For data on vitamin C and COVID-19, see dietary Supplements in the Time of COVID-19 .
- 1 Introduction
- 2 Recommended Intakes
- 3 Sources of Vitamin C
- 4 Vitamin C Intakes and Status
- 5 Vitamin C Deficiency
- 6 Groups at Risk of Vitamin C Inadequacy
- 7 Vitamin C and Health
- 8 Health Risks from Excessive Vitamin C
- 9 Interactions with Medications
- 10 Vitamin C and Healthful Diets
- 11 Disclaimer
Vitamin C, besides known as L-ascorbic acerb, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. Humans, unlike most animals, are unable to synthesize vitamin C endogenously, so it is an essential dietary component [ 1 ] .
Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters ; vitamin C is besides involved in protein metamorphosis [ 1, 2 ]. Collagen is an necessity component of connective tissue, which plays a vital function in wind curative. Vitamin C is besides an important physiologic antioxidant [ 3 ] and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol ( vitamin E ) [ 4 ]. Ongoing research is examining whether vitamin C, by limiting the damaging effects of spare radicals through its antioxidant bodily process, might help prevent or delay the development of certain cancers, cardiovascular disease, and early diseases in which oxidative stress plays a causal role. In addition to its biosynthetic and antioxidant functions, vitamin C plays an crucial function in immune affair [ 4 ] and improves the concentration of nonheme iron [ 5 ], the kind of iron present in plant-based foods. Insufficient vitamin C consumption causes scurvy, which is characterized by fatigue or languor, far-flung conjunction tissue weakness, and capillary fragility [ 1, 2, 4, 6-9 ].
The intestinal absorption of vitamin C is regulated by at least one specific dose-dependent, active voice conveyer belt [ 4 ]. Cells roll up vitamin C via a second specific transport protein. In vitro studies have found that oxidise vitamin C, or dehydroascorbic acid, enters cells via some facilitated glucose transporters and is then reduced internally to ascorbic acerb. The physiologic importance of dehydroascorbic acid consumption and its contribution to overall vitamin C economy is unknown .
oral vitamin C produces tissue and plasma concentrations that the body tightly controls. approximately 70 % –90 % of vitamin C is absorbed at mince intakes of 30–180 mg/day. however, at doses above 1 g/day, assimilation falls to less than 50 % and absorbed, unmetabolized ascorbic acid is excreted in the urine [ 4 ]. Results from pharmacokinetic studies indicate that oral doses of 1.25 g/day ascorbic acidic produce mean acme plasma vitamin C concentrations of 135 micromol/L, which are about two times higher than those produced by consuming 200–300 mg/day ascorbic acidic from vitamin C-rich foods [ 10 ]. Pharmacokinetic modeling predicts that even doses arsenic senior high school as 3 deoxyguanosine monophosphate ascorbic acid taken every 4 hours would produce acme plasma concentrations of alone 220 micromol/L [ 10 ] .
The sum torso message of vitamin C ranges from 300 magnesium ( at near scurvy ) to about 2 g [ 4 ]. High levels of vitamin C ( millimolar concentrations ) are maintained in cells and tissues, and are highest in leukocytes ( white blood cells ), eyes, adrenal glands, pituitary gland, and brain. relatively broken levels of vitamin C ( micromolar concentrations ) are found in extracellular fluids, such as plasma, crimson blood cells, and saliva [ 4 ] .
Intake recommendations for vitamin C and other nutrients are provided in the Dietary Reference Intakes ( DRIs ) developed by the Food and Nutrition Board ( FNB ) at the Institute of Medicine ( IOM ) of the National Academies ( once National Academy of Sciences ) [ 8 ]. DRI is the cosmopolitan term for a set of reference values used for plan and assessing nutrient intakes of goodly people. These values, which vary by age and gender [ 8 ], include :
- Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
- Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.
- Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
- Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.
table 1 lists the current RDAs for vitamin C [ 8 ]. The RDAs for vitamin C are based on its known physiological and antioxidant functions in white blood cells and are a lot higher than the sum required for protection from lack [ 4, 8, 11 ]. For infants from give birth to 12 months, the FNB established an AI for vitamin C that is equivalent to the beggarly inhalation of vitamin C in healthy, breastfed infants .
|0–6 months||40 mg*||40 mg*|
|7–12 months||50 mg*||50 mg*|
|1–3 years||15 mg||15 mg|
|4–8 years||25 mg||25 mg|
|9–13 years||45 mg||45 mg|
|14–18 years||75 mg||65 mg||80 mg||115 mg|
|19+ years||90 mg||75 mg||85 mg||120 mg|
|Smokers||Individuals who smoke require 35 mg/day
more vitamin C than nonsmokers.
