Vitamin C is an essential micronutrient for humans, with pleiotropic functions related to its potent antioxidant and a cofactor for a family of biosynthetic and gene regulatory enzymes. Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system. Its deficiency results in impaired immunity and higher susceptibility to infections. Its use during common cold has been shown to decrease the duration of illness in some studies.
Till date, the recommended prophylactic dose for viral disease prevention is controversial. Some reviews pointed out that 100-200 mg of vitamin C proved to be adequate to optimize cell and tissue levels for the reduction of chronic disease risks. This exceeds the recommended daily allowance which is 90 mg/day for adult men and 75 mg/day for women.
100 to 200 mg of vitamin C can be easily achieved by eating a variety of food, especially fruits and vegetables.
- One large red guava: 120 mg
- One medium-sized orange:70-80 mg
- 100 gram of broccoli: 90 mg
- One Kiwi: 250 mg
- 100 gm bell peppers: 128 mg
- 100 gm Strawberry: 60 mg
- 100 gm Papaya: 60 mg
- 100 gm Tomato: 25 mg
In reference to the ongoing COVID pandemic it should be noted that there have been few anecdotal case reports where very high oral or Intravenous doses are being used for sick cases (1GM- 4GM). This sometimes misleads the public, and they start consuming Vitamin C preparations blindly as a prophylaxis for the disease which is a waste of money apart from carrying a risk of side effects.
Vitamin C intake has been a known risk factor for oxalate kidney stone formation, especially with consumption of 1000 mg or more per day. Administration above the upper level (2000 mg for adults and 400 mg for children 1-3 years old) may also cause gastrointestinal discomforts such as diarrhea, nausea, gastritis, fatigue, heartburn or insomnia.
Side effects are seen with vitamin C supplements and not to vitamin C naturally found in foods. Therefore, it is recommended to meet the nutrient requirement from natural food sources during this time.