Content
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Vitamin D: Fundamentals and functions
- 1.1 Chemical structure and form of vitamin D (D2 and D3)
- 1.2 mechanisms for the synthesis of vitamin D in the skin under the influence of UV radiation
- 1.3 Alternative sources of vitamin D: food and dietary supplement products
- 1.4 Vitamin D metabolism: Stages of activation in the liver and kidneys
- 1.5 Vitamin D (VDR) receptors and their distribution in the body
- 1.6 Genomic and non -agenomic mechanisms of vitamin D action
- 1.7 The role of vitamin D in the regulation of calcium and phosphorus metabolism
- 1.8 The effect of vitamin D on bone health and osteoporosis prevention
- 1.9 Other functions of vitamin D: effect on the muscles, nervous system and cardiovascular system
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Vitamin D and immunity: scientific data
- 2.1 Immune system: brief review (congenital and acquired immunity)
- 2.2 The effect of vitamin D on cells of congenital immunity (macrophages, neutrophils, dendritic cells)
- 2.3 Regulation of the expression of antimicrobial peptides under the influence of vitamin D
- 2.4 The effect of vitamin D on cells of acquired immunity (T-lymphocytes, b-lymphocytes)
- 2.5 The role of vitamin D in the regulation of the cytokine storm and inflammatory reactions
- 2.6 Vitamin D and autoimmune diseases: pathogenetic aspects
- 2.7 Studies on the effect of vitamin D on the prevention and treatment of infectious diseases (SARS, influenza, tuberculosis, COVID-19)
- 2.8 Clinical studies: the relationship between vitamin D level and the risk of infectious diseases
- 2.9 meta-analyzes and systematic reviews about the effect of vitamin D on immunity
- 2.10 The influence of vitamin D on vaccination: Strengthening the immune response
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Vitamin D: causes, symptoms and diagnosis
- 3.1 risk factors for vitamin D (geographical position, seasonality, age, skin, obesity, disease)
- 3.2 Symptoms of vitamin D deficiency in adults and children (fatigue, weakness, bones and muscles, frequent infections)
- 3.3 Methods for diagnosing vitamin D: blood test for 25 (OH) D
- 3.4 Interpretation of the results of the analysis on vitamin D: determination of optimal levels
- 3.5 Classification of vitamin D deficiency: deficiency, deficiency, severe deficiency
- 3.6 influence of vitamin D deficiency on immune function and exposure to infections
- 3.7 The consequences of a prolonged deficiency of vitamin D: Health risks (osteoporosis, autoimmune diseases, cardiovascular diseases)
- 3.8 deficiency of vitamin D in pregnant women and nursing women: risks for mother and child
- 3.9 Vitamin D deficiency in older people: features and consequences
- 3.10 Vitamin D deficiency in people with chronic diseases: interconnection and influence on the course of the disease
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Vitamin D dietary supplements: types, dosage and use
- 4.1 forms of vitamin D in dietary supplements: d2 (ergocalciferol) and d3 (cholecalciferol)
- 4.2 Advantages and disadvantages of various forms of vitamin D (D2 VS D3)
- 4.3 fat -soluble and water -soluble forms of vitamin D: features of assimilation
- 4.4 dosages of vitamin D in dietary supplements: preventive and therapeutic doses
- 4.5 Recommendations for vitamin D dosages for different age groups and categories of the population (children, adults, elderly, pregnant, nursing)
- 4.6 safe upper levels of vitamin D consumption
- 4.7 Factors affecting the absorption of vitamin D from dietary supplements (gastrointestinal tract, concomitant diseases, taking other drugs)
- 4.8 Interaction of vitamin D with other vitamins and minerals (calcium, vitamin K2)
- 4.9 Recommendations for choosing dietary supplements with vitamin D: Quality and safety criteria
- 4.10 Review of popular dietary supplements with vitamin D in the market: Comparison and analysis of compositions
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Clinical recommendations for the use of vitamin D to maintain immunity
- 5.1 Target groups for the preventive administration of vitamin D (risk groups of deficiency)
- 5.2 Schemes of the preventive administration of vitamin D (seasonal reception, year -round reception)
- 5.3 The role of vitamin D in the complex therapy of infectious diseases
- 5.4 Vitamin D and prevention of SARS and influenza: evidence
- 5.5 Vitamin D and COVID-19: Recent studies and recommendations
- 5.6 Individual approach to the purpose of vitamin D: Accounting for related diseases and drug therapy
- 5.7 Monitoring the level of vitamin D during the reception of dietary supplements