* Adequate Intake ( AI )
Sources of Vitamin C
Fruits and vegetables are the best sources of vitamin C ( see Table 2 ) [ 12 ]. Citrus fruits, tomatoes and tomato juice, and potatoes are major contributors of vitamin C to the american diet [ 8 ]. other good food sources include red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, and cantaloup ( see Table 2 ) [ 8, 12 ]. Although vitamin C is not naturally deliver in grains, it is added to some fortified breakfast cereals. The vitamin C content of food may be reduced by elongated memory and by cooking because ascorbic acid is water soluble and is destroyed by heat [ 6, 8 ]. Steaming or microwaving may lessen cooking losses. fortunately, many of the best food sources of vitamin C, such as fruits and vegetables, are normally consumed naked. Consuming five varied servings of fruits and vegetables a day can provide more than 200 milligram of vitamin C .
|Food||Milligrams (mg) per serving||Percent (%) DV*|
|Red pepper, sweet, raw, ½ cup||95||106|
|Orange juice, ¾ cup||93||103|
|Orange, 1 medium||70||78|
|Grapefruit juice, ¾ cup||70||78|
|Kiwifruit, 1 medium||64||71|
|Green pepper, sweet, raw, ½ cup||60||67|
|Broccoli, cooked, ½ cup||51||57|
|Strawberries, fresh, sliced, ½ cup||49||54|
|Brussels sprouts, cooked, ½ cup||48||53|
|Grapefruit, ½ medium||39||43|
|Broccoli, raw, ½ cup||39||43|
|Tomato juice, ¾ cup||33||37|
|Cantaloupe, ½ cup||29||32|
|Cabbage, cooked, ½ cup||28||31|
|Cauliflower, raw, ½ cup||26||29|
|Potato, baked, 1 medium||17||19|
|Tomato, raw, 1 medium||17||19|
|Spinach, cooked, ½ cup||9||10|
|Green peas, frozen, cooked, ½ cup||8||9|
*DV = Daily Value. The U.S. Food and Drug Administration ( FDA ) developed DVs to help consumers compare the food contents of foods and dietary supplements within the context of a total diet. The DV for vitamin C is 90 magnesium for adults and children age 4 years and older [ 13 ]. FDA does not require food labels to list vitamin C content unless vitamin C has been added to the food. Foods providing 20 % or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV besides contribute to a healthful diet .
The U.S. Department of Agriculture ‘s ( USDA ‘s ) FoodData Central lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin C arranged by nutrient contented and by food name .
Supplements typically contain vitamin C in the form of ascorbic acid, which has equivalent bioavailability to that of naturally occurring ascorbic acidic in foods, such as orange juice and broccoli [ 14-16 ]. other forms of vitamin C supplements include sodium ascorbate ; calcium ascorbate ; other mineral ascorbates ; ascorbic acid with bioflavonoids ; and combination products, such as Ester-C®, which contains calcium ascorbate, dehydroascorbate, calcium threonate, xylonate and lyxonate [ 17 ] .
A few studies in humans have examined whether bioavailability differs among the respective forms of vitamin C. In one study, Ester-C® and ascorbic acid produced the like vitamin C plasma concentrations, but Ester-C® produced significantly higher vitamin C concentrations in leukocytes 24 hours after consumption [ 18 ]. Another analyze found no differences in plasma vitamin C levels or urinary elimination of vitamin C among three different vitamin C sources : ascorbic acid, Ester-C®, and ascorbic acid with bioflavonoids [ 17 ]. These findings, coupled with the relatively low cost of ascorbic acidic, led the authors to conclude that simple ascorbic acerb is the choose source of auxiliary vitamin C [ 17 ] .
Vitamin C Intakes and Status
According to the 2001–2002 National Health and Nutrition Examination Survey ( NHANES ), beggarly intakes of vitamin C are 105.2 mg/day for adult males and 83.6 mg/day for adult females, meeting the presently established RDA for most nonsmoking adults [ 19 ]. Mean intakes for children and adolescents aged 1-18 years range from 75.6 mg/day to 100 mg/day, besides meeting the RDA for these age groups [ 19 ]. Although the 2001–2002 NHANES analysis did not include data for breastfed infants and toddlers, breastmilk is considered an adequate source of vitamin C [ 8, 14 ]. Use of vitamin C-containing supplements is besides relatively common, adding to the sum vitamin C consumption from food and beverages. NHANES data from 1999–2000 bespeak that approximately 35 % of adults take multivitamin supplements ( which typically contain vitamin C ) and 12 % take a separate vitamin C addendum [ 20 ]. According to 1999–2002 NHANES data, approximately 29 % of children take some mannequin of dietary addendum that contains vitamin C [ 21 ] .
