**4.7 Other disease conditions**

A randomized factorial clinical trial from 11 centers in the US involving 3640 patients with age-related macular degeneration (AMD) and vision loss due to cataract was carried out over a follow-up period of 6.3 years [35]. The participants received antioxidants including vitamin C at a dose of 500 mg/day. The results showed no significant effect of the antioxidants on both development and progression of the diseases. However, there was no adverse effect recorded. In addition, the doses used were lower as compared to other trials. For example, an inverse relationship was found between the risk of cataract development and vitamin C intake [71, 72], with a decrease in odds at dosages greater than 102 mg/day [73].

In rare cases, some studies used very high doses of vitamin C. For example, in a prospective cohort study among 71 patients with confirmed acute and chronic allergic diseases [74], 7.5 g of vitamin C infusion (2–3 times per week) was given to the participants over a mean period of 3.2 weeks (acute) or 11.9 weeks (chronic). At the end of the treatment, there was a significant reduction in both allergy-specific and non-specific symptoms. The use of such very high doses of vitamin C was due to its well-known wide safety margin—continuous usage of vitamin C because of oxidative stress and the need to restore the already depleted pool in the patients. A review by Carr and McCall [75] revealed that high doses of vitamin C had also been used in the management of acute and chronic pain syndromes such as cancer and post-herpetic neuralgia with positive outcomes.
