Vitamin A for children: impact on vision and immunity

Chapter 1: Fundamentals of Vitamin A and its role in the child’s body

1. 1 What is vitamin A?

Vitamin A is a fat -soluble vitamin that is critical for many physiological processes in the human body, especially during the period of growth and development of the child. It exists in two main forms: retinol (an active form contained in animal products) and carotenoids (provitamins A contained in plant foods that the body transforms into retinol). Beta-carotene is the most famous and studied carotenoid.

1. 2 Forms of vitamin A:

   • Retinol: The active form of vitamin A, quickly absorbed by the body. Contained in the liver, dairy products, eggs and fish.
   • Retinal: The aldehyde form of vitamin A participating in the visual cycle.
   • Retinic acid: An important form of vitamin A, which regulates the expression of genes and cell differentiation.
   • Carotinoids (Provitamin a): Beta-carotene, alpha-carotene and beta-crippoxantin are plant pigments that the body can convert into retinol. Contained in carrots, pumpkin, sweet potatoes, spinach and other fruits and vegetables.

2. 3 The main functions of vitamin A in the body of the child:

   • Vision: Vitamin A plays a key role in the functioning of the retina, especially in low light conditions. It is a component of rhodopsin, a photosensitive pigment necessary for night vision. Vitamin A deficiency can lead to nictalopia (chicken blindness) and other serious vision problems.
   • Immune system: Vitamin A supports the integrity of the mucous membranes, which are the first barrier of infections. It also participates in the development and functioning of immune cells, such as T-lymphocytes and B-lymphocytes necessary to combat pathogens.
   • Growth and development: Vitamin A is necessary for the normal growth and development of bones, teeth and other tissues. It regulates the expression of genes involved in cell differentiation and proliferation.
   • Health of the skin and mucous membranes: Vitamin A supports the health of the skin and mucous membranes, protecting them from dryness, inflammation and infections. It stimulates the production of mucin, a moisturizing substance that helps maintain the integrity of the mucous membranes.
   • Reproductive function: Vitamin A plays an important role in reproductive function in both men and women. It is necessary for the normal development of the embryo and maintaining the health of reproductive organs.

3. 4 Metabolism and storage of vitamin A:

After consuming vitamin A (in the form of retinol or carotenoids), it is absorbed in the small intestine and transported to the liver. The liver is the main storage of vitamin A, if necessary, vitamin A is released from the liver and transported to the blood, where it is associated with retinol-binding protein (RBP) and transstitin (TTR) to be delivered to various tissues and organs.

1. 5 Factors affecting the assimilation of vitamin A:

   • Fat content in food: Vitamin A is fat -soluble, therefore, for its optimal assimilation, it is necessary to consume it along with products containing fat.
   • Intestinal health: Intestinal diseases, such as celiac disease and Crohn’s disease, can violate the absorption of vitamin A.
   • Zinc Deficit: Zinc is necessary for the synthesis of RBP, a protein that transports vitamin A in the blood. Zinc deficiency can worsen the absorption and transportation of vitamin A.
   • Age: In newborns and young children, the assimilation of vitamin A can be less effective than in adults.
   • Interaction with other nutrients: Some nutrients, such as vitamin E and vitamin C, can improve the absorption and use of vitamin A.

Chapter 2: The influence of vitamin A on the vision of children

2. 1 The role of vitamin A is in the visual cycle:

Vitamin A plays a key role in the visual cycle, a process that allows us to see in conditions of various illumination. Retinal, the aldehyde form of vitamin A, binds to the OPSIN protein in the retina, forming rhodopsin. Rhodopsin is a photosensitive pigment that breaks down under the influence of light, sending nerve impulses to the brain that are interpreted as vision. In conditions of low illumination, Rhodopsin plays a particularly important role, allowing us to see in the dark.

2. 2 Nicatalopia (chicken blindness) and vitamin A deficiency:

Nicatalopia, or chicken of blindness, is one of the first signs of vitamin A deficiency with vitamin A deficiency, the body cannot produce a sufficient amount of rhodopsin, which leads to a deterioration in vision in low light conditions. A child with nickthalopia may experience difficulties when moving at dusk, in poorly lit rooms or at night.

