Vitamin C And Immune System Pdf

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Nutrition and Immunity pp Cite as. Many factors influence whether an individual will become sick or not.

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See also: Immunity In Brief. The immune system protects the body against infection and disease. It is a complex and integrated system of cells, tissues, and organs that has specialized roles in defending against foreign substances and pathogenic microorganisms, including bacteria , viruses , and fungi. The immune system also functions to guard against the development of cancer.

For these actions, the immune system must recognize foreign invaders, as well as abnormal cells and distinguish them from self 1. However, the immune system is a double-edged sword in that host tissues can be damaged in the process of combating and destroying invading pathogens. A key component of the immediate immune response is inflammation , which can cause damage to host tissues, although the damage is usually not significant 2.

Inflammation is discussed in a separate article ; this article focuses on nutrition and immunity. Cells of the immune system originate in the bone marrow and circulate to peripheral tissues through the blood and lymph. Organs of the immune system include the thymus, spleen, and lymph nodes 3.

T- lymphocytes develop in the thymus, which is located in the chest directly above the heart. The spleen, which is located in the upper abdomen, makes antibodies and removes old and damaged red blood cells 4. The immune system is broadly divided into two major components: innate immunity and adaptive immunity. Innate immunity involves immediate, nonspecific responses to foreign invaders, while adaptive immunity requires more time to develop its complex, specific responses 1.

Innate immunity is the first line of defense against foreign substances and pathogenic microorganisms. It is an immediate, nonspecific defense that does not involve immunologic memory of pathogens.

A lack of immunologic memory means that the same response is mounted regardless of how often a specific antigen is encountered 6. The innate immune system is comprised of various anatomical barriers to infection, including physical barriers e. In addition to anatomical barriers, the innate immune system is comprised of soluble factors and phagocytic cells that form the first line of defense against pathogens. Soluble factors include the complement system , acute-phase proteins , and messenger proteins called cytokines 6.

The complement system, a biochemical network of more than 30 proteins in plasma and on cellular surfaces, is a key component of innate immunity. The complement system elicits responses that kill invading pathogens by direct lysis cell rupture or by promoting phagocytosis. Complement proteins also regulate inflammatory responses, which are part of innate immunity Acute-phase proteins are a class of plasma proteins that are important in inflammation. Cytokines secreted by immune cells in the early stages of inflammation stimulate the synthesis of acute-phase proteins in the liver Cytokines are chemical messengers that have key roles in regulating the immune response; some cytokines directly fight pathogens.

For example, some interferons have antiviral activity 6. These soluble factors are important in recruiting phagocytic cells to local areas of infection. Monocytes , macrophages , and neutrophils are key immune cells that engulf and digest invading microorganisms in the process called phagocytosis. These cells express surface receptors that identify pattern recognition receptors that are unique to pathogenic microorganisms but conserved across several families of pathogens Figure 1 2 , For more information about the innate immune response, see the article on Inflammation.

Adaptive immunity also called acquired immunity , a second line of defense against pathogens , takes several days or weeks to fully develop. However, adaptive immunity is much more complex than innate immunity because it involves antigen -specific responses and immunologic "memory. B cells produce antibodies , which are specialized proteins that recognize and bind to foreign proteins or pathogens in order to neutralize them or mark them for destruction by macrophages.

The response mediated by antibodies is called humoral immunity. In contrast, cell-mediated immunity is carried out by T cells — lymphocytes that develop in the thymus. Different subgroups of T cells have different roles in adaptive immunity. For instance, cytotoxic T cells killer T cells directly attack and kill infected cells, while helper T cells enhance the responses and thus aid in the function of other lymphocytes 5, 6. Regulatory T cells, sometimes called suppressor T cells, suppress immune responses 4.

In addition to its vital role in innate immunity, the complement system modulates adaptive immune responses and is one example of the interplay between the innate and adaptive immune systems 7 , Components of both innate and adaptive immunity interact and work together to protect the body from infection and disease. Nutritional status can modulate the actions of the immune system; therefore, the sciences of nutrition and immunology are tightly linked reviewed in In fact, malnutrition is the most common cause of immunodeficiency in the world 14 , and chronic malnutrition is a major risk factor for global morbidity and mortality More than million people are estimated to be undernourished, most in the developing world 16 , but undernutrition is also a problem in industrialized nations, especially in hospitalized individuals and the elderly Poor overall nutrition can lead to inadequate intake of energy and macronutrients , as well as deficiencies in certain micronutrients that are required for proper immune function.

