Adequate intakes of micronutrients are required for the immune system to function efficiently. Micronutrient deficiency suppresses immunity by affecting innate, T cell mediated and adaptive antibody responses, leading to dysregulation of the balanced host response. This situation increases susceptibility to infections, with increased morbidity and mortality. In turn, infections aggravate micronutrient deficiencies by reducing nutrient intake, increasing losses, and interfering with utilization by altering metabolic pathways. Insufficient intake of micronutrients occurs in people with eating disorders, in smokers (active and passive), in individuals with chronic alcohol abuse, in certain diseases, during pregnancy and lactation, and in the elderly. This paper summarises the roles of selected vitamins and trace elements in immune function. Micronutrients contribute to the body's natural defences on three levels by supporting physical barriers (skin/mucosa), cellular immunity and antibody production. Vitamins A, C, E and the trace element zinc assist in enhancing the skin barrier function. The vitamins A, B6, B12, C, D, E and folic acid and the trace elements iron, zinc, copper and selenium work in synergy to support the protective activities of the immune cells. Finally, all these micronutrients, with the exception of vitamin C and iron, are essential for antibody production. Overall, inadequate intake and status of these vitamins and trace elements may lead to suppressed immunity, which predisposes to infections and aggravates malnutrition. Therefore, supplementation with these selected micronutrients can support the body's natural defence system by enhancing all three levels of immunity.
The immune system protects the body against pathogens and cancer cells, thereby defending it against infections and diseases via three main components: epithelial barriers, immune cells and proteins including antibodies. Immune defences are constantly active and consist of a complex network of coordinated biological responses. Therefore, the immune system needs to be fed properly with energy sources and essential micronutrients serving as cofactors in the development, maintenance and expression of the immune response. The general nutritional status of an individual modulates immune functions, and immunocompetence is regarded as a measure of adequate nutrition. Low levels of vitamins, minerals and trace elements lead to suppressed immunity, predisposing individuals to infections, which in turn aggravate the nutritional status, leading to a vicious cycle. Supplying the deficient micronutrients with the diet or a dietary supplement can re-establish immune function. A sufficient and balanced diet should cover the overall micronutrient requirements. However, many population segments both in developing and industrialized countries do not get adequate amounts of essential micronutrients through the diet. Current environmental and geopolitical developments (i.e. global economic crisis, rice crisis and other food shortages, the increase in maize cultivation for ethanol production, etc.) are exacerbating problems of nutritional status in many parts of the world and represent a serious threat to nutritional health. This review focuses on nutritional aspects of the immune system and discusses the roles of vitamins A, D, E, C, B6, B12 and folate as well as of the trace elements selenium, zinc, iron and copper in supporting the body's natural defence system and restoring resistance to infections by enhancing the three levels of immunity: epithelial barriers, immune cells and antibody production.
Vitamin C and zinc play important roles in nutrition, immune defence and maintenance of health. Intake of both is often inadequate, even in affluent populations. The common cold continues to place a great burden on society in terms of suffering and economic loss. After an overview of the literature on the effects of the separate administration of either vitamin C or zinc against the common cold, this article presents data from two preliminary, double-blind, randomized, placebo-controlled trials, conducted with a combination of 1000 mg vitamin C plus 10 mg zinc in patients with the common cold. In both studies, a nonsignificant reduction of rhinorrhoea duration (range 9-27%) was seen. In pooled analyses of both studies (n=94), vitamin C plus zinc was significantly more efficient than placebo at reducing rhinorrhoea over 5 days of treatment. Furthermore, symptom relief was quicker and the product was well tolerated. In view of the burden associated with the common cold, supplementation with vitamin C plus zinc may represent an efficacious measure, with a good safety profile, against this infectious viral disease.
The present paper is intended to give an overview on the roles of vitamin C and Zn in immune functions. Vitamin C concentrations in the plasma and leucocytes rapidly decline during infections and stress. Supplementation of vitamin C improves components of the human immune system such as antimicrobial and natural killer (NK) cell activities, lymphocyte proliferation, chemotaxis and delayed-type hypersensitivity. Vitamin C contributes to maintaining the redox integrity of cells and thereby protects them against reactive oxygen species generated during the respiratory burst and in the inflammatory response. Similarly, Zn deficiency impairs cellular mediators of innate immunity such as phagocytosis, NK cell activity, and the generation of oxidative burst. Thus, both nutrients play important and complementary roles in immune function and the modulation of host resistance to infectious agents, reducing the risk, severity and duration of infectious diseases. A deficiency in one of these essential nutrients weakens immunity since vitamin C is crucial for cellular immunity and Zn for the production of antibodies.A large number of randomized controlled intervention trials with intakes of £1 g vitamin C and £30 mg Zn are available. These trials show that adequate intakes of vitamin C and Zn ameliorate symptoms and shorten the duration of respiratory tract infections including the common cold. Natural defences can only provide full protection when the body has sufficient Zn, as well as high levels of vitamin C.The physiological effects of vitamin C provide clear evidence and rationale for a number of ways in which it might help to protect against infection.
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