2. 3 Xerophthalmia: a progressive deficiency of vitamin A and its consequences:

Xerophthalmia is a serious eye disease caused by a prolonged and pronounced deficiency of vitamin A. It is characterized by the progressive dryness of the cornea and conjunctiva, which can lead to irreversible damage to the eyes and blindness.

*   **Стадии ксерофтальмии:**

    *   **Ксероз конъюнктивы (X1A):** Сухость и сморщивание конъюнктивы.
    *   **Пятна Бито (X1B):** Белые или сероватые бляшки на конъюнктиве, состоящие из кератина, бактерий и клеточного детрита.
    *   **Ксероз роговицы (X2):** Сухость и помутнение роговицы.
    *   **Кератомаляция (X3A):** Размягчение и разрушение роговицы.
    *   **Кератомаляция с изъязвлением (X3B):** Изъязвление роговицы, которое может привести к перфорации.
    *   **Рубцы роговицы (XS):** Рубцы на роговице, возникающие после заживления язв, приводящие к ухудшению зрения.
    *   **Ксерофтальмия, связанная с системным дефицитом витамина А (XF):** Ксерофтальмия, возникающая на фоне системных заболеваний, таких как мальабсорбция.

2. 4 Diagnosis of vitamin A deficiency and its effect on vision:

Diagnosis of vitamin A deficiency includes:

*   **Осмотр глаз:** Оценка состояния конъюнктивы и роговицы для выявления признаков ксерофтальмии.
*   **Оценка ночного зрения:** Проверка способности видеть в условиях низкой освещенности.
*   **Анализ крови на уровень витамина А (ретинола):** Определение уровня ретинола в сыворотке крови. Однако уровень ретинола в крови может не всегда отражать истинные запасы витамина А в организме, особенно при хроническом дефиците.
*   **Тест на относительную дозу ретинола (RDR):** Оценка изменения уровня ретинола в крови после приема небольшой дозы витамина А. Этот тест может быть более чувствительным, чем измерение уровня ретинола в сыворотке крови.
*   **Оценка факторов риска:** Оценка диеты, истории болезни и других факторов, которые могут повысить риск дефицита витамина А.

2. 5 Treatment and prevention of vision problems associated with vitamin A deficiency:

   • Vitamin A additives: Reception of vitamin A additives in the form of retinol palmitate or retinol acetate. The dosage depends on the age, severity of the deficiency and the presence of other diseases. It is important to be careful not to exceed the recommended dose, since an overdose of vitamin A can be toxic.
   • Improvement: An increase in the consumption of products rich in vitamin A, such as liver, dairy products, eggs, carrots, pumpkin, sweet potatoes and spinach.
   • Treatment of concomitant diseases: Treatment of diseases that can violate the absorption of vitamin A, such as celiac disease and Crohn’s disease.
   • Prevention of vitamin A deficiency: Providing sufficient consumption of vitamin A with food or additives, especially in risk groups, such as children with insufficient nutrition and children with chronic diseases.
   • Vaccinating by Core: Cores are one of the main causes of vitamin A deficiency in children. Core vaccination helps to prevent this complication.
   • Enrichment of food: Enrichment of food, such as vegetable oil, vitamin A, can be an effective way to prevent vitamin A deficiency in large groups of the population.

Chapter 3: The influence of vitamin A on the immunity of children

3. 1 Vitamin A and the barrier function of the mucous membranes:

Vitamin A plays an important role in maintaining the integrity and functioning of the mucous membranes, which are the first barrier of protection against infections. The mucous membranes lift the respiratory tract, the gastrointestinal tract, the genitourinary system and the eyes. Vitamin A contributes to the differentiation and proliferation of epithelial cells that make up the mucous membranes. It also stimulates the production of mucin, a moisturizing substance that helps maintain the integrity of the mucous membranes and prevents their drying and damage. Vitamin A deficiency can lead to thinning and damage to the mucous membranes, which increases the risk of infections.

3. 2 Vitamin A and cellular immunity:

Vitamin A plays an important role in the development and functioning of cells of the immune system, such as T-lymphocytes and B-lymphocytes. T-lymphocytes are involved in cellular immunity, destroying infected cells and regulating the immune response. B-lymphocytes produce antibodies that neutralize pathogens. Vitamin A contributes to the differentiation of T-lymphocytes to various subtypes, such as T-highpers and cytotoxic T-lymphocytes. It also stimulates the production of cytokines, signal molecules that regulate the immune response. Vitamin A deficiency can lead to a violation of the functioning of T-lymphocytes and B-lymphocytes, which reduces the body’s ability to fight infections.