Vitamin C status is typically assessed by measuring plasma vitamin C levels [ 4, 14 ]. other measures, such as leukocyte vitamin C concentration, could be more accurate indicators of tissue vitamin C levels, but they are more unmanageable to assess and the results are not constantly authentic [ 4, 9, 14 ] .
Vitamin C Deficiency
Acute vitamin C insufficiency leads to scurvy [ 7, 8, 11 ]. The timeline for the development of abject varies, depending on vitamin C body stores, but signs can appear within 1 calendar month of little or no vitamin C consumption ( below 10 mg/day ) [ 6, 7, 22, 23 ]. initial symptoms can include fatigue ( credibly the consequence of mar carnitine biosynthesis ), malaise, and inflammation of the gums [ 4, 11 ]. As vitamin C insufficiency progresses, collagen synthesis becomes afflicted and connection tissues become weakened, causing petechia, ecchymoses, purpura, articulation pain, poor wound healing, hyperkeratosis, and corkscrew hairs [ 1, 2, 4, 6-8 ]. Additional signs of abject include depression adenine well as conceited, bleeding gums and loosening or passing of teeth due to tissue and capillary fragility [ 6, 8, 9 ]. Iron lack anemia can besides occur ascribable to increased bleed and decrease nonheme iron preoccupation secondary to low vitamin C intake [ 6, 11 ]. In children, cram disease can be present [ 6 ]. Left untreated, abject is fatal [ 6, 9 ] .
Until the end of the eighteenth century, many sailors who ventured on long ocean voyages, with short or no vitamin C inhalation, contracted or died from scurvy. During the mid-1700s, Sir James Lind, a british Navy surgeon, conducted experiments and determined that eating citrus fruits or juices could cure scurvy, although scientists did not prove that ascorbic acid was the active component until 1932 [ 24-26 ] .
nowadays, vitamin C insufficiency and scurvy are rare in developed countries [ 8 ]. Overt lack symptoms occur only if vitamin C intake falls below approximately 10 mg/day for many weeks [ 5-8, 22, 23 ]. Vitamin C lack is rare in develop countries but can placid occur in people with limited food variety .
Groups at Risk of Vitamin C Inadequacy
Vitamin C inadequacy can occur with intakes that fall below the RDA but are above the sum required to prevent overt insufficiency ( approximately 10 mg/day ). The follow groups are more probably than others to be at risk of obtaining insufficient amounts of vitamin C .
Smokers and passive “smokers”
Studies systematically show that smokers have lower plasma and leukocyte vitamin C levels than nonsmokers, due in depart to increased oxidative stress [ 8 ]. For this reason, the IOM concluded that smokers need 35 mg more vitamin C per day than nonsmokers [ 8 ]. exposure to secondhand smoke besides decreases vitamin C levels. Although the IOM was unable to establish a specific vitamin C prerequisite for nonsmokers who are regularly exposed to secondhand roll of tobacco, these individuals should ensure that they meet the RDA for vitamin C [ 4, 8 ] .
Infants fed evaporated or boiled milk
Most infants in develop countries are fed breastmilk and/or baby formula, both of which issue adequate amounts of vitamin C [ 8, 14 ]. For many reasons, feeding infants evaporated or boiled cow ‘s milk is not recommended. This practice can cause vitamin C lack because overawe ‘s milk naturally has very little vitamin C and heat can destroy vitamin C [ 6, 12 ] .
Individuals with limited food variety
Although fruits and vegetables are the best sources of vitamin C, many other foods have belittled amounts of this nutrient. thus, through a vary diet, most people should be able to meet the vitamin C RDA or at least obtain enough to prevent abject. People who have limited food variety—including some aged, destitute individuals who prepare their own food ; people who abuse alcohol or drugs ; food faddists ; people with genial illness ; and, occasionally, children—might not obtain sufficient vitamin C [ 4, 6-9, 11 ] .
