Vitamins C, D and Zinc: Synergistic Roles in Immune Function and Infections

Abstract

The immune system is a complex and sophisticated network of specialized tissues, organs, cells, proteins, and chemicals which has evolved in order to protect the host from a range of dangerous agents such as bacteria, virus, fungi, and parasites. There is a close relationship between nutritional status and immune function. Hence, immunocompetence can be regarded as a measure of adequate nutrition. Inter-individual variations in many immune functions exist within the normal healthy population and are due to age, genetics, gender, ethnic background, socio-economic situation, diet, stress, habitual levels of exercise, alcohol consumption, smoking habits, etc. In addition, seasonal and temperature changes as well as being in crowded spaces (e.g., while commuting in public means of transportation, or working in open space offices) pose an additional burden on the immune system. Among the essential micronutrients required to support a normal immune function, vitamin C, vitamin D and the mineral zinc play a central role. Through their complementary and synergistic effects, they support components of both innate and adaptive immunity which comprise epithelial barriers, cellular defense and antibodies constituting the three main lines of immune defense. Furthermore, vitamin C, D and zinc are actively used by cells of the immune system engaged in fighting infections like upper respiratory tract infections and a state of micronutrient deficiency can arise during severe infections. Here we review the literature on the immune supportive properties of vitamins C, D and zinc and the impact of their supplementation in reducing the incidence or ameliorating symptoms of upper respiratory tract infections, which are among the most common infections in humans. Finally, we discuss their relevance in situations known to challenge the immune system such as exposure to temperature changes, to pollutants, or being in crowded spaces which serve as mixers where pathogens can stay suspended and transfer from host to host thereby increasing the risk of spreading infectious diseases because of close contact and long exposure.