Vitamin C has been shown to be beneficial for people with certain diseases or conditions. High intakes of vitamin C have been associated with decreased risk of heart disease, cancer, eye diseases, and neurological conditions. High dose vitamin C, with an upper tolerable level set at 2 grams per day set by the USDA has been shown to be safe. This limit was set by the USDA due to gastrointestinal side effects. Among healthy individuals, the recommended daily intake of vitamin C is 75 mg for women and 90 mg for men. (27)
Combinations of vitamins, minerals, and cancer:
Ten-year follow-up results from the General Population Trial, a study conducted in in Linxian, China from 1985 to 1991 that gave daily vitamin and mineral supplements (50 microg selenium, 30 mg vitamin E, and 15 mg beta-carotene) to 29,584 adults at high risk of esophageal and stomach cancers were presented. In the original study, researchers had found that treatment led to a decrease in mortality from all causes, cancer overall, and gastric cancer. Adding to these important findings, post-intervention follow-up indicated that the beneficial effects of the beta-carotene–vitamin E–selenium combination in the General Population Trial remained evident up to 10 years after the intervention. Cumulative mortality decreased from 33.62% to 32.19% and cumulative gastric cancer mortality decreased from 4.28% to 3.84%. These benefits were consistently greater in participants who were younger (<55 y) at the beginning of the intervention. (28)