- 5.8 Dose correction of vitamin D depending on the level of 25 (OH) D in the blood
- 5.9 Recommendations for power to increase vitamin D (products rich in vitamin D)
- 5.10 The importance of solar exposure for the synthesis of vitamin D: Recommendations for safe tanning
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Vitamin D and autoimmune diseases: prospects for therapy
- 6.1 Autoimmune diseases: pathogenesis and the role of the immune system
- 6.2 The role of vitamin D in the regulation of an immune response in autoimmune diseases
- 6.3 Studies on the effect of vitamin D on the course of multiple sclerosis
- 6.4 Vitamin D and rheumatoid arthritis: clinical data
- 6.5 The influence of vitamin D on the course of systemic lupus erythematosus
- 6.6 Vitamin D and autoimmune thyroiditis (Hashimoto disease)
- 6.7 Studies on the effect of vitamin D on other autoimmune diseases (psoriasis, inflammatory intestinal diseases)
- 6.8 Prospects for the use of vitamin D in the complex therapy of autoimmune diseases
- 6.9 The need for further research to determine the optimal doses and schemes for the use of vitamin D for autoimmune diseases
- 6.10 Causes and contraindications to the use of high doses of vitamin D for autoimmune diseases
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Vitamin D and children’s health: Features of application
- 7.1 The role of vitamin D in the development of the bone system in children
- 7.2 Prevention of rickets using vitamin D
- 7.3 dosage of vitamin D for children of different ages (newborn, infants, older children)
- 7.4 Ways to introduce vitamin D to children (drops, solutions, tablets)
- 7.5 Vitamin D and immunity in children: Prevention of infectious diseases
- 7.6 Studies on the influence of vitamin D on the prevention of SARS in children
- 7.7 Vitamin D and atopic dermatitis in children: Clinical data
- 7.8 The effect of vitamin D on the development of allergic diseases in children
- 7.9 Symptoms of an overdose of vitamin D in children: how to avoid
- 7.10 Recommendations for the use of vitamin D in children with special needs (premature babies, children with chronic diseases)
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Hypervitaminosis D: causes, symptoms and treatment
- 8.1 causes of hypervitaminosis D: excessive dietary supplements, genetic factors
- 8.2 Symptoms of hypervitaminosis D: nausea, vomiting, weakness, hypercalcemia
- 8.3 Diagnosis of hypervitaminosis D: blood test for vitamin D and calcium
- 8.4 The consequences of hypervitaminosis D: calcification of soft tissues, kidney damage
- 8.5 Treatment of hypervitaminosis D: lifting vitamin D, low calcium diet, taking drugs that reduce blood calcium levels
- 8.6 Prevention of hypervitaminosis D: compliance with the recommended dosages of vitamin D, control of vitamin D in the blood
- 8.7 Hypervitaminosis D in children: Features and consequences
- 8.8 The effect of hypervitaminosis D on the cardiovascular system
- 8.9 Hypervitaminosis D and pregnancy: risks for mother and fetus
- 8.10 Rare forms of hypervitaminosis D: associated with genetic mutations
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Interaction of vitamin D with drugs and other dietary supplements
- 9.1 The effect of vitamin D on the metabolism of drugs
- 9.2 drugs that reduce vitamin D levels in the blood (glucocorticosteroids, antifungal drugs, anticonvulsants)
- 9.3 Vitamin D and anticoagulants: effect on blood coagulation
- 9.4 Interaction of vitamin D with drugs for the treatment of cardiovascular diseases
- 9.5 Vitamin D and hormonal therapy: Features of application
- 9.6 The influence of vitamin D on the assimilation of other vitamins and minerals (calcium, magnesium, vitamin K2)
- 9.7 Vitamin D and statins: influence on cholesterol level
- 9.8 Interaction of vitamin D with drugs for the treatment of osteoporosis
- 9.9 Recommendations for the joint administration of vitamin D with other drugs and dietary supplements
- 9.10 The need to consult a doctor before taking vitamin D in the presence of chronic diseases and medication
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Prospects for vitamin D studies and immunity
- 10.1 new areas of studies of vitamin D and immune system
- 10.2 Study of the effect of vitamin D on the prevention and treatment of chronic diseases
- 10.3 Development of new forms of vitamin D with improved bioavailability
- 10.4 Studies on the effect of vitamin D on the intestinal microbia and immunity
- 10.5 Personalized approach to the purpose of vitamin D based on genetic factors
- 10.6 Study of the role of vitamin D in the prevention and treatment of cancer
- 10.7 Studies on the influence of vitamin D on aging and life expectancy
- 10.8 New clinical studies on the use of vitamin D for autoimmune diseases
- 10.9 Development of new methods for diagnosing vitamin D deficiency
- 10.10 Integration of vitamin D into comprehensive programs for the strengthening of health and prevention of diseases
1. Vitamin D: Fundamentals and functions
- 1.1 Chemical structure and form of vitamin D (D2 and D3)
Vitamin D is a group of fat -soluble runners with a similar chemical structure based on the core of steroid. The main forms of vitamin D are vitamin D2 (ergocalciferol) and vitamin D3 (cholelciferol). They differ in the structure of the side chain of the molecule. Vitamin D2 is formed in plants and mushrooms under the influence of ultraviolet radiation from ergosterol. Vitamin D3 is synthesized in the skin of humans and animals from 7-dehydrocholesterol under the influence of ultraviolet rays of spectrum B (UVB). Despite the similarity, D2 and D3 have some differences in metabolism and effectiveness. D3, as a rule, is considered more effective in increasing the level of 25 (OH) D in the blood (the main metabolite of vitamin D used to assess its status in the body) and maintain it at the optimal level.
- 1.2 mechanisms for the synthesis of vitamin D in the skin under the influence of UV radiation
The synthesis of vitamin D3 in the skin is a complex photochemical process. The 7-dehydrocholesterol, present in the skin cells (keratinocytes), under the influence of UVB ray with a wavelength of 290-315 nm, is converted into previtamin D3. This process requires sufficient intensity and duration of UV exposure. Previtamin D3 is unstable and is quickly isolated into vitamin D3. Vitamin D3 then enters the bloodstream and binds to vitamin D-binding protein (VDBP), which transports it to the liver for further metabolism. The effectiveness of the synthesis of vitamin D3 in the skin depends on many factors, including the season, time of day, geographical latitude, height above sea level, cloudiness, air pollution, the use of sunscreens, skin color and age. Melanin, a pigment that determines the color of the skin, absorbs the UV radiation, reducing the effectiveness of the synthesis of vitamin D3 in people with dark skin. With age, the content of 7-dehydrocholesterol in the skin decreases, which also reduces the synthesis of vitamin D3.
- 1.3 Alternative sources of vitamin D: food and dietary supplement products
In addition to the synthesis in the skin, vitamin D can be obtained from food and dietary supplements. Vitamin D food sources are limited. The main sources are fatty fish (salmon, mackerel, herring, tuna), fish oil, egg yolks (especially from chickens that received food enriched with vitamin D), beef liver and some mushrooms (for example, Shiitaka), grown under UV respect. However, even with a balanced diet, the content of vitamin D in food is often not enough to maintain the optimal level in the body, especially in conditions of insufficient solar effects. Bades (biologically active additives) are an important source of vitamin D, especially for people living in regions with low insolation, having dark skin, elderly people, pregnant women and nursing women, as well as people with diseases affecting the assimilation of vitamin D. Bades are available in various forms, including tablets, capsules, chewing sweets, fluids and sprays. It is important to choose dietary supplements from reliable manufacturers that guarantee the quality and accuracy of the dosage.
- 1.4 Vitamin D metabolism: Stages of activation in the liver and kidneys
Vitamin D obtained from leather, food or dietary supplements is biologically inactive. In order for him to have his own effect, he must pass two stages of hydroxylation. The first stage takes place in the liver, where vitamin D under the influence of the 25-hydroxylase enzyme (CYP2R1) turns into 25-hydroxyvitamin D [25(OH)D]also known as calciol. 25 (OH) D is the main form of vitamin D, circulating in the blood, and is used to assess the status of vitamin D in the body. The second stage of hydroxylation occurs in the kidneys, where 25 (OH) D, under the influence of an enzyme 1-alpha-hydroxylase (CYP27B1), turns into 1.25-dihydroxyvitamin D [1,25(OH)2D]also known as calcitriol. Calcitriol is a biologically active form of vitamin D, which binds to vitamin D (VDR) receptors and has its effect on various organs and tissues. The activity of 1-alpha-hydroxylase in the kidneys is regulated by various factors, including the level of parathyroid hormone (PTH), calcium and phosphorus in the blood.
