A Powerful Ally in The Fight Against Infectious Dieseases: Nutrition

Overview of infectious diseases

The human body, which is in contact with microorganisms from birth, is temporarily or permanently colonised with a large number of microorganisms. In this process, the relationship with microorganisms may be perceived as a danger by the immune system and may cause an infection response. The infection response may damage cells and tissues and result in disease. The immune system tries to prevent and cure colonisation or infection response. In the emergence of the disease following infection, the behavioral effect of the person is very important as well as the biological characteristics of the person. Customs, manners, and customs influence people's behaviour, which also plays an important role in the transmission of infection. Behavioral characteristics such as consuming raw meat and raw milk and bathing infrequently can lead to susceptibility to infectious diseases. Respiratory tract infections and diseases transmitted by fecal contamination are common in places where hand-washing habits are low. Close personal contact such as contact of fingers exposed to microorganism contamination with the nose or eyes, shaking hands, and kissing increases the exposure time and causes the microorganism to spread rapidly. Infectious diseases often constitute a situation that concerns public health and requires urgent measures to be taken. A person with an infectious disease can also become a risk factor for other members of the society. Infectious diseases are among the most complex and variable health problems that humanity has faced throughout its history. The best example of this is COVID-19, which is not only a worldwide health crisis but also pushes the limits of societies' resistance, solidarity, and scientific progress.

Classification

The classification of infectious diseases can vary according to the type of microorganism, the symptoms, and the course of the disease and has an important role in diagnosis, treatment, or disease prevention. Types of infections can be grouped as bacterial infections, viral infections, fungal infections, or parasitic infections, according to the microorganisms that trigger the disease; respiratory tract infections, urinary tract infections, skin infections, digestive system infections, etc. according to the site of occurrence. according to the type of spread; infections can be classified as airborne, waterborne, contact, or sexually transmitted infections and, according to the duration of the disease, it is possible to classify them as acute (short-term) or chronic (long-term).Identification of the causative agent is critical in the diagnosis and treatment of infectious diseases and antimicrobial agents are used in specific treatment after the causative agent is identified. However, it should not be forgotten that antimicrobial resistance has become a serious problem today, especially due to behaviors such as irrational use of antibiotics.

Prevalence

The incidence of infectious diseases has decreased significantly in recent decades due to improved hygiene, vaccination, and antibiotic use. However, in the developing world, about one-third of deaths are still associated with infectious diseases. Some infections continue to threaten public health in developed societies due to reasons such as mass migration and remain the leading cause of death in low-income countries and a major risk for vulnerable groups such as infants and the elderly. Upper respiratory tract infections are the most common illness for which inpiduals seek medical care, and both influenza and pneumonia are still a common cause of death in the elderly. Strengthening immunisation measures therefore remains vital.

What is immunization?

Immunization is an important strategy for protection against infections. There are two types of immunization: active or passive. Active immunization stimulates the body's immune system through vaccines, while passive immunization provides temporary protection with ready-made antibodies. The effective and safe vaccines available today can protect against many serious infections. The immune system plays an important role in the susceptibility, persistence, and clearance of infections Since 70-80% of immune cells are present in the gut; there is a complex interaction between the gut microbiota, the intestinal epithelial layer, and the mucosal immune system. In addition to local mucosal immune responses in the gut, it is increasingly recognised that the gut microbiome also influences systemic immunity.

The role of gut microbiota health in the immune system

The gut microbiota regulates immune responses and provides resistance to pathogens. It is known that the composition of the microbiota is affected by various factors such as antibiotic use that can disrupt the microbiota structure and provide room for harmful microorganisms.The intestinal wall plays an important role in protection against infections. This barrier is the first defense mechanism against bacterial invasion. In addition, this barrier is reinforced by the mucus lining and is reported to act as a reservoir for antimicrobial molecules. The interaction between the gut microbiota and the intestinal epithelium leads to continuous immune signaling and the regulation of this signaling is important for intestinal homeostasis (internal balance). If this functioning system is disrupted, the risk of infection may increase.Another way in which the microbiota influences the immune response is through the formation of dietary components or microbial metabolites (end products). These metabolites have properties that support intestinal homeostasis. For example, short-chain fatty acids and tryptophan support the immune system by increasing the production of antimicrobial compounds and mucus. A reduction or loss of these metabolites can lead to imbalances in gut homeostasis and increased susceptibility to infections. Therefore, the delicate balance between gut microbiota, microbial products and host factors is an important factor influencing optimal functioning of the immune system and gut health. It is reported that an unhealthy diet is associated with an increased risk of infection due to its negative effects on the gut microbiota and may directly influence the development of some non-communicable diseases.