People with malabsorption and certain chronic diseases
Some checkup conditions can reduce the absorption of vitamin C and/or increase the come needed by the body. People with severe intestinal malabsorption or cachexia and some cancer patients might be at increase risk of vitamin C insufficiency [ 27 ]. Low vitamin C concentrations can besides occur in patients with end-stage nephritic disease on chronic hemodialysis [ 28 ] .
Vitamin C and Health
due to its affair as an antioxidant and its function in immune routine, vitamin C has been promoted as a mean to help prevent and/or treat numerous health conditions. This section focuses on four diseases and disorders in which vitamin C might play a role : cancer ( including prevention and treatment ), cardiovascular disease, age-related macular degeneration ( AMD ) and cataracts, and the common cold .
epidemiologic tell suggests that higher consumption of fruits and vegetables is associated with lower hazard of most types of cancer, possibly, in region, due to their high vitamin C subject [ 1, 2 ]. Vitamin C can limit the formation of carcinogens, such as nitrosamines [ 2, 29 ], in vivo ; modulate immune reaction [ 2, 4 ] ; and, through its antioxidant function, possibly attenuate oxidative damage that can lead to cancer [ 1 ] .
Most case-control studies have found an inverse association between dietary vitamin C intake and cancers of the lung, breast, colon or rectum, abdomen, oral pit, larynx or throat, and esophagus [ 2, 4 ]. Plasma concentrations of vitamin C are besides lower in people with cancer than controls [ 2 ] .
however, evidence from prospective cohort studies is inconsistent, possibly due to varying intakes of vitamin C among studies. In a cohort of 82,234 women aged 33–60 years from the Nurses ‘ Health Study, consumption of an average of 205 mg/day of vitamin C from food ( highest quintile of inhalation ) compared with an median of 70 mg/day ( lowest quintile of intake ) was associated with a 63 % lower hazard of breast cancer among premenopausal women with a family history of breast cancer [ 30 ]. conversely, Kushi and colleagues did not observe a significantly lower risk of breast cancer among postmenopausal women consuming at least 198 mg/day ( highest quintile of consumption ) of vitamin C from food compared with those consuming less than 87 mg/day ( lowest quintile of intake ) [ 31 ]. A review by Carr and Frei concluded that in the majority of prospective age group studies not reporting a importantly lower cancer risk, most participants had relatively high vitamin C intakes, with intakes higher than 86 mg/day in the lowest quintiles [ 2 ]. Studies reporting importantly lower cancer risk found these associations in individuals with vitamin C intakes of at least 80–110 mg/day, a scope associated with close to vitamin C tissue impregnation [ 2, 22, 32 ] .
evidence from most randomized clinical trials suggests that vitamin C supplementation, normally in combination with other micronutrients, does not affect cancer risk. In the Supplémentation en Vitamines et Minéraux Antioxydants ( SU.VI.MAX ) cogitation, a randomized, double-blind, placebo-controlled clinical trial,13,017 healthy french adults received antioxidant supplement with 120 mg ascorbic acidic, 30 milligram vitamin E, 6 milligram beta-carotene, 100 microgram selenium, and 20 milligram zinc, or placebo [ 33 ]. After a median follow-up time of 7.5 years, antioxidant supplementation lowered full cancer incidence in men, but not in women. In addition, service line antioxidant status was related to cancer hazard in men, but not in women [ 34 ]. Supplements of 500 mg/day vitamin C plus 400 IU vitamin E every early day for a mean follow-up time period of 8 years failed to reduce the hazard of prostate gland or sum cancer compared with placebo in middle-aged and older men participating in the Physicians ‘ Health Study II [ 35 ]. exchangeable findings were reported in women participating in the Women ‘s Antioxidant Cardiovascular Study [ 36 ]. Compared with placebo, supplementation with vitamin C ( 500 mg/day ) for an average of 9.4 years had no significant effect on entire cancer incidence or cancer deathrate. In a large intervention test conducted in Linxian, China, daily supplements of vitamin C ( 120 milligram ) plus molybdenum ( 30 microgram ) for 5–6 years did not significantly affect the risk of developing esophageal or gastric cancer [ 37 ]. furthermore, during 10 years of follow-up, this supplement regimen failed to significantly affect total morbidity or mortality from esophageal, gastric, or other cancers [ 38 ]. A 2008 review of vitamin C and early antioxidant supplements for the prevention of gastrointestinal cancers found no convincing attest that vitamin C ( or beta-carotene, vitamin A, or vitamin E ) prevents gastrointestinal cancers [ 39 ]. A like review by Coulter and colleagues found that vitamin C supplement, in combination with vitamin E, had no significant effect on death risk due to cancer in healthy individuals [ 40 ] .
At this time, the tell is inconsistent on whether dietary vitamin C intake affects cancer risk. Results from most clinical trials suggest that modest vitamin C supplementation alone or with other nutrients offers no benefit in the prevention of cancer .
A hearty limitation in interpreting many of these studies is that investigators did not measure vitamin C concentrations before or after supplement. Plasma and weave concentrations of vitamin C are tightly controlled in humans. At daily intakes of 100 magnesium or higher, cells appear to be saturated and at intakes of at least 200 milligram, plasma concentrations increase lone marginally [ 2, 10, 22, 31, 37 ]. If subjects ‘ vitamin C levels were already close to impregnation at study entrance, supplement would be expected to have made small or no difference on measured outcomes [ 22, 23, 41, 42 ] .
During the 1970s, studies by Cameron, Campbell, and Pauling suggested that high-dose vitamin C has beneficial effects on timbre of life and survival time in patients with end cancer [ 43, 44 ]. however, some subsequent studies—including a randomized, double-blind, placebo-controlled clinical test by Moertel and colleagues at the Flickroom [ 45 ] —did not support these findings. In the Moertel study, patients with advance colorectal cancer who received 10 g/day vitamin C fared no better than those receiving a placebo. The authors of a 2003 recapitulation assessing the effects of vitamin C in patients with advanced cancer concluded that vitamin C confers no significant deathrate profit [ 40 ].
Emerging research suggests that the road of vitamin C presidency ( intravenous vs. oral ) could explain the conflicting findings [ 1, 46, 47 ]. Most intervention trials, including the one conducted by Moertel and colleagues, used only oral government, whereas Cameron and colleagues used a combination of oral and intravenous ( IV ) administration. oral administration of vitamin C, even of very large doses, can raise plasma vitamin C concentrations to a maximum of only 220 micromol/L, whereas IV administration can produce plasma concentrations deoxyadenosine monophosphate high as 26,000 micromol/L [ 47, 48 ]. Concentrations of this order of magnitude are selectively cytotoxic to tumor cells in vitro [ 1, 67 ]. Research in mouse suggests that pharmacological doses of IV vitamin C might show promise in treating otherwise difficult-to-treat tumors [ 49 ]. A high concentration of vitamin C may act as a pro-oxidant and beget hydrogen peroxide that has selective perniciousness toward cancer cells [ 49-51 ]. Based on these findings and a few shell reports of patients with advanced cancers who had unusually long survival times following administration of high-dose IV vitamin C, some researchers support reappraisal of the use of high-dose IV vitamin C as a drug to treat cancer [ 3, 47, 49, 52 ] .
As discussed below, it is uncertain whether auxiliary vitamin C and other antioxidants might interact with chemotherapy and/or radiation sickness [ 53 ]. consequently, individuals undergoing these procedures should consult with their oncologist anterior to taking vitamin C or other antioxidant supplements, particularly in high doses [ 54 ] .
evidence from many epidemiologic studies suggests that high intakes of fruits and vegetables are associated with a reduce risk of cardiovascular disease [ 1, 55, 56 ]. This association might be partially attributable to the antioxidant contented of these foods because oxidative damage, including oxidative modification of low-density lipoproteins, is a major causal agent of cardiovascular disease [ 1, 4, 56 ]. In addition to its antioxidant properties, vitamin C has been shown to reduce monocyte adhesiveness to the endothelium, improve endothelium-dependent azotic oxide production and vasodilation, and reduce vascular smooth-muscle-cell apoptosis, which prevents brass imbalance in atherosclerosis [ 2, 57 ] .
Results from prospective studies examining associations between vitamin C consumption and cardiovascular disease risk are conflicting [ 56 ]. In the Nurses ‘ Health Study, a 16-year prospective study involving 85,118 female nurses, entire consumption of vitamin C from both dietary and auxiliary sources was inversely associated with coronary heart disease risk [ 58 ]. however, consumption of vitamin C from diet alone showed no meaning associations, suggesting that vitamin C supplement users might be at lower risk of coronary thrombosis heart disease. A a lot smaller survey indicated that postmenopausal women with diabetes who took at least 300 mg/day vitamin C supplements had increased cardiovascular disease mortality [ 59 ] .