3. 3 Vitamin A and humoral immunity:

Vitamin and also affects humoral immunity, which is provided by antibodies produced by B-lymphocytes. Vitamin A contributes to the differentiation of B-lymphocytes into plasma cells that produce antibodies. It also stimulates the production of antibodies such as IgG, IgA and IGM, which neutralize pathogens and provide protection against infections. Vitamin A deficiency can reduce antibody production, which increases susceptibility to infections.

3. 4 Vitamin A and inflammation:

Vitamin A plays an important role in the regulation of an inflammatory response. It can have both pro -inflammatory and anti -inflammatory effects, depending on the context. In some cases, vitamin A can enhance the inflammatory response to help the body fight infection. In other cases, vitamin A can suppress an inflammatory response to prevent tissue damage. Retinic acid, the active form of vitamin A can be associated with nuclear receptors such as RAR and RXR, and regulate the expression of genes involved in inflammation.

3. 5 The effect of vitamin A deficiency on susceptibility to infections:

Vitamin A deficiency increases susceptibility to various infections, such as respiratory infections, diarrhea and measles. Children with vitamin A deficiency are more likely to suffer and have a more severe course of infections. They are also more susceptible to complications, such as pneumonia and encephalitis. Vitamin deficiency and can also increase the risk of mortality from infections.

3. 6 Clinical studies on the influence of vitamin A on the immunity of children:

Numerous clinical studies have shown that the addition of vitamin A to children with vitamin A deficiency can reduce the risk of infections and mortality. For example, studies have shown that the addition of vitamin A to children with measles can reduce the risk of complications and mortality. Other studies have shown that the addition of vitamin A to children with diarrhea can reduce the duration of the disease and reduce the risk of repeated infections.

3. 7 Vitamin A and vaccination:

Vitamin A can strengthen the immune response to vaccines. Studies have shown that the addition of vitamin A during vaccination can increase antibodies and improve infections. For example, studies have shown that the addition of vitamin A to children during measles vaccination can increase antibody production and improve measles protection.

Chapter 4: Sources of vitamin A in the nutrition of children

4. 1 Animal products rich in retinol (active form of vitamin A):

   • Liver: The liver is the richest source of retinol.
   • Dairy products: Milk, cheese and butter contain retinol.
   • Eggs: Egg yolk contains retinol.
   • Fish: Fat fish, such as salmon, tuna and herring, contains retinol.
   • Fish oil: Fish oil is a great source of retinol.

5. 2 Plant products rich in carotenoids (Provitamin A):

   • Carrot: Carrots are one of the most famous sources of beta-carotene.
   • Pumpkin: The pumpkin contains a lot of beta carotene.
   • Sweet potato: Sweet potatoes are a good source of beta-carotene.
   • Spinach: Spinach contains beta-carotene and other carotenoids.
   • Broccoli: Broccoli contains beta-carotene and other carotenoids.
   • Red pepper: Red pepper contains beta-carotene and other carotenoids.
   • Mango: Mango contains beta-carotene and other carotenoids.
   • Apricots: Apricots contain beta-carotene and other carotenoids.

6. 3 Recommendations for vitamin A consumption for children of different age groups:

   • 0-6 months: 400 μg RAE (retinol equivalent) per day.
   • 7-12 months: 500 mcg rae per day.
   • 1-3 years: 300 mcg rae per day.
   • 4-8 years: 400 mcg rae per day.
   • 9-13 years: 600 mcg rae per day.
   • 14-18 years: 900 μg RAE per day for boys and 700 mcg RAE per day for girls.

7. 4 Tips for the inclusion of products rich in vitamin A, in the diet of the child:

   • Include a variety of products in the diet rich in vitamin A: Offer a child a variety of fruits, vegetables and animal products to ensure sufficient consumption of vitamin A.
   • Cook products rich in carotenoids with the addition of fat: Carotinoids are better absorbed when they are used with fat. For example, add a little olive oil to a carrot or spinach salad.
   • Make mashed potatoes and smoothies: If it is difficult for a child to eat fruits and vegetables, try to make mashed potatoes or smoothies. Add a little yogurt or milk to improve vitamin A.
   • Add vegetables to dishes: Add grated carrots or spinach to soups, sauces and casseroles.
   • Make vegetable snacks: Offer your child chopped carrots, cucumbers and pepper as a snack.
   • Serve fruits and vegetables of bright colors: Fruits and vegetables of bright colors, such as carrots, pumpkin and sweet potatoes, usually contain more carotenoids.
   • Be patient: It may take time that the child is used to new products. Offer them again and again until he starts to eat them.