Nutrition in infectious diseases

Nutrition is of great importance for a healthy immune system. Adequate and balanced nutrition is essential for the healthy functioning of the immune system. Nutrients contain factors that support immune responses. Proper nutrition can reduce the risk of chronic diseases and increase the effectiveness of immune cells. In particular, it is known that nutrition affects the risk of infectious diseases in children and causes nutritional deficiencies, which have a negative impact on the immune system. Deficiencies in nutritional status can reduce the function of immune cells and increase susceptibility to infections. On the other hand, adequate intake of certain minerals and vitamins is important for protection against infections and for the formation of the immune response. In particular, the beneficial composition of breast milk can improve the immune system of the baby and reduce the severity and duration of the immune response to infections. An adequate and balanced diet in terms of all nutrients plays an important role in protection against infections and in the immune response during infectious diseases. On the other hand, changes in modern lifestyles can increase the severity of infections and the risk of developing diseases.It is important to consume fruits and vegetables rich in antioxidant vitamins such as vitamins A and C, which have immune-boosting properties. Vitamin E is also effective in strengthening the immune system. Vitamin D also plays an important role in the immune system. Plenty of fluid intake is required to stabilize body temperature. Overnutrition can promote the accumulation of excess body fat and obesity, which contributes to a chronic inflammatory state that coincides with immune disorders. Prioritising efforts to optimise nutrient intake is a good approach to reducing disease burden and improving preparedness.

Macronutrients in the immune response

Carbohydrates make up a large part of a healthy diet. Carbohydrate types with a low glycaemic index can support the immune system. It is known that the energy requirement increases by 10% for each 1°C of increased body temperature during infection. During an infectious disease, an increase in energy requirement is observed due to increased body temperature. Carbohydrates support meeting the energy need. In addition, carbohydrate sources such as whole grains and their products with high dietary fibre content should be included more due to their contribution to microbiota health, while simple sugar consumption should be restricted by reducing added sugars. Protein consists of amino acids, which are the basic building blocks in the body. These amino acids are essential for satiety, energy metabolism, bone health and immune function. The daily protein requirement of a healthy adult is 0.8 g/kg/day and low protein intake may have negative effects on lean body mass, muscle function and immune system. Proteins are necessary for the construction of cells that support the immune system and have stimulatory effects. Among proteins, lactoferrin is considered to support innate immunity and is the primary defense mechanism against infections and acts by maturing T cells and scavenging reactive oxygen species. Whey protein contains high-quality protein and increases immunity by stimulating immune cells. It is therefore critical to maintain protein balance during illness. Different types of dietary fats can reduce or exacerbate infection. It is known that arachidonic acid, eicosapentaenoic acid (EPA), and other fatty acids show different activities in the body, especially arachidonic acid has effects that increase the infection response and other fatty acids have effects that reduce infection. It is known that saturated fatty acids have negative effects on the immune system, and high-fat diets negatively affect the gut-associated immune response. Omega-3 fatty acids positively affect the immune response, weaken the infection status and provide immune resistance. Increasing the consumption of omega-3 source oily fish may be the right strategy to improve the immune system.

Micronutrients in the immune response

Adequate intake of micronutrients such as vitamins C and D and zinc is important for the proper functioning of the immune system. Micronutrients interact with each other and even a deficiency of a single nutrient can negatively affect the immune system. In addition to dietary intake of these micronutrients, taking them as supplements can also have an effect on the immune system. In particular, taking nutrients such as vitamin D and zinc as supplements can regulate immune function. Retinoic acid, the active form of vitamin A, increases the levels of protective IgA antigens, especially against viral infections, by suppressing cells that increase the infection response and antibody production. Vitamin A deficiency leads to impairment in the behaviour of T and B immune cells. Vitamin D is a fat-soluble vitamin produced in the skin as a result of contact with sunlight. Vitamin D receptors are present in more than thirty tissues and are involved in the regulation of immune functions, cell proliferation and differentiation. It suppresses the increase of cells that cause an increase in infection. Care should be taken to keep serum vitamin D levels in the optimal range in healthy inpiduals. It should be recommended that serum vitamin D monitoring should be included in routine examinations. Vitamin E is a fat-soluble antioxidant vitamin found in the cell membrane of all cells. Vitamin E shows radical scavenging activity. Immune cells also contain high amounts of vitamin E, which protects them from oxidative damage due to high metabolic activity. Vitamin E especially protects the function of T cells. Studies indicate that vitamin E is effective on infections. Iron transports oxygen from the lungs to the cells, is involved in the production of red blood cells, leukocyte production, the production of various enzymes and the immune system. Adequate iron levels are important for immune functions, including the differentiation and proliferation of T lymphocytes and their ability to kill pathogens. In the presence of infection, pathogens start to increase using iron and can damage the immune system. Therefore, iron homeostasis needs to be kept under constant control. Iron supplementation in case of infection is a very inappropriate strategy. Various organ meats, red meat, legumes, oilseeds, green leafy vegetables, and enriched breakfast cereals are rich sources of iron in the diet. However, considering the absorption of iron, the richest source is red meat. Zinc is important for the development and functioning of immune cells. Zinc is more effective on T lymphocytes in the immune system. In addition, zinc is an essential mineral for the functioning and development of neutrophils and natural killer cells, and in this way, it is also necessary for the development and functioning of innate immune cells. Under normal physiological conditions, every cell maintains and controls the zinc balance. However, a possible deficiency can lead to allergies, infections, and autoimmune diseases. As a result, an adequate diet in terms of all micronutrients and macronutrients ensures a correct immune response.

Increased fluid need during infectious diseases

One of the responses caused by the infection in the body is increased body temperature. It is necessary to consume plenty of fluids to keep the temperature balanced. Adequate fluid intake is extremely important in removing harmful elements from the body, ensuring the continuity of functions and carrying out many biochemical reactions in the body. Therefore, 2-2.5 liters of only water should be drunk every day. Beverages such as herbal teas and tea should not be included in the total fluid intake. It should not be forgotten that these drinks cause water loss in the body (diuretic effect).

Breast milk

Breast milk is the safest and cleanest food source and contains antibodies that protect against infections. Breast milk, which is the only source of energy and nutrients in the first months of life, is dynamic. Colostrum, which is the milk secreted in the first days after birth, is not only a rich source of nutrients for the baby, but also protects against infections with its high level of immunoglobulins (Ig). Lactoferrin in breast milk has a wide antimicrobial and antiviral effect and is considered an immunomodulatory protein. Lactoperoxidase in breast milk also shows antimicrobial activity. Casein constitutes 40% of breast milk proteins. Casein has a natural immune effect on the stomach. Oligosaccharides, which are complex carbohydrate structures, are reported to have antipathogenic, immunomodulatory, anti-inflammatory, and prebiotic effects. Breast milk is a living fluid and contains macrophages, stem cells, and lymphocytes. 1010 breast milk-derived lymphocytes are passed to the baby per day. Due to all these beneficial contents of breast milk, it has important effects on childhood, adult health, and maternal health. It can reduce the risk of a range of diseases from lower and upper respiratory tract infections to obesity in childhood. Studies have shown that breastfed babies show a decrease in hospital visits due to infections. Breast milk also forms the baby's gut microbiome with the bacteria it contains and modulates the immune system. Therefore, breast milk provides an important advantage in terms of protection against infections. However, in some cases, breastfeeding may be inappropriate; for example, HIV, herpes, Ebola

Functional foods

Garlic has beneficial effects on health. Allicin is a compound in garlic that reduces the release of factors that increase the infection response. Garlic supplements support the immune system through T cells and stimulate natural killer cells. It is stated that allicin, which is considered the main biological component of garlic, has strong antimicrobial effects. Turmeric contains curcumin. Curcumin has been proven to suppress the production of cells that increase the infection response. Curcumin has anti-inflammatory, antioxidant, and antiviral effects. Propolis, a resinous material produced by honey bees, is widely consumed as an immune system booster. It is used due to its antibacterial, antifungal, antiviral, antiparasitic, liver protective, and immunomodulatory activities. It has strong anti-inflammatory and immunomodulatory effects.

Misconceptions

The use of vitamin D does not prevent the diseases. Monitoring vitamin D levels ensures the proper functioning of the immune system. It is not appropriate to take iron supplements during the infectious disease process. Continuity of adequate and balanced nutrition should be ensured instead of taking a loaded supplement after the disease is caught.

The human body is in lifelong contact with microorganisms from birth, sometimes these microorganisms can cause disease. Infections can become a serious problem, often affecting public health. The immune system protects the organism against infections and this system interacts with nutrition. Optimal nutrition, including breastfeeding during infancy, can increase resistance to infections and has a positive effect on the immune system.The inclusion of various functional foods with antioxidant, antimicrobial, and anti-inflammatory properties in the diet is a strategy that can strengthen immunity. While consuming a diet that meets energy demands and provides essential nutrients promotes a healthy immune system, both under and overnutrition have been associated with immune dysfunction. Prioritizing efforts to optimize nutrient intake is one approach to reduce disease burden and improve preparedness.