The results of most earlier prospective studies indicated that low or deficient intakes of vitamin C were associated with an increased risk of cardiovascular diseases and that modest dietary intakes of about 200 mg/day were sufficient for maximum reduction of cardiovascular disease risk among non-smoking men and women (2, 74).
Coronary heart disease
Several studies had failed to find significant reductions in the risk of coronary heart disease (CHD) among vitamin C supplement users in well-nourished populations (4, 5). This might be due to saturation through their normal diet and the observation that vitamin C can only show effects in a large subpopulation with low vitamin C levels, thus potential health problems (81).
One notable exception was the epidemiological follow-up study entitled National Health and Nutrition Examination Study number one (NHANES I) (6), which found that the risk of death from cardiovascular diseases was 42% lower in men and 25% lower in women who consumed more than 50 mg/day of dietary vitamin C and who regularly took vitamin C supplements, corresponding to a total vitamin C intake of about 300 mg/day (7).
Results from the Nurses’ Health Study, based on the follow-up of more than 85,000 women over 16 years, also suggest that higher vitamin C intakes may protect the heart against atherosclerosis (8). In this study, vitamin C intakes of more than 359 mg/day from diet plus supplements or supplement use alone were associated with a 27–28% reduction in CHD risk. However, in those women who did not take vitamin C supplements, dietary vitamin C intake was not significantly associated with CHD risk.
Furthermore, a meta-analysis of nine prospective cohort studies, including more than 290,000 adults who were free of CHD at baseline and followed for an average of 10 years, found that those who took more than 700 mg/day of supplemental vitamin C had a 25% lower risk of CHD than those who did not take vitamin C supplements (9).
Data from the National Institutes of Health (NIH) indicate that plasma and circulating cells in healthy, young subjects became fully saturated with vitamin C at a dose of about 400 mg/day (10). The results of the pooled analysis of prospective cohort studies suggest that maximum reduction of CHD risk may require vitamin C intakes high enough to saturate plasma and circulating cells, and thus the vitamin C body pool (11).
Overall, it could be shown that current research suggests that vitamin C deficiency is associated with a higher risk of mortality from CHD and that vitamin C may slightly improve endothelial function and lipid profiles, especially at low plasma vitamin C levels (91).
As in many studies of vitamin C intake and cerebrovascular or cardiovascular disease risk, it is difficult to separate the effects of vitamin C on stroke risk from the effects of other components of fruits and vegetables, emphasizing the benefits of a diet rich in fruits and vegetables. In fact, blood vitamin C levels may be a good indicator (‘biomarker’) for fruit and vegetable intake and other lifestyle factors that may contribute to a reduced risk of stroke.
A 10-year prospective study in 20,649 adults found that those with the highest vitamin C concentrations in blood experienced a 42% lower risk of stroke compared to those in the lowest quartile (12).
Vitamin C plays an important role in the immune system which implies effects on clinical endpoints when faced with infections (65).
A Cochrane review showed that the preventive use of vitamin C supplementation of ≥200 mg significantly reduced the duration of episodes of common cold: In children, the duration of common cold symptoms was reduced by ~14% and in adults, it was reduced by 8%.
In addition, the review showed in a subgroup of marathon runners, skiers and soldiers training in the Arctic, doses ranging from 250 mg/day to 1 g/day decreased the incidence of colds by 50% (64).
Most of the prevention trials used a dose of 1 g/day. When treatment was started at the onset of symptoms, vitamin C supplementation neither shortened the duration nor the severity of colds in 7 placebo-controlled trials at doses ranging from 1 to 4 g/day (64).
A large number of studies have shown that increased consumption of fresh fruits and vegetables is associated with a reduced risk for most types of cancer (13).
Among the case-control studies investigating the role of vitamin C in cancer prevention, most have shown that higher intakes of vitamin C are associated with decreased incidence of cancers of the mouth, throat and vocal chords, gullet (esophagus), stomach, colorectal system, and lung.
In addition, prospective studies with less chance of bias compared to case-control studies have found significant cancer risk reductions in people consuming at least 80 to 110 mg vitamin C daily (2).
A prospective study of 870 men over a period of 25 years found that those who consumed more than 83 mg vitamin C daily had a 64% reduction in lung cancer compared with those who consumed less than 63 mg per day (14).
Although most large prospective studies found no association between breast cancer and vitamin C intake, two studies found dietary vitamin C intake to decrease breast cancer risk in certain subgroups.
In the Nurses' Health Study, premenopausal women with a family history of breast cancer who consumed an average of 205 mg/day of vitamin C from foods had a 63% lower risk of breast cancer than those who consumed an average of 70 mg/day (15). In the Swedish Mammography Cohort, women who were overweight and consumed an average of 110 mg/day of vitamin C had a 39% lower risk of breast cancer compared to overweight women who consumed an average of 31 mg/day (16).
A number of observational studies have found increased dietary vitamin C intake to be associated with decreased risk of stomach cancer, and laboratory experiments indicate that vitamin C inhibits the formation of compounds promoting cancer in the stomach (78).
Infection with the bacteria helicobacter pylori (H. pylori) is known to increase the risk of stomach cancer and also appears to lower the vitamin C content of stomach secretions. Although two intervention studies did not find a decrease in the occurrence of stomach cancer with vitamin C supplementation (17), more recent research suggests that vitamin C supplementation may be a useful addition to standard H. pylori extermination therapy in reducing the risk of gastric cancer (18).
Decreased vitamin C levels in the lens of the eye have been associated with increased severity of cataracts, occurring more frequently and becoming more severe as people age.
Some but not all studies have observed increased dietary vitamin C intake (19) and increased blood levels of vitamin C (20) to be associated with decreased risk of cataracts. Those studies that have found a relationship suggest that vitamin C intake may have to be higher than 300 mg/day for a number of years before a protective effect can be detected (2).
A 7-year controlled intervention trial of a daily antioxidant supplement containing 500 mg vitamin C, 400 IU of vitamin E, and 15 mg beta-carotene in 4,629 men and women found no difference between the antioxidant combination and a placebo on the development and progression of age-related cataracts (21).
Whereas a review showed that higher vitamin C intake and serum ascorbate might be inversely associated with risk of cataract and a vitamin C intake is advocated for the primary prevention of cataract (79).
Overall, there might be a positive relationship between vitamin C intake and the development of cataracts. Further clarification might be required before specific recommendations can be made.
Vitamin C is essential for the body to make collagen, which is a part of normal cartilage. Cartilage is destroyed in osteoarthritis, putting pressure on bones and joints. Some research suggests that free radicals may also be involved in the destruction of cartilage, and that antioxidants such as vitamin C can limit the damage caused by free radicals.
There is some evidence that people who eat diets rich in vitamin C are less likely to be diagnosed with arthritis (22). However, there is some potential for the use of vitamin C in osteoarthritis, though study results are controversial and the lack of prospective trials preclude any recommendation at this time (80).
Rheumatoid arthritis (RA) is an autoimmune disease that occurs when the body's own immune system mistakenly attacks the cell lining inside the joint. RA can cause joint pain, stiffness, swelling, and loss of joint function.
In a prospective, population-based study, lower intakes of fruit and vegetables and vitamin C were associated with an increased risk of developing RA (23). Those in the lowest category of vitamin C intake, compared with the highest, increased their risk of developing RA more than threefold.
Abnormal growth and development has been observed in infants of women exposed to lead during pregnancy, while children who are chronically exposed to lead are more likely to develop learning disabilities, behavioral problems, and to have low IQs. In adults, lead toxicity may result in kidney damage and high blood pressure.
A study of 19,578 people, including 4,214 children from 6 to 16 years of age, found higher vitamin C levels in blood to be associated with significantly lower blood lead level (24). An intervention trial that examined the effects of vitamin C supplementation on blood lead levels in 75 adult male smokers found that 1,000 mg/day of vitamin C resulted in significantly lower blood lead levels over a 4-week treatment period compared to a placebo (25). A lower dose of 200 mg/day did not significantly affect blood lead levels, despite the finding that serum vitamin C levels were not different than those of the group that took 1,000 mg/day.
The mechanism for the relationship between vitamin C intake and blood lead levels is not known, although it has been postulated that vitamin C may inhibit intestinal absorption or enhance urinary excretion of lead.
Authored by Dr Peter Engel in 2010, reviewed and revised by Dr. Volker Elste on 22.05.2017