A prospective survey in 20,649 british adults found that those in the top quartile of baseline plasma vitamin C concentrations had a 42 % lower risk of stroke than those in the bottom quartile [ 60 ]. In male physicians participating in the Physicians ‘ Health Study, function of vitamin C supplements for a hateful of 5.5 years was not associated with a significant decrease in total cardiovascular disease deathrate or coronary heart disease mortality [ 61 ]. A pool psychoanalysis of nine prospective studies that included 293,172 subjects release of coronary heart disease at baseline found that people who took ≥700 mg/day of supplementary vitamin C had a 25 % lower hazard of coronary thrombosis heart disease incidence than those who took no auxiliary vitamin C [ 62 ]. The authors of a 2008 meta-analysis of prospective age group studies, including 14 studies reporting on vitamin C for a median follow-up of 10 years, concluded that dietary, but not supplementary, consumption of vitamin C is inversely associated with coronary thrombosis heart disease risk [ 55 ] .
Results from most clinical intervention trials have failed to show a beneficial effect of vitamin C supplementation on the basal or secondary prevention of cardiovascular disease. In the Women ‘s Antioxidant Cardiovascular Study, a secondary prevention test involving 8,171 women aged 40 years or older with a history of cardiovascular disease, supplementation with 500 mg/day vitamin C for a average of 9.4 years showed no overall effect on cardiovascular events [ 63 ]. similarly, vitamin C supplement ( 500 mg/day ) for a beggarly follow-up of 8 years had no impression on major cardiovascular events in male physicians enrolled in the Physicians ‘ Health Study II [ 64 ] .
other clinical trials have generally examined the effects on cardiovascular disease of supplements combining vitamin C with early antioxidants, such as vitamin E and beta-carotene, making it more unmanageable to isolate the potential contribution of vitamin C. The SU.VI.MAX survey examined the effects of a combination of vitamin C ( 120 mg/day ), vitamin E ( 30 mg/day ), beta-carotene ( 6 mg/day ), selenium ( 100 mcg/day ), and zinc ( 20 mg/day ) in 13,017 french adults from the general population [ 33 ]. After a medial follow-up time of 7.5 years, the compound supplements had no effect on ischemic cardiovascular disease in either men or women. In the Women ‘s Angiographic Vitamin and Estrogen ( WAVE ) study, involving 423 postmenopausal women with at least one coronary thrombosis stenosis of 15 % –75 %, supplements of 500 mg vitamin C plus 400 IU vitamin E doubly per day not only provided no cardiovascular benefit, but importantly increased all-cause deathrate compared with placebo [ 65 ] .
The authors of a 2006 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 golden 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 ]. In this trial, daily vitamin C supplements ( 120 milligram ) plus molybdenum ( 30 microgram ) for 5–6 years significantly reduced the risk of cerebrovascular deaths by 8 % during 10 years of follow-up after the end of the active intervention .
Although the Linxian trial data suggest a potential benefit, overall, the findings from most treatment trials do not provide convincing testify that vitamin C supplements provide protection against cardiovascular disease or reduce its unwholesomeness or deathrate. however, as discussed in the cancer prevention department, clinical trial data for vitamin C are limited by the fact that plasma and tissue concentrations of vitamin C are tightly controlled in humans. If subjects ‘ vitamin C levels were already near to impregnation at study submission, supplement would be expected to have made little or no difference on measured outcomes [ 22, 23, 41, 42 ] .
AMD and cataracts are two of the leadership causes of vision personnel casualty in older individuals. Oxidative tension might contribute to the etiology of both conditions. frankincense, researchers have hypothesized that vitamin C and other antioxidants play a character in the exploitation and/or discussion of these diseases .