- 1.5 Vitamin D (VDR) receptors and their distribution in the body
Vitamin D (VDR) receptors are intracellular receptors belonging to the super -family of nuclear receptors. They are located in cell nuclei and are associated with 1.25 (OH) 2D (calcitriol), forming a complex, which then interacts with DNA and regulates the expression of genes. VDR is expressed in many tissues and cells of the body, including bones, intestines, kidneys, immune cells (T-lymphocytes, B lymphocytes, macrophages, dendritic cells), brain, heart, muscles, skin, pancreas and reproductive organs. VDR widespread in the body explains the diverse functions of vitamin D, including the regulation of calcium and phosphorus metabolism, maintaining bone health, modulation of the immune response, regulation of cellular growth and differentiation, as well as the effect on the cardiovascular system, the nervous system and the endocrine system.
- 1.6 Genomic and non -agenomic mechanisms of vitamin D action
Vitamin D has its effect on the body through two main mechanisms: genomic and non -agenomic. The genomic mechanism is the main mechanism of vitamin D, which includes connecting 1.25 (OH) 2D with VDR, the formation of a complex, which then interacts with DNA and regulates the expression of genes. This process takes a relatively long time (from several hours to several days) and leads to a change in protein synthesis. A non -gene mechanism is a faster vitamin D action mechanism that does not require interaction with DNA. It includes the binding of 1.25 (OH) 2D with VDR located on the cell membrane, or with other membrane receptors, which leads to the activation of various signaling ways and rapid changes in the cell function (for example, changes in the concentration of calcium inside the cell). Both vitamin D mechanisms are important for maintaining the health and normal functioning of the body.
- 1.7 The role of vitamin D in the regulation of calcium and phosphorus metabolism
The main role of vitamin D is the regulation of calcium and phosphorus metabolism, which is necessary to maintain bone health and normal function of muscles, nervous system and other organs. Vitamin D increases the absorption of calcium and phosphorus in the intestines, stimulating the synthesis of calcium-binding protein (kalbindin) in the intestinal cells. It also promotes the reabsorption of calcium and phosphorus in the kidneys, reducing their excretion in the urine. In addition, vitamin D interacts with parathyroid hormone (PTG), which regulates the level of calcium in the blood. With a low level of calcium in the blood, PTH stimulates the synthesis of 1.25 (OH) 2D in the kidneys, which leads to an increase in the absorption of calcium in the intestines and reabsorption of calcium in the kidneys. In bones, vitamin D stimulates the activity of osteoclasts (cells that destroy bone tissue), which leads to the release of calcium and phosphorus into the blood. However, in general, vitamin D promotes bone mineralization, ensuring the flow of calcium and phosphorus into bone tissue.
- 1.8 The effect of vitamin D on bone health and osteoporosis prevention
A sufficient level of vitamin D is necessary to maintain bone health throughout life. Vitamin D deficiency leads to a decrease in calcium absorption in the intestines, which can lead to osteomination (softening of bones) in adults and rickets in children. Osteoporosis is a disease characterized by a decrease in bone density and an increased risk of fractures. Vitamin D deficiency is one of the risk factors for the development of osteoporosis. The intake of vitamin D in combination with calcium can reduce the risk of fractures in older people, especially those who have a deficiency of vitamin D. Recommendations for the prevention of osteoporosis include maintaining an adequate level of vitamin D and calcium, regular physical exercises with a bone load (for example, walking, running, dancing and excessive alcohol consumption.
- 1.9 Other functions of vitamin D: effect on the muscles, nervous system and cardiovascular system
In addition to the regulation of calcium and phosphorus metabolism and maintenance of bones, vitamin D plays an important role in the functioning of other organs and systems. Muscles: Vitamin D is necessary for the normal function of muscles. Vitamin D deficiency can lead to muscle weakness, muscles (myalgia) and increased risk of falls. Nervous system: VDR is expressed in the brain, and vitamin D plays a role in the development and functioning of the nervous system. Vitamin D deficiency can be associated with an increased risk of depression, cognitive impairment and Alzheimer’s disease. Cardiovascular system: Vitamin D affects the function of the cardiovascular system, regulating blood pressure, inflammation and endothelial function (inner vascular membrane). Vitamin D deficiency can be associated with an increased risk of developing hypertension, heart failure and other cardiovascular diseases. Vitamin D also plays a role in the regulation of the immune response, cellular growth and differentiation, as well as in maintaining the health of the skin.