8. 5 When are the additives of vitamin A for children?

Vitamin A supplements can be necessary in the following cases:

*   **Дефицит витамина А:** Если у ребенка диагностирован дефицит витамина А, врач может назначить добавки витамина А.
*   **Мальабсорбция:** Если у ребенка есть заболевания, которые нарушают усвоение витамина А, такие как целиакия и болезнь Крона, врач может назначить добавки витамина А.
*   **Недостаточное питание:** Если ребенок не получает достаточно витамина А с пищей, врач может назначить добавки витамина А.
*   **Корь:** Детям с корью рекомендуется принимать добавки витамина А, чтобы снизить риск осложнений и смертности.

It is important to consult a doctor before taking vitamin A additives to determine the correct dosage and avoid an overdose.

Chapter 5: overdose of vitamin A and its consequences for children

5. 1 Acute toxicity of vitamin A:

Acute toxicity of vitamin A occurs when taking very high doses of vitamin A for a short period of time. Symptoms of acute toxicity of vitamin A include:

*   **Тошнота и рвота**
*   **Головная боль**
*   **Головокружение**
*   **Раздражительность**
*   **Сонливость**
*   **Нарушение зрения**
*   **Повышение внутричерепного давления**
*   **Судороги**
*   **Кома**

5. 2 Chronic toxicity of vitamin A:

Chronic toxicity of vitamin A occurs when taking moderately high doses of vitamin A for a long period of time. Symptoms of chronic toxicity of vitamin A include:

*   **Сухость и шелушение кожи**
*   **Выпадение волос**
*   **Боли в костях и суставах**
*   **Увеличение печени и селезенки**
*   **Повышение уровня печеночных ферментов**
*   **Анорексия**
*   **Усталость**
*   **Раздражительность**
*   **Повышение внутричерепного давления**
*   **Отек диска зрительного нерва**
*   **Кровотечения**
*   **Врожденные дефекты у новорожденных (если беременная женщина принимала высокие дозы витамина А)**

5. 3 Factors that increase the risk of vitamin A overdose:

   • Reception of high doses of vitamin A additives: Vitamin A additives contain concentrated doses of vitamin A, which can easily lead to an overdose.
   • Simultaneous intake of several additives containing vitamin A: Some multivitamins and other additives also contain vitamin A. With the simultaneous use of several such additives, the risk of an overdose increases.
   • The use of a large number of products rich in vitamin A: The use of a large amount of liver and other products rich in vitamin A can lead to an overdose, especially if the additives of vitamin A.
   • Disorders of the liver function: People with impaired liver function are more susceptible to the toxicity of vitamin A, since the liver plays an important role in metabolism and storage of vitamin A.
   • Pregnancy: Pregnant women should observe special caution in relation to vitamin A, since high doses of vitamin A can cause congenital defects in newborns.

6. 4 Diagnosis of an overdose of vitamin A:

Diagnosis of vitamin A overdose includes:

*   **Сбор анамнеза:** Оценка симптомов и истории приема витамина А.
*   **Физический осмотр:** Оценка признаков токсичности витамина А, таких как сухость кожи, выпадение волос и боли в костях.
*   **Анализ крови на уровень витамина А (ретинола):** Определение уровня ретинола в сыворотке крови. Высокий уровень ретинола в крови может указывать на передозировку витамина А.
*   **Анализ печеночных ферментов:** Оценка уровня печеночных ферментов. Повышенный уровень печеночных ферментов может указывать на повреждение печени, вызванное токсичностью витамина А.
*   **Рентгенография костей:** Оценка состояния костей. Изменения в костях могут быть признаком хронической токсичности витамина А.