A population-based cohort study in the Netherlands found that adults aged 55 years or older who had high dietary intakes of vitamin C a well as beta-carotene, zinc, and vitamin E had a reduced hazard of AMD [ 68 ]. however, most prospective studies do not support these findings [ 69 ]. The authors of a 2007 taxonomic review and meta-analysis of prospective age group studies and randomized clinical trials concluded that the current tell does not support a role for vitamin C and other antioxidants, including antioxidant supplements, in the elementary 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 progress [ 71 ]. The age-related Eye Disease Study ( AREDS ), a big, randomize, placebo-controlled clinical test, evaluated the consequence of high doses of selected antioxidants ( 500 milligram vitamin C, 400 IU vitamin E, 15 magnesium beta-carotene, 80 milligram zinc, and 2 mg copper ) on the exploitation of advanced AMD in 3,597 older individuals with varying degrees of AMD [ 72 ]. After an modal follow-up time period of 6.3 years, participants at high risk of developing promote AMD ( i.e., those with intercede AMD or those with advanced AMD in one eye ) who received the antioxidant supplements had a 28 % lower risk of progress to advanced AMD than participants who received a placebo. A follow-up AREDS2 study confirmed the value of this and like supplement formulations in reducing the progress 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 gamble of cataract formation in some studies [ 2, 4 ]. In a 5-year prospective age group report conducted in Japan, higher dietary vitamin C consumption was associated with a reduce gamble of developing cataracts in a cohort of more than 30,000 adults aged 45–64 years [ 74 ]. Results from two case-control studies indicate that vitamin C intakes greater than 300 mg/day reduce the risk of cataract constitution by 70 % –75 % [ 2, 4 ]. Use of vitamin C supplements, on the other hand, was associated with a 25 % higher risk of age-related cataract extraction among a cohort of 24,593 swedish women aged 49–83 years [ 75 ]. These findings applied to study participants who took relatively high-dose vitamin C supplements ( approximately 1,000 mg/day ) and not to those who took multivitamins containing well less vitamin C ( approximately 60 mg/day ) .
Data from clinical trials are limited. In one study, chinese adults who took daily supplements of 120 mg vitamin C plus 30 microgram molybdenum for 5 years did not have a significantly lower cataract gamble [ 76 ]. however, adults aged 65–74 years who received 180 mg vitamin C plus 30 microgram molybdenum combined with other nutrients in a multivitamin/mineral accessory had a 43 % significantly lower risk of developing nuclear cataracts than those who received a placebo [ 76 ]. In the AREDS report, older individuals who received supplements of 500 mg vitamin C, 400 IU vitamin E, and 15 mg beta-carotene for an average of 6.3 years did not have a significantly lower risk of developing cataracts or of cataract progress than those who received a placebo [ 77 ]. The AREDS2 study, which besides tested formulations containing 500 magnesium vitamin C, confirmed these findings [ 78 ] .
overall, the presently available evidence does not indicate that vitamin C, taken entirely or with other antioxidants, affects the risk of developing AMD, although some tell indicates that the AREDS formulations might slow AMD progress in people at high risk of developing advanced AMD .
The common cold
In the 1970s Linus Pauling suggested that vitamin C could successfully treat and/or prevent the common cold [ 79 ]. Results of subsequent controlled studies have been discrepant, resulting in confusion and controversy, although public matter to in the subject remains high [ 80, 81 ] .
A 2007 Cochrane review examined placebo-controlled trials involving the use of at least 200 mg/day vitamin C taken either continuously as a condom treatment or after the attack of cold symptoms [ 81 ]. condom use of vitamin C did not significantly reduce the gamble of developing a cold in the general population. however, in trials involving marathon runners, skiers, and soldiers exposed to extreme physical practice and/or cold environments, preventive use of vitamin C in doses ranging from 250 mg/day to 1 g/day reduced coldness incidence by 50 %. In the general population, use of condom vitamin C modestly reduced cold duration by 8 % in adults and 14 % in children. When taken after the attack of coldness symptoms, vitamin C did not affect cold duration or symptom severity .
overall, the tell to date suggests that regular intakes of vitamin C at doses of at least 200 mg/day do not reduce the incidence of the park cold in the general population, but such intakes might be helpful in people exposed to extreme physical exercise or cold environments and those with marginal vitamin C condition, such as the aged and chronic smokers [ 81-83 ]. The use of vitamin C supplements might shorten the duration of the coarse cold and better 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 ] .
Health Risks from Excessive Vitamin C
Vitamin C has broken toxicity and is not believed to cause dangerous adverse effects at high intakes [ 8 ]. The most coarse 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 ] .
In postmenopausal women with diabetes who participated in the Iowa Women ‘s Health Study, supplementary ( but not dietary ) vitamin C inhalation ( at least 300 mg/day ) was significantly associated with an increased risk of cardiovascular disease mortality [ 59 ]. The mechanism for this consequence, if real, is not clear and this line up is from a subgroup of patients in an epidemiologic study. No such association has been observed in any other epidemiologic study, so the significance of this receive is uncertain. senior high school vitamin C intakes besides have the electric potential to increase urinary oxalate and uric acid elimination, which could contribute to the geological formation of kidney stones, particularly in individuals with nephritic disorders [ 8 ]. however, studies evaluating the effects on urinary oxalate body waste of vitamin C intakes ranging from 30 mg to 10 g/day have had conflicting results, so it is not clear whether vitamin C actually plays a role in the development of kidney stones [ 8, 85-87 ]. The best testify that vitamin C contributes to kidney stone formation is in patients with preexistent hyperoxaluria [ 23 ] .
due to the enhancement of nonheme iron preoccupation by vitamin C, a theoretical concern is that high vitamin C intakes might cause overindulgence iron absorption. In healthy individuals, this does not appear to be a concern [ 8 ]. however, in individuals with familial hemochromatosis, chronic pulmonary tuberculosis of high doses of vitamin C could exacerbate iron overload and solution in tissue wrong [ 4, 8 ] .
