What does vitamin Cdo?
Vitamin C is a water-soluble vitamin that has a number of biological functions.
Acting as an antioxidant, one of vitamin C’s important functions is to protect LDL cholesterol from oxidative damage. (Only when LDL is damaged does cholesterol appear to lead to heart disease, and vitamin C may be one of the most important antioxidant protectors of LDL.)1 Vitamin C may also protect against heart disease by reducing the stiffness of arteries and the tendency of platelets to clump together.2
The antioxidant properties of vitamin C are thought to protect smokers, as well as people exposed to secondhand smoke, from the harmful effects of free radicals. A controlled trial demonstrated the ability of 3 grams of vitamin C, taken by nonsmokers two hours prior to being exposed to cigarette smoke, to reduce the free radical damage and LDL cholesterol oxidation associated with exposure to cigarette smoke.3 The smoke-induced decline in total antioxidant defense was also diminished. These beneficial effects were not observed in nonsmokers under normal conditions (no free radical exposure).
Vitamin C is needed to make collagen, the "glue" that strengthens many parts of the body, such as muscles and blood vessels. Vitamin C also plays important roles in wound healing and as a natural antihistamine. This vitamin also aids in the formation of liver bile and helps to fight viruses and to detoxify alcohol and other substances.
Recently, researchers have shown that vitamin C improves nitric oxide activity.4 Nitric oxide is needed for the dilation of blood vessels, potentially important in lowering blood pressure and preventing spasms of arteries in the heart that might otherwise lead to heart attacks. Vitamin C has reversed dysfunction of cells lining blood vessels.5 The normalization of the functioning of these cells may be linked to prevention of heart disease.
Evidence indicates that vitamin C levels in the eye decrease with age6 and that supplementing with vitamin C prevents this decrease,7 possibly leading to a lower risk of developing cataracts.8 9 Healthy people have been reported in some, but not all, studies10 to be more likely to take vitamin C and vitamin E supplements than are people with cataracts.11
Vitamin C has been reported to reduce activity of the enzyme, aldose reductase, in people.12 Aldose reductase is the enzyme responsible for accumulation of sorbitol in eyes, nerves, and kidneys of people with diabetes. This accumulation is believed to be responsible for deterioration of these parts of the body associated with diabetes. Therefore, interference with the activity of aldose reductase theoretically helps protect people with diabetes.
Vitamin C may help protect the body against accumulation or retention of the toxic mineral, lead. In one preliminary study, people with higher blood levels of vitamin C had much lower risk of having excessive blood levels of lead.13 In a controlled trial, male smokers with moderate to high levels of lead received supplements of 1,000 mg per day of vitamin C, 200 mg per day of vitamin C, or a placebo.14 Only those people taking 1,000 mg per day of vitamin C experienced a drop in the blood lead levels, but the reduction in this group was dramatic.
People with recurrent boils (furunculosis) may have defects in white blood cell function that are correctable with vitamin C supplementation. A preliminary study of people with recurrent boils and defective white blood cell function, found that 1 gram of vitamin C taken daily for four to six weeks, resulted in normalization of white blood cell function.15 Ten of twelve people receiving vitamin C became symptom-free within one month and remained so for periods of one to three years without additional supplementation. The other two people required long-term vitamin C supplementation to prevent recurrences.
A double-blind trial found that 500 mg of vitamin C per day for one year reduced the risk of developing reflex sympathetic dystrophy (a painful nerve condition of the extremities), after a wrist fracture.16
In a small, preliminary trial, vitamin C (500 mg twice daily) combined with rutoside (500 mg twice daily), a derivative of the flavonoid, rutin, produced marked improvement in three women with progressive pigmented purpura (PPP), a mild skin condition.17 Although not a serious medical condition, cosmetic concerns lead people with PPP to seek treatment with a variety of drugs. The vitamin C/rutoside combination represents a promising, non-toxic alternative to these drug treatments, but larger, controlled trials are needed to confirm these preliminary results.
Where is vitamin c found?
Broccoli, red peppers, currants, Brussels sprouts, parsley, potatoes, citrus fruit, and strawberries are good sources of vitamin C.
Vitamin C has been used in connection with the following conditions
Who is likely to be deficient of vitamin c?
People with kidney failure have an increased risk of vitamin C deficiency.20 However, people with kidney failure should take vitamin C only under the supervision of a doctor.
How much vitamin c is usually taken?
Some scientists have recommended that healthy people take multi-gram amounts of vitamin C for the prevention of illness. However, little or no research supports this point of view and it remains controversial. Supplementing more results in an excretion level virtually identical to intake, meaning that consuming more vitamin C does not increase the amount that remains in the body.23 On the basis of extensive analysis of published vitamin C studies, researchers at the Linus Pauling Institute at Oregon State University have called for the RDA to be increased, but only to 120 mg.24 This same report reveals that “. . . 90–100 mg vitamin C per day is required for optimum reduction of chronic disease risk in nonsmoking men and women.” Thus, the multiple gram amounts of vitamin C taken by many healthy people may be superfluous.
The studies that ascertained approximately 120–200 mg daily of vitamin C is correct for prevention purposes in healthy people have typically not investigated whether people suffering from various diseases can benefit from larger amounts. In the case of the common cold, a review of published trials found that amounts of 2 grams per day in children appear to be more effective than 1 gram per day in adults, suggesting that large intakes of vitamin C may be more effective than smaller amounts, at least for this condition.25
Are there any side effects or interactions with vitamin c?
It is widely (and mistakenly) believed that mothers who consume large amounts of vitamin C during pregnancy are at risk of giving birth to an infant with a higher-than-normal requirement for the vitamin. The concern is that the infant could suffer “rebound scurvy,” a vitamin C deficiency caused by not having this increased need met. Even some medical textbooks have subscribed to this theory.29 In fact, however, the concept of “rebound scurvy” in infants is supported by extremely weak evidence.30 Since the publication in 1965 of the report upon which this mistaken notion is based, millions of women have consumed high amounts of vitamin C during pregnancy and not a single new case of rebound scurvy has been reported.31
A preliminary study found that people who took 500 mg per day of vitamin C supplements for one year had a greater increase in wall thickness of the carotid arteries (vessels in the neck that supply blood to the brain) than those who did not take vitamin C.32 Thickness of carotid artery walls is an indicator of progression of atherosclerosis. Currently, no evidence supports a cause-and-effect relationship for the outcome reported in this study. The vast preponderance of research suggests either a protective or therapeutic effect of vitamin C for heart disease, or no effect at all.
People with the following conditions should consult their doctor before supplementing with vitamin C: glucose-6-phosphate dehydrogenase deficiency, iron overload (hemosiderosis or hemochromatosis), history of kidney stones, or kidney failure.
It has been suggested that people who form calcium oxalate kidney stones should avoid vitamin C supplements, because vitamin C can be converted into oxalate and increase urinary oxalate.33 34 Initially, these concerns were questioned because of potential errors in the laboratory measurement of oxalate.35 36 However, using newer methodology that rules out this problem, recent evidence shows that as little as 1 gram of vitamin C per day can increase the urinary oxalate levels in some people, even those without a history of kidney stones.37 38 In one case, 8 grams per day of vitamin C led to dramatic increases in urinary oxalate excretion and kidney stone crystal formation causing bloody urine.39 People with a history of kidney stones should consult a doctor before taking large amounts (1 gram or more per day) of supplemental vitamin C.
Despite possible therapeutic effects of vitamin C in people with diabetes at lower intakes, one case of increased blood sugar levels was reported after taking 4.5 grams per day.40
Are there any drug interactions?