5. 5 Treatment of an overdose of vitamin A:

Treatment of vitamin A overdose includes:

*   **Прекращение приема витамина А:** Самое главное – немедленно прекратить прием витамина А.
*   **Симптоматическое лечение:** Лечение симптомов, таких как тошнота, рвота, головная боль и боли в костях.
*   **Поддерживающая терапия:** В тяжелых случаях может потребоваться госпитализация и поддерживающая терапия, такая как внутривенное введение жидкости и контроль за функцией печени.
*   **Прием активированного угля:** Активированный уголь может помочь адсорбировать витамин А в желудочно-кишечном тракте и предотвратить его дальнейшее всасывание.

5. 6 Prevention of an overdose of vitamin A:

   • Do not exceed the recommended dose of vitamin A: Observe the recommended dose of vitamin A for your age and health.
   • Consult a doctor before taking the additives of vitamin A: Consult a doctor to make sure that you really need vitamin A additives and what dosage is safe for you.
   • Be careful with polyvitamins and other additives containing vitamin A: Pay attention to the content of vitamin A in polyvitamines and other additives that you accept.
   • Follow caution when using a large number of products rich in vitamin A: Do not use too much liver and other products rich in vitamin A, especially if you simultaneously take vitamin A.
   • Pregnant women should be particularly cautioned: Pregnant women should discuss with the doctor the intake of vitamin A in order to avoid overdose and risk of congenital defects in newborns.
   • Keep vitamin A additives in an inaccessible place for children: Children are more susceptible to the toxicity of vitamin A, therefore it is important to store vitamin A supplements in inaccessible place for them.

Chapter 6: Interaction of vitamin A C of other nutrients and drugs

6. 1 Interaction of vitamin A C of other nutrients:

   • Vitamin E: Vitamin E is an antioxidant that can protect vitamin A from oxidation and improve its assimilation.
   • Zinc: Zinc is necessary for the synthesis of RBP, a protein that transports vitamin A in the blood. Zinc deficiency can worsen the absorption and transportation of vitamin A.
   • Iron: Vitamin A can improve the absorption of iron. Vitamin A deficiency can worsen the absorption of iron and lead to iron deficiency anemia.
   • Protein: Protein is necessary for RBP synthesis. Protein deficiency can worsen the transportation of vitamin A.
   • Fat: Vitamin A is fat -soluble, therefore, for its optimal assimilation, it is necessary to consume it along with products containing fat.

7. 2 Interaction of vitamin A with drugs:

   • Retinoids: Retinoids are a group of drugs derivatives of vitamin A, which are used to treat acne, psoriasis and other skin diseases. With the simultaneous use of retinoids and additives of vitamin A, the risk of vitamin A toxicity increases.
   • Anticoagulants: Vitamin A can enhance the effect of anticoagulants such as warfarin, which can increase the risk of bleeding.
   • Antibiotics: Some antibiotics, such as tetracycline, can interact with vitamin A and increase the risk of intracranial pressure.
   • Cholestyramine and Colestyul: These drugs, used to reduce cholesterol, can bind vitamin A in the gastrointestinal tract and reduce its absorption.
   • Orlistat: Orlistat is a drug used to treat obesity, which can block fat absorption, including fat -soluble vitamins, such as vitamin A.

8. 3 Recommendations for accounting for vitamin A C Other Substances:

   • Consult a doctor or pharmacist: Before taking vitamin A additives or with the simultaneous administration of drugs, consult a doctor or pharmacist to find out about possible interactions.
   • Tell the doctor about all the drugs taken and additives: Tell the doctor about all drugs and additives that you accept so that he can evaluate the risk of interactions.
   • Caution with the simultaneous intake of vitamin A and retinoids: Do not take vitamin additives and simultaneously with retinoids without consulting a doctor.
   • Take vitamin A supplements separately from chilling, collaces and eagleistata: If you take these drugs, take vitamin adds a few hours before or after taking these drugs.
   • Control the state of health: With the simultaneous use of vitamin A and drugs, regularly visit the doctor to control the state of health and identify possible side effects.

Chapter 7: Vitamin A and special groups of children

7. 1 Premature children:

Premature children have lower reserves of vitamin A, than full -term children, and are more susceptible to vitamin A. This is due to the fact that vitamin A is mainly accumulated in the body during the last weeks of pregnancy. Premature children also have a less developed digestive system, which can impede the absorption of vitamin A. Vitamin A deficiency A in premature babies can increase the risk of chronic lung diseases, such as bronchopulmonary dysplasia, and other complications.

