Vitamin C is a potent antioxidant and contributes to the body's innate and adaptive immune system by supporting various cellular functions. Vitamin C supports epithelial barrier function against pathogens and potentially protects against environmental oxidative stress by promoting oxidant scavenging activity of the skin.
Studies suggest that taking multiple smaller doses of vitamin C, as opposed to single larger doses significantly improves absorption. Levels of vitamin C in the blood rise steeply with doses up to 200mg per day. Above this level, the proportion of absorbed vitamin C progressively decreases. For example, the fraction of vitamin C absorbed decreases from up to 90% at lower doses (e.g. less than 200mg) to around 50% absorption at doses above 1g per day.
Our intestines do have a limited ability to absorb vitamin C which is why absorption decreases to less than 50% when taking amounts greater than 1000mg in one sitting. Once the body's tissues have become saturated with Vitamin C, absorption decreases and any excess is then excreted in urine. Generally speaking, mega-doses of vitamin C in healthy adults is not toxic due to effective elimination processes.
Where did the idea of mega-dosing of vitamin C come from? It originated in the 1970s by Linus Pauling who was a Nobel Laureate and a self-proclaimed champion of Vitamin C who promoted mega-doses of vitamin C daily as a way to prevent colds and chronic diseases. The equivalent of his mega-doses were the amount of 12-24 oranges. Whilst mega-dosing is not uncommon, it is important to understand what the optimal dose is to keep you healthy.
The bottom line is that the maximum benefit from vitamin C is achieved when taking multiple smaller doses (e.g. 250mg twice per day), rather than higher single doses, and taking doses of vitamin C above 1g per dose is of questionable benefit. Scientific studies have demonstrated that regular use of vitamin C supplements at doses of 250mg to 1000mg daily can assist in reducing the duration and severity of common cold symptoms. Based on what is known about absorption, we recommend taking at least 250mg twice per day (this is the recommended dosing schedule for IMUNI Immune Defence).
1. Nutrient Reference Values for Australia and New Zealand. Link: https://www.nrv.gov.au/nutrients/vitamin-c
2. NIH Office of Dietary Supplements: Vitamin C. Link: https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional
3. Carr A. 2017. Vitamin C and Immune Function. Nutrients Journal. Available from: https://pubmed.ncbi.nlm.nih.gov/29099763/
4. Vitamin C. Harvard T.H. Chan: School of Public Health. Available from: : https://hsph.harvard.edu/nutritionsource/vitamin-c/