providers should monitor lipid levels in individuals taking both statins and antioxidant supplements [ 54 ].
The federal government's Dietary Guidelines for Americans notes that "Because foods provide an array of nutrients and other components that have benefits for health, nutritional needs should be met primarily through foods. In some cases, fortified foods and dietary supplements are useful when it is not possible otherwise to meet needs for one or more nutrients e. For more information about building a healthy dietary pattern, refer to the Dietary Guidelines for Americans and the U.
Department of Agriculture's MyPlate. This fact sheet by the Office of Dietary Supplements ODS provides information that should not take the place of medical advice. We encourage you to talk to your healthcare providers doctor, registered dietitian, pharmacist, etc.
Any mention in this publication of a specific product or service, or recommendation from an organization or professional society, does not represent an endorsement by ODS of that product, service, or expert advice. Updated: March 26, History of changes to this fact sheet.
Find ODS on:. Strengthening Knowledge and Understanding of Dietary Supplements. Health Information Health Information. New developments and novel therapeutic perspectives for vitamin C. J Nutr ; Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. Am J Clin Nutr ; Ascorbate is an outstanding antioxidant in human blood plasma. Vitamin C function and status in chronic disease.
Nutr Clin Care ; Vitamin C ascorbic acid : new roles, new requirements? Nutr Rev ; An orange a day keeps the doctor away: scurvy in the year Pediatrics ;E Old world meets modern: a case report of scurvy.
Although there is little robust research to support the claims of their effectiveness, some vitamins may help increase blood flow.
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Share on Pinterest It is usually safe to frequently eat foods high in vitamin C. How much vitamin C is too much? Severe side effects.
Share on Pinterest Kidney stones are a possible consequence of too much vitamin C supplementation. How much vitamin C should I take? Vitamin C and pregnancy. Share on Pinterest A pregnant woman may wish to take a vitamin C supplement if they have trouble getting enough from their diet. Latest news Scientists identify new cause of vascular injury in type 2 diabetes. Adolescent depression: Could school screening help? Related Coverage.
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