Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, vitamin c and cold, vitamin c and adelle davis 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 also involved in protein metabolism vitamin c and cold 12 ]. Collagen is an essential vitamin c and cold of connective tissue, which plays a vital role in wound healing.
Vitamin C is also an important physiological 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 free radicals through its antioxidant activity, might help prevent or delay the development of certain cancers, cardiovascular disease, vitamin c and cold, and other diseases in which oxidative stress plays a vitamin c and cold role.
In addition to its biosynthetic and antioxidant functions, vitamin C plays an important role in immune function [ 4 ] and improves the pvc posts and caps of nonheme iron [ 5 ], the form of iron present in plant-based foods. Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, widespread connective tissue weakness, and capillary fragility [ 124].
The intestinal absorption of vitamin C is regulated by at least one specific dose-dependent, active transporter [ 4 ]. Cells accumulate vitamin C via a second specific transport protein. In vitro studies have found that oxidized vitamin C, or dehydroascorbic acid, enters cells via some facilitated glucose transporters and vitamin c and cold then reduced internally to ascorbic acid.
The physiologic importance of dehydroascorbic acid uptake and its contribution to overall vitamin C economy is unknown.
Oral vitamin C produces tissue and plasma concentrations that the body tightly controls. Results from pharmacokinetic studies indicate that oral doses of 1. The total body content of vitamin C ranges from mg 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 cellseyes, adrenal glands, pituitary gland, and brain. Relatively low levels of vitamin C micromolar concentrations are found in extracellular fluids, such as plasma, red blood cells, vitamin c and cold, and saliva [ 4 ].
DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender [ 8 ], include:. Table 1 lists the current RDAs for vitamin C [ 8 ]. The RDAs for vitamin C are based on vitamin c and cold known physiological and antioxidant vitamin c and cold in white blood cells and are much higher than the amount required for protection from deficiency [ 4811 ].
For infants from birth to 12 months, the FNB established an AI for vitamin C that is equivalent to the mean intake of vitamin C in healthy, breastfed infants. 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 cantaloupe see Table 2 [ 812 ]. Although vitamin C is not naturally present in grains, vitamin c and cold, it is added to some fortified breakfast cereals. The vitamin C content of food may be reduced by prolonged storage and by cooking because ascorbic acid is water soluble and is destroyed by heat [ 68 ].
Steaming or microwaving may lessen cooking losses. Fortunately, many of the best food sources of vitamin C, such as fruits and vegetables, are usually consumed raw. Consuming five varied servings of fruits and vegetables a day can provide more than mg of vitamin C. Food and Drug Administration FDA developed DVs to help consumers compare the nutrient contents of products within the context of a total diet. The DV for vitamin C used for the values in Table 2 is 60 mg for adults and children age vitamin c and cold years and older vitamin c and cold 13 ].
This DV, however, is changing to 90 mg as the updated Nutrition and Supplement Facts labels are implemented [ 14 ]. The updated labels and DVs must appear on food products and dietary supplements beginning in Januarybut they can be used now [ 15 ].
FDA requires current food labels to list vitamin C content, but this requirement will be dropped with the updated labels. Supplements typically contain vitamin C in the form of ascorbic acid, which has equivalent bioavailability to that of naturally occurring ascorbic acid in foods, such as orange juice and broccoli [ ].
A few studies in humans have examined whether bioavailability differs among the various forms of vitamin C. Another study found no differences in plasma vitamin C levels or urinary excretion of vitamin C among three different vitamin Vitamin c and cold sources: These findings, coupled with the relatively low cost of ascorbic acid, vitamin c and cold, led the authors to conclude that simple ascorbic acid is the preferred source of supplemental vitamin C [ 19 ].
Mean intakes for children and adolescents aged years range from Although the — NHANES analysis did not include data for breastfed infants and toddlers, breastmilk is considered an adequate source of vitamin C [ 816 ], vitamin c and cold.
Use of vitamin C-containing supplements is also relatively common, adding to the total vitamin C intake from food and beverages. Vitamin C status is typically assessed by measuring plasma vitamin C levels [ 416 ]. Other measures, such as leukocyte vitamin C concentration, could be more accurate indicators of tissue vitamin C levels, but they are more difficult to assess and the results are not always reliable [ 4916 ].
Acute vitamin C deficiency leads to scurvy [ 78vitamin c and cold, 11 ]. Initial symptoms can include fatigue probably the result of impaired carnitine biosynthesismalaise, and inflammation of the gums [ 411 ].
As vitamin C deficiency progresses, vitamin c and cold synthesis becomes impaired and connective tissues become weakened, causing petechiae, ecchymoses, purpura, joint pain, poor wound healing, singulair and weight loss, and corkscrew hairs [ 1vitamin c and cold, 24]. Additional signs of scurvy include depression as well as swollen, bleeding gums and loosening or loss of teeth due to tissue and capillary fragility [ 689 ].
Iron deficiency anemia can also occur due to increased bleeding and decreased nonheme iron absorption secondary to low vitamin C intake [ 611 ], vitamin c and cold. In children, bone disease can be present [ 6 ]. Left untreated, scurvy is fatal [ 69 ]. Until the end of the 18 th century, many sailors who ventured on long ocean voyages, with little or no vitamin C intake, contracted or died from scurvy. During the mids, 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 [ ].
Today, vitamin C deficiency and scurvy are rare in developed countries [ 8 ]. Vitamin C deficiency is uncommon in developed countries but can still occur in people with limited food variety.