2. Vitamin D and immunity: scientific data
- 2.1 Immune system: brief review (congenital and acquired immunity)
The immune system is a complex network of cells, tissues and organs that protects the body from pathogens, such as bacteria, viruses, fungi and parasites, as well as abnormal cells (for example, cancer cells). The immune system is divided into two main parts: congenital immunity and acquired immunity. Inborn immunity – This is the first line of protection of the body that reacts quickly and nonspecific to the invasion of pathogens. It includes physical barriers (leather, mucous membranes), cells (macrophages, neutrophils, dendritic cells, natural killers) and molecules (complement, cytokines). Acquired immunity – This is a more complex and specific protection system that develops over time in response to contact with antigens (molecules recognized by the immune system). It includes T-lymphocytes and B lymphocytes that recognize specific antigens and produce antibodies to neutralize them. Congenital and acquired immunity work together to ensure effective protection of the body from infections and other threats.
- 2.2 The effect of vitamin D on cells of congenital immunity (macrophages, neutrophils, dendritic cells)
Vitamin D plays an important role in the regulation of the function of cellular immunity cells. Macrophages: Vitamin D activates macrophages, increasing their ability to phagocytosis (absorption and destruction of pathogens) and the production of antimicrobial peptides (for example, Katelicidin). It also modulates the production of cytokines by macrophages, reducing the products of pro-inflammatory cytokines (for example, TNF-α, IL-6) and increasing the products of anti-inflammatory cytokines (for example, IL-10). Neutrophils: Vitamin D stimulates chemotaxis neutrophils (directed movement towards the focus of infection) and increases their ability to phagocytosis and the formation of active oxygen forms (AFC) necessary for the destruction of pathogens. Dendritic cells: Vitamin D affects the ripening and function of dendritic cells, which play a key role in activating the acquired immunity. It inhibits the ripening of dendritic cells and reduces their ability to develop pro -inflammatory cytokines, which can contribute to antigens tolerance and prevent autoimmune reactions.
- 2.3 Regulation of the expression of antimicrobial peptides under the influence of vitamin D
One of the important mechanisms by which vitamin D strengthens the immunity is the regulation of the expression of antimicrobial peptides (AMP). AMP is small proteins with a wide range of antimicrobial activity against bacteria, viruses, fungi and parasites. Vitamin D stimulates the expression of the Katelicidin gene (CAMP), which encodes AMP, which plays an important role in protection against infections. Katelicidin has a direct antimicrobial effect, destroying the membranes of bacteria and viruses. It also activates other immune cells and promotes wound healing. The expression of Katelicidine is regulated by vitamin D through VDR. When binding 1.25 (OH) 2D with VDR, the CAMP gene is activated and the synthesis of the catelicidine is increased. Vitamin D deficiency can lead to a decrease in the expression of Katelicidine and increased susceptibility to infections.
- 2.4 The effect of vitamin D on cells of acquired immunity (T-lymphocytes, b-lymphocytes)
Vitamin D also affects the function of cells of acquired immunity, T-lymphocytes and B lymphocytes. T-lymphocytes: Vitamin D regulates the differentiation of T-lymphocytes and modulates their function. It inhibits the proliferation of T-Helper type 1, which are involved in the development of autoimmune diseases, and stimulates the proliferation of T-Helper type 2 (Th2), which play a role in allergic reactions and protection from parasites. Vitamin D also stimulates the development of regulatory T cells (Treg), which suppress the immune response and prevent autoimmune reactions. B-lymphocytes: Vitamin D inhibits the proliferation and differentiation of b-lymphocytes, and also reduces the production of antibodies by them. This can help reduce autoimmune reactions.
- 2.5 The role of vitamin D in the regulation of the cytokine storm and inflammatory reactions
A cytokine storm is an excessive and uncontrolled production of cytokines, which can occur in severe infections, autoimmune diseases and other conditions. A cytokine storm can lead to severe damage to organs and tissues, including lungs, heart and kidneys. Vitamin D plays a role in the regulation of the cytokine storm, modulating the production of cytokines with immune cells. It reduces the products of pro-inflammatory cytokines (for example, TNF-α, IL-6, IL-1) and increases the products of anti-inflammatory cytokines (for example, IL-10). Due to its anti-inflammatory properties, vitamin D can help prevent or soften the cytokine storm in severe infections, such as Covid-19.