Under certain conditions, vitamin C can act as a pro-oxidant, potentially contributing to oxidative wrong [ 8 ]. A few studies in vitro have suggested that by acting as a pro-oxidant, supplementary oral vitamin C could cause chromosomal and/or DNA damage and possibly contribute to the development of cancer [ 8, 88, 89 ]. however, other studies have not shown increase oxidative damage or increased cancer risk with eminent intakes of vitamin C [ 8, 90 ] .
other reported effects of high intakes of vitamin C admit reduced vitamin B12 and copper levels, accelerated metamorphosis or body waste of ascorbic acid, corrosion of dental enamel, and allergic responses [ 8 ]. however, at least some of these conclusions were a consequence of assay artifact, and extra studies have not confirmed these observations [ 8 ] .
The FNB has established ULs for vitamin C that apply to both food and addendum intakes ( board 3 ) [ 8 ]. long-run 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 aesculapian treatment, but such individuals should be under the care of a doctor [ 8 ] .
|0–12 months||Not possible to establish*||Not possible to establish*|
|1–3 years||400 mg||400 mg|
|4–8 years||650 mg||650 mg|
|9–13 years||1,200 mg||1,200 mg|
|14–18 years||1,800 mg||1,800 mg||1,800 mg||1,800 mg|
|19+ years||2,000 mg||2,000 mg||2,000 mg||2,000 mg|
*Formula and food should be the only sources of vitamin C for infants .
Interactions with Medications
Vitamin C supplements have the electric 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 .
Chemotherapy and radiation
The safety and efficacy of the consumption 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 carry through 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 people report design [ 52 ]. early data suggest that antioxidants might protect normal tissues from chemotherapy- and radiation-induced damage [ 91, 93 ] and/or enhance the potency of conventional cancer discussion [ 95 ]. however, due to the physiologically mean control of vitamin C, it is ill-defined whether oral vitamin C supplements could alter vitamin C concentrations enough to produce the hint effects. Individuals undergoing chemotherapy or radiation sickness should consult with their oncologist anterior to taking vitamin C or other antioxidant supplements, specially in high doses [ 54 ] .
3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins)
Vitamin C, in combination with other antioxidants, may attenuate the increase in high-density lipoprotein levels resulting from combination niacin–simvastatin ( Zocor® ) therapy [ 96, 97 ]. 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 ] .
Vitamin C and Healthful Diets
The federal government ‘s 2020-2025 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 chiefly through foods. … In some cases, fortified foods and dietary supplements are useful when it is not possible differently to meet needs for one or more nutrients ( for example, during specific life stages such as pregnancy ). ”
For more data about building a goodly dietary form, refer to the Dietary Guidelines for Americans and the U.S. Department of Agriculture ‘s MyPlate.
The Dietary Guidelines for Americans describes a healthy dietary design as one that :
- Includes a variety of vegetables; fruits; grains (at least half whole grains); fat-free and low-fat milk, yogurt, and cheese; and oils.
- Fruits, particularly citrus fruits, fruit juices, and many vegetables are excellent sources of vitamin C. Some ready-to-eat breakfast cereals are fortified with vitamin C.
- Includes a variety of protein foods such as lean meats; poultry; eggs; seafood; beans, peas, and lentils; nuts and seeds; and soy products.
- Limits foods and beverages higher in added sugars, saturated fat, and sodium.
- Limits alcoholic beverages.
- Stays within your daily calorie needs.
This fact sail by the National Institutes of Health ( NIH ) Office of Dietary Supplements ( ODS ) provides information that should not take the identify of medical advice. We encourage you to talk to your healthcare providers ( doctor, registered dietician, pharmacist, etc. ) about your sake in, questions about, or consumption of dietary supplements and what may be best for your overall health. Any mention in this issue of a specific merchandise or serve, or recommendation from an arrangement or professional society, does not represent an endorsement by ODS of that product, service, or adept advice .