Such nutrient deficiencies can result in immunosuppression and dysregulation of immune responses. In particular, deficiencies in certain nutrients can impair phagocytic function in innate immunity and adversely affect several aspects of adaptive immunity, including cytokine production, as well as antibody - and cell-mediated immunities 18, Overnutrition, a form of malnutrition where nutrients, specifically macronutrients, are provided in excess of dietary requirements, also negatively impacts immune system functions see Overnutrition and obesity.

Thus, states of malnutrition and infection can aggravate each other and lead to a vicious cycle Protein -energy malnutrition PEM; also sometimes called protein-calorie malnutrition is a common nutritional problem that principally affects young children and the elderly 20, This malnutrition stunts physical growth and mental development, with lasting effects into adulthood Clinical conditions of severe PEM are termed marasmus, kwashiorkor, or a hybrid of these two syndromes.

Marasmus is a wasting disorder that is characterized by depletion of fat stores and muscle wasting. It results from a deficiency in both protein and calories i. Individuals afflicted with marasmus appear emaciated and are grossly underweight and do not present with edema In contrast, a hallmark of kwashiorkor is the presence of edema.

Kwashiorkor is primarily caused by a deficiency in dietary protein, while overall caloric intake may be normal 23, Both forms are more common in developing nations, but certain types of PEM are also present in various subgroups in industrialized nations, such as the elderly and individuals who are hospitalized In the developed world, PEM more commonly occurs secondary to a chronic disease that interferes with nutrient metabolism, such as inflammatory bowel disease , chronic renal failure, or cancer Thus, when treating PEM in connection with chronic disease, it is necessary to address the underlying cause of malnutrition, as well as correct the associated nutrient deficits 25, Regardless of the specific cause, PEM significantly increases susceptibility to infection by adversely affecting aspects of both innate immunity and adaptive immunity With respect to innate immunity, PEM has been associated with reduced production of certain cytokines and several complement proteins, as well as impaired phagocyte function 20 , 27, Such malnutrition disorders can also compromise the integrity of mucosal barriers, increasing vulnerability to infections of the respiratory, gastrointestinal , and urinary tracts With respect to adaptive immunity, PEM primarily affects cell-mediated aspects instead of components of humoral immunity.

In particular, PEM leads to atrophy of the thymus, the organ that produces T cells, which reduces the number of circulating T cells and decreases the effectiveness of the memory response to antigens 23 , PEM also compromises functions of other lymphoid tissues, including the spleen and lymph nodes While humoral immunity is affected to a lesser extent, antibody affinity and response is generally decreased in PEM It is important to note that PEM usually occurs in combination with deficiencies in essential micronutrients , especially vitamin A, vitamin B 6 , folate, vitamin E, zinc, iron, copper, and selenium Experimental studies have shown that several types of dietary lipids fatty acids can modulate the immune response Fatty acids that have this role include the long-chain polyunsaturated fatty acids PUFAs of the omega-3 and omega-6 classes.

PUFAs are fatty acids with more than one double bond between carbons. In all omega-3 fatty acids, the first double bond is located between the third and fourth carbon atom counting from the methyl end of the fatty acid n Similarly, the first double bond in all omega-6 fatty acids is located between the sixth and seventh carbon atom from the methyl end of the fatty acid n-6 Humans lack the ability to place a double bond at the n-3 or n-6 positions of a fatty acid; therefore, fatty acids of both classes are considered essential nutrients and must be derived from the diet For more information, see the article on Essential Fatty Acids Other fatty acids in the n-3 and n-6 classes can be endogenously synthesized from ALA or LA see Figure 3 in the article on essential fatty acids.

However, synthesis of EPA and, especially, DHA may be insufficient under certain conditions, such as during pregnancy and lactation 31, Long-chain PUFAs are incorporated into membrane phospholipids of immune cells, where they modulate cell signaling of immune and inflammatory responses, such as phagocytosis and T-cell signaling.

They also modulate the production of eicosanoids and other lipid mediators Eicosanoids are carbon PUFA derivatives that play key roles in inflammatory and immune responses.

During an inflammatory response, long-chain PUFAs e. Eicosanoids derived from AA can also regulate B- and T-cell functions. To a certain extent, the relative production of these lipid mediators can be altered by dietary and supplemental intake of lipids. In those who consume a typical Western diet, the amount of AA in immune cell membranes is much greater than the amount of EPA, which results in the formation of more eicosanoids derived from AA than EPA.