- 2.6 Vitamin D and autoimmune diseases: pathogenetic aspects
Autoimmune diseases are a group of diseases in which the immune system attacks its own tissues and organs of the body. Vitamin D deficiency is associated with an increased risk of developing autoimmune diseases, such as multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, autoimmune thyroiditis and inflammatory intestinal diseases. Vitamin D plays a role in the pathogenesis of autoimmune diseases, modulating the immune response and preventing auto -aggression. He inhibits the proliferation of Th1 cells, stimulates the proliferation of Treg cells and reduces the production of autoantibodies. Vitamin D intake can help reduce the activity of autoimmune diseases and improve the quality of life of patients.
- 2.7 Studies on the effect of vitamin D on the prevention and treatment of infectious diseases (SARS, influenza, tuberculosis, COVID-19)
Numerous studies have shown that vitamin D plays a role in the prevention and treatment of infectious diseases. SARS and flu: Vitamin D deficiency is associated with an increased risk of development of acute respiratory viral infections and influenza. Vitamin D intake can help reduce the risk of infection with SARS and influenza, as well as soften the symptoms of the disease and reduce its duration. Tuberculosis: Vitamin D plays a role in the activation of macrophages that participate in the destruction of mycobacterium tuberculosis. Vitamin D deficiency is associated with an increased risk of tuberculosis. Covid-19: Several studies have shown that vitamin D deficiency is associated with an increased risk of infection Covid-19, a more severe course of the disease and increased mortality. Vitamin D intake can help reduce the risk of covid-19 infection, soften the symptoms of the disease and reduce the risk of serious complications. However, further studies are necessary to confirm the effectiveness of vitamin D in the prevention and treatment of infectious diseases.
- 2.8 Clinical studies: the relationship between vitamin D level and the risk of infectious diseases
Numerous clinical studies studied the relationship between vitamin D levels in the blood and the risk of infectious diseases. In general, these studies show that people with a higher level of vitamin D have a lower risk of developing infectious diseases, especially respiratory infections. However, the results of the studies are not always unambiguous, and some studies did not find the relationship between vitamin D level and the risk of infectious diseases. This may be due to the differences in the design of research, vitamin D dosages, the duration of vitamin D, as well as with the presence of other factors affecting the immune system.
- 2.9 meta-analyzes and systematic reviews about the effect of vitamin D on immunity
Met-analyzes and systematic reviews combine the results of several studies to obtain a more accurate assessment of the effect of vitamin D for immunity. Some metaminations and systematic reviews have shown that vitamin D reduces the risk of respiratory infections, especially in people with vitamin D deficiency. Other metaminas and systematic reviews did not find a significant vitamin D effect on the risk of infectious diseases. Further meta analyzes and systematic reviews with the inclusion of better studies are needed to obtain more convincing evidence of vitamin D efficiency in strengthening immunity.
- 2.10 The influence of vitamin D on vaccination: Strengthening the immune response
Some studies have shown that vitamin D can enhance the immune response to vaccination. Vaccination is the introduction of an antigen (for example, a weakened virus or bacteria) to stimulate an immune response and the formation of immunity to a specific disease. Vitamin D can enhance the immune response to vaccination, increasing the production of antibodies and activation of T-lymphocytes. In particular, some studies have shown that vitamin D intake is improving the immune response to flu and hepatitis B vaccination and hepatitis B. However, further studies are necessary to confirm the effectiveness of vitamin D in increasing the immune response to various vaccines.
3. Vitamin D: causes, symptoms and diagnosis
- 3.1 risk factors for vitamin D (geographical position, seasonality, age, skin, obesity, disease)
Vitamin D deficiency is a common phenomenon around the world. There are many risk factors that can contribute to the development of vitamin D deficiency: Geographical position: People living in regions with high latitude, where sunlight falls at a lesser angle, have a lesser opportunity to synthesize vitamin D in the skin, especially in the winter months. Seasonality: The synthesis of vitamin D in the skin decreases in the winter months, when there is less sunlight and people spend more time in the room. Age: With age, the ability of the skin to synthesize vitamin D decreases.