The following groups are more likely than others to be at risk of obtaining insufficient amounts of vitamin C. Studies consistently show that smokers have lower plasma and leukocyte vitamin C levels than nonsmokers, due in part 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 also decreases vitamin C levels. Although the IOM was unable to establish a specific vitamin C requirement for nonsmokers who are regularly exposed to secondhand smoke, these individuals should ensure that they meet the RDA for vitamin C [ 48 ].
Although fruits and vegetables are the best sources of vitamin C, many other foods have small amounts of this nutrient, vitamin c and cold. Thus, through a varied diet, most people should be able to meet the vitamin C RDA or at least obtain enough to prevent scurvy. People who have limited food variety—including some elderly, indigent individuals who prepare their own food; people who abuse alcohol or drugs; food faddists; people with mental illness; and, occasionally, children—might not obtain sufficient vitamin C [ 4, 11 ].
People with severe intestinal malabsorption or cachexia and some cancer patients might be at increased risk of vitamin C inadequacy [ 29 ]. Low vitamin C concentrations can also occur in patients with end-stage renal disease on chronic hemodialysis [ 30 ]. This section focuses on four diseases and disorders in which vitamin C might play a role: Epidemiologic evidence suggests that higher consumption of fruits and vegetables is associated with lower risk vitamin c and cold most types of cancer, perhaps, in part, due to their high vitamin C content [ 12 ].
Vitamin C can limit the formation of carcinogens, such as nitrosamines [ 231 ], in vivo; modulate immune response [ 24 ]; 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, stomach, oral cavity, larynx or pharynx, and esophagus [ 24 ]. Plasma concentrations of vitamin C are also lower in people with cancer than controls [ 2 ], vitamin c and cold.
However, evidence from prospective cohort studies is inconsistent, possibly due to varying intakes of vitamin C among studies, vitamin c and cold. Evidence from most randomized clinical trials suggests that vitamin C supplementation, usually in combination with other micronutrients, does not affect cancer risk. MAX study, a randomized, double-blind, vitamin c and cold, placebo-controlled clinical trial,13, healthy French adults received antioxidant supplementation with mg ascorbic acid, 30 mg vitamin E, vitamin c and cold, 6 mg beta-carotene, mcg selenium, and 20 mg zinc, or placebo [ 35 ].
After a median follow-up time of 7. In addition, baseline antioxidant status was related to cancer risk in men, but not in women [ 36 ].
In a large intervention trial conducted in Linxian, China, daily supplements of vitamin C mg plus molybdenum 30 mcg for 5—6 years did not significantly affect the risk of developing esophageal or gastric vitamin c and cold [ 39 ]. Moreover, during 10 years of follow-up, vitamin c and cold, this supplementation regimen failed to significantly affect total morbidity or mortality from esophageal, gastric, or other cancers [ 40 ].
A review of vitamin C and other antioxidant supplements for the prevention of gastrointestinal cancers found no convincing evidence that vitamin C or beta-carotene, vitamin A, or vitamin E prevents gastrointestinal cancers [ 41 ]. A similar review by Coulter and colleagues found that vitamin C supplementation, in combination with vitamin E, had no significant pubertal hormones and fat distribution changes on death risk due to cancer in healthy individuals [ 42 ].
At this time, the evidence 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 substantial limitation in interpreting many of these studies is that investigators did not measure vitamin C concentrations before or after supplementation.
Plasma and tissue concentrations of vitamin C are tightly controlled in humans. At daily intakes of mg or higher, cells appear to be saturated and at intakes of at least mg, plasma concentrations increase only marginally [ 210243339 ], vitamin c and cold. During the s, vitamin c and cold, studies by Cameron, Campbell, and Pauling suggested that high-dose vitamin C has beneficial effects on quality of life and survival time in patients with terminal cancer [ 4546 ].
However, some subsequent studies—including a randomized, double-blind, placebo-controlled clinical trial by Moertel and colleagues at the Mayo Clinic [ 47 ]—did not support these findings. The authors of a review assessing the effects of vitamin C in patients with advanced cancer concluded that vitamin C confers no significant mortality benefit [ 42 ].
Emerging research suggests that the route of vitamin C administration intravenous vs. Most intervention trials, including the one conducted by Moertel and colleagues, used only oral administration, whereas Cameron and colleagues used a combination of oral and intravenous IV administration. Concentrations of this magnitude are selectively cytotoxic to tumor cells in vitro [ 169 ].
Research in mice suggests that pharmacologic doses of IV vitamin C might show promise in treating otherwise difficult-to-treat tumors [ 51 ]. A high concentration of vitamin C may act as a pro-oxidant and generate hydrogen peroxide that has selective toxicity toward cancer cells [ ]. Based on these findings and a few case reports of patients with advanced cancers who had remarkably long survival times following administration of high-dose IV vitamin C, some researchers support reassessment of the use of high-dose IV vitamin C as a drug to treat cancer [ 34951vitamin c and cold ].
Therefore, individuals undergoing these procedures should consult with their oncologist prior to taking vitamin C or other antioxidant supplements, especially in high doses [ 56 ].
Evidence from many epidemiological studies suggests that high intakes of fruits and vegetables are associated with a reduced risk of cardiovascular disease [ 15758 ]. 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 [ 1458 ]. 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 [ 259 ].
Results from prospective studies examining associations between vitamin C intake and cardiovascular disease risk are conflicting [ 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.