*   **Рекомендации для недоношенных детей:**

    *   Доношенные дети, находящиеся на грудном вскармливании, должны получать достаточно витамина А из грудного молока.
    *   Если ребенок находится на искусственном вскармливании, выбирайте смесь, обогащенную витамином А.
    *   В некоторых случаях может потребоваться дополнительное введение витамина А, особенно если у ребенка есть признаки дефицита витамина А.

7. 2 Children with chronic diseases:

Children with chronic diseases, such as cystic fibrosis, celiac disease, Crohn’s disease and other intestinal diseases, may have an increased risk of vitamin A deficiency A due to a violation of vitamin A. Chronic diseases can also have an increased need for vitamin A due to increased inflammation and immune activation.

*   **Рекомендации для детей с хроническими заболеваниями:**

    *   Регулярно проверяйте уровень витамина А в крови.
    *   Включите в рацион продукты, богатые витамином А.
    *   В некоторых случаях может потребоваться дополнительное введение витамина А.

7. 3 Children on a vegetarian or vegan diet:

Children who are on a vegetarian or vegan diet can receive a sufficient amount of carotenoids from plant foods, but their ability to convert carotenoids to retinol can be different. Some studies show that vegetarians and vegans can have a lower level of retinol in the blood than people who use animal products.

*   **Рекомендации для детей на вегетарианской или веганской диете:**

    *   Включите в рацион разнообразные продукты, богатые каротиноидами, такие как морковь, тыква, сладкий картофель, шпинат и брокколи.
    *   Готовьте продукты, богатые каротиноидами, с добавлением жира, чтобы улучшить их усвоение.
    *   В некоторых случаях может потребоваться дополнительное введение витамина А, особенно если у ребенка есть признаки дефицита витамина А.

7. 4 Children with insufficient nutrition:

Children with insufficient nutrition, especially in developing countries, are at high risk of vitamin A. deficiency of vitamin A in children with insufficient nutrition can increase the risk of infections, blindness and death.

*   **Рекомендации для детей с недостаточным питанием:**

    *   Обеспечьте достаточное питание, включающее продукты, богатые витамином А.
    *   Рассмотрите возможность добавления витамина А, особенно если у ребенка есть признаки дефицита витамина А.
    *   Проводите программы обогащения продуктов питания витамином А в районах с высоким риском дефицита витамина А.

Chapter 8: Modern studies about vitamin A and children’s health

8. 1 Vitamin A and Prevention Cancer:

Some studies show that vitamin A and carotenoids can play a role in cancer prevention. However, the results of these studies are contradictory, and additional studies are needed to confirm this connection.

8. 2 Vitamin A and bone health:

Vitamin A is necessary for the normal growth and development of bones. However, both the deficiency and an overdose of vitamin A can negatively affect bone health. Additional studies are needed to determine the optimal level of vitamin A for bone health.

8. 3 Vitamin A and brain development:

Vitamin A plays an important role in the development of the brain. Animal studies have shown that vitamin A deficiency can negatively affect cognitive functions and training. Additional studies are needed to study the effects of vitamin A on the development of the brain in people.

8. 4 Vitamin A and autoimmune diseases:

Some studies show that vitamin A can play a role in the modulation of the immune system and influence the development of autoimmune diseases. However, the results of these studies are contradictory, and additional studies are needed to confirm this connection.

8. 5 Vitamin A and metabolic syndrome:

Some studies show that vitamin A can play a role in the regulation of metabolism and influence the development of metabolic syndrome. However, the results of these studies are contradictory, and additional studies are needed to confirm this connection.

Chapter 9: Myths and errors about vitamin A and children’s health

9. 1 Myth: The more vitamin A, the better for health.

True: vitamin A is necessary for health, but an overdose of vitamin A can be toxic. It is important to observe the recommended dose of vitamin A and avoid taking high doses of vitamin A without consulting a doctor.

9. 2 Myth: Carotinoids are as effective as retinol.

True: carotenoids are provitamins A, which the body can transform into retinol. However, the effectiveness of converting carotenoids into retinol can vary depending on genetic factors, diet and health status. Retinol contained in animal products is a more effective source of vitamin A than carotenoids.

9. 3 Myth: Vitamin A deficiency is found only in developing countries.

True: Vitamin A deficiency can also be found in developed countries, especially in children with