During infections and stress, vitamin C concentrations in the plasma and leukocytes, also known as white blood cells, start declining rapidly. Vitamin C supplementation was observed to improve the components of the immune system in humans such as natural killer cell and antimicrobial activities, chemotaxis, lymphocyte proliferation and delayed-type hypersensitivity. Supplementation of vitamin C also contributes to maintain the redox integrity of cells and thus provides protection against reactive oxygen species that are generated during the respiratory eruption and in the inflammatory response.

 Similarly, under nutrition of zinc or deficiency of zinc has also shown to damage the cellular mediators of innate immunity for example phagocytosis, natural killer cell activity and the generation of oxidative burst. Consequently, both these nutrients play an important role in immune function and the modulation of host resistance to infectious mediators. These nutrients reduce the risk, severity, and also the duration of infectious diseases. These nutrients are of special significance in populations in whom there is insufficient intake of them. Insufficient intake or deficiency of zinc and vitamin C is seen in the developing countries such as in low- and middle-income countries, but can also be seen in elderly populations in industrialized countries. A number of randomized controlled intervention trials with consumptions of up to 1 g of vitamin C and of 30 mg of zinc are existing. These randomized trials have documented that adequate intakes of vitamin C and zinc can improve symptoms and reduce the duration of respiratory tract infections counting the common cold too.

Additionally, vitamin C and zinc supplementation can reduce the occurrence and improve the outcome of pneumonia and malaria. It also reduces the diarrhoea infections, especially in children of developing countries.

Source: Wintergerst ES, Maggini S, Hornig DH. Immune-enhancing role of vitamin C and zinc and effect on clinical conditions. Ann Nutr Metab. 2006; 50(2):85-94. doi:10.1159/000090495