However, increasing n-3 fatty acid intake dose-dependently increases the EPA content of immune cell membranes. The resulting effect would be increased production of eicosanoids derived from EPA and decreased production of eicosanoids derived from AA, leading to an overall anti-inflammatory effect 34, This is currently an active area of investigation; see the article on Essential Fatty Acids.

While n-3 PUFA supplementation may benefit individuals with inflammatory or autoimmune diseases , high n-3 PUFA intakes could possibly impair host-defense mechanisms and increase vulnerability to infectious disease 29 , Animal studies demonstrate that high dietary intake of EPA and DHA results in decreased pathogen clearance and increased susceptibility to experimental infections In humans, a small number of randomized controlled trials RCTs indicate that EPA in particular may suppress some aspects of the immune response.

Moreover, dose and participant age appear to be important modulating factors. Supplementation with 1. CLA is found naturally in meat and milk of ruminant animals, but it is also available as a dietary supplement that contains two isomers, cis -9, trans CLA and trans , cis CLA.

CLA supplementation was also associated with a decrease in levels of two pro-inflammatory cytokines and an increase in levels of an anti-inflammatory cytokine Similar effects on the immune response have been observed in some animal studies 47, 48 ; however, a few other human studies have not found beneficial effects of CLA on various measures of immune status and function More research is needed to understand the effects of CLA on the human immune response.

Further, lipids in general have a number of other roles in immunity besides being the precursors of eicosanoids and similar immune mediators. For instance, lipids are metabolized by immune cells to generate energy and are also important structural and functional components of cell membranes. Moreover, lipids can regulate gene expression through stimulation of membrane receptors or through modification of transcription factor activity.

Further, lipids can covalently modify proteins , thereby affecting their function

Vitamin C and the Immune System

Box , Christchurch , New Zealand. Vitamin C is an essential micronutrient for humans, with pleiotropic functions related to its ability to donate electrons. It is a 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. Vitamin C supports epithelial barrier function against pathogens and promotes the oxidant scavenging activity of the skin, thereby potentially protecting against environmental oxidative stress.

Open Medicine is an open access journal that provides users with free, instant, and continued access to all content worldwide. The primary goal of the journal has always been a focus on maintaining the high quality of its published content. Its mission is to facilitate the exchange of ideas between medical science researchers from different countries. Papers connected to all fields of medicine and public health are welcomed. Open Medicine accepts submissions of research articles, reviews, case reports, letters to editor and book reviews.

Vitamin C is the generic term for L-threo-hexoenono-1,4-lactone [ 6 ], which constitutes a low molecular weight carbohydrate [ 1 , 7 ]. Chemically, vitamin C is a gluconic acid lactone derived from glucuronic acid and water-soluble ketolactone with 2 ionizable hydroxyl groups with prominent antioxidant properties [ 1 , 6 ]. In nature, the 2 essential isomeric molecules of vitamin C are found in equal parts, namely the reduced form D-ascorbic acid and the chemically active and oxidized form L-ascorbic acid [ 8 ], which are mutually interchangeable [ 1 , 6 , 9 , 10 ]. Vitamin C has a strong potential to reduce distinct molecules while being reversibly oxidized to dehydroascorbic acid DHA , which can be reduced back to vitamin C exhibiting full biological activity [ 1 , 6 , 11 ]. Inside the cell, DHA is subsequently reduced to ascorbic acid [ 16 ]. Due to these characteristics, vitamin C in involved in several vital processes such as energy metabolism and gene transcription, as well as in regulation of hormonal and epigenetic pathways [ 17 ]. The natural sources of vitamin C are citrus fruits, kiwi, mango, strawberries, papaya, tomatoes, green leafy vegetables, and broccoli, for instance [ 1 , 7 , 10 , 18 — 20 ].

Vitamin C and the Immune Response in Health and Disease

See also: Immunity In Brief. The immune system protects the body against infection and disease. It is a complex and integrated system of cells, tissues, and organs that has specialized roles in defending against foreign substances and pathogenic microorganisms, including bacteria , viruses , and fungi. The immune system also functions to guard against the development of cancer.

Vitamin C also known as ascorbic acid and ascorbate is a vitamin found in various foods and sold as a dietary supplement. There is some evidence that regular use of supplements may reduce the duration of the common cold , but it does not appear to prevent infection. Vitamin C is generally well tolerated. Vitamin C was discovered in , isolated in , and, in , was the first vitamin to be chemically produced. Vitamin C is an essential nutrient for certain animals including humans.

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