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Vitamin C
Assessment and Plan: Vitamin C
High intakes of vitamin C have been associated with lower risk of heart disease, cancer, eye diseases, and neurological conditions. High dose vitamin C, with an upper tolerable level set at 2g, has been shown to be safe. Among healthy individuals, the recommended daily intake of vitamin C is 75 mg for women and 90 mg for men. (18)
An average vitamin C intake of 46 mg per day is required to prevent scurvy (21), a deficiency state of vitamin C resulting in weakness, anemia, bruising of the skin and gum disease.
A vitamin C supplement intake of over 2 grams per day is poorly tolerated, may not be safe and results in gastrointestinal side effects. High doses of up to 18 grams per day did not result in significantly higher blood vitamin C levels. (6)
There is evidence that vitamin C intake has a benefit in lowering mortality risk for men but not in women. Men with low ascorbate blood concentrations compared with higher concentrations showed a 57% higher total mortality risk and a 62% higher cancer mortality risk. No change in risk of mortality was found with levels between 28.4 to 73.8 micromol/L. The vitamin C intake corresponding to the higher risk of mortality in men was less than or equal to 60 mg per day. (7)
Carr and Frei recommended a higher vitamin C intake of 90-100 mg per day to avoid chronic diseases. These authors expressed similar to findings as Loria, CM et al which were that low intake of vitamin C was related to an increase in cancer mortality. Carr and Frei had a different conclusion than Loria et al in that intake of vitamin C was inversely related to cancer mortality in elderly women but not in men. They also found prospective studies which demonstrated that a low vitamin C poses a higher risk of cardiovascular disease. (21)
Intravenous vitamin C results in significantly higher blood levels than oral doses, appears to damage cancer cells, but not healthy cells and may provide survival benefit in cancer patients (6). It may also improve physical function, emotional well-being, cognitive ability, and may result in lower rates of fatigue, nausea, vomiting, pain, and anorexia in cancer patients (8).
Higher intakes of dietary vitamin C from fruits and vegetables was positively and significantly associated with a higher forced expiratory volume in 1 second (FEV1) (1,2,3), an important measure of lung function for patients with asthma and bronchitis patients as well as in smokers, healthy adults and children. The degree of improvement in lung function in the research above is a range between 1-5%.
It is difficult to separate out whether this improvement in lung function is related to vitamin C itself or related to overall nutrient content contained within the fruit. One study found that the improvement in higher (forced expiratory volume in 1 second) FEV1 was positively linked with the frequency of fresh fruits, green vegetables, and salad consumption but was not associated with vitamin C levels in the blood (3).
A study which followed over 18,000 children found that those who consumed 5 servings of fruit rich in vitamin C per week were less likely to have respiratory-related health problems including wheezing, shortness of breath, or night coughing compared with those who never ate fruit with the greatest benefit seen in children with asthma. Those eating the most citrus and kiwifruit (5-7 servings per week) had 44% less incidence of wheezing compared to children eating the least (less than once a week). Shortness of breath was reduced by 32%, severe wheeze by 41%, night time cough by 27%, chronic cough by 25%, and runny nose by 28%. (4)
A supplement containing vitamin A (30,000 IU per day), vitamin C (1 gram per day), and vitamin E (70 mg per day taken for about 18 months showed a significant reduction in colonic adenoma recurrence (5).
Patients on dialysis and chronic kidney disease are at high risk for vitamin C deficiency and are recommended to have a daily intake of 60 mg of ascorbate (vitamin C). A dose of 1-1.5g of orally administered vitamin C per week is acceptable. (11)
Vitamin C has been reported to be associated with pre-eclampsia when levels of this vitamin are low (12).
For patients with iron deficiency anemia, administration of vitamin C is useful to enhance the absorption of dietary iron in the gut (13).
Vitamin C, 500 mg along with vitamin E, 400 IU; beta carotene, 15 mg; and zinc, 80 mg as zinc oxide with 2 mg of cupric oxide reduced the risk of age-related macular degeneration progression (14).
A review of 30 prevention trials showed that vitamin C, 1g daily slightly shortened cold duration—by 8% in adults and 18% in children. A review of 6 trials found that vitamin C at 200 to 2000 mg per day was even more effective for subjects in extreme conditions, such as marathon runners, which cut their risk of a contracting a cold by about half. (15)
Clinical research has demonstrated reductions in antiretroviral levels in patients taking vitamin C. (17)
Despite many positive findings in vitamin C research, the U.S. Preventive Services Task Force (USPSTF), determined that there is insufficient evidence to recommend for or against the use of vitamin C for the prevention of cancer or cardiovascular disease. (19)
