Lecture 3 : Micronutrients

1: Vitamin A

2: Vitamin B1

3: Vitamin B2

4: Vitamin B3

5: Vitamin B5

Vitamin A:

Definition: Vitamin A is a fat-soluble vitamin essential for vision, immune function, skin health, and cell differentiation. It exists in two main forms: retinol (preformed vitamin A) found in animal-derived foods and provitamin A carotenoids (such as beta-carotene) found in plant-based foods.

Basic: Vitamin A plays a crucial role in maintaining healthy vision, particularly in low-light conditions, by supporting the function of rhodopsin, a pigment in the retina. It also contributes to the integrity of the skin and mucous membranes, aiding in wound healing and immune defense against infections.

Intermediate: In addition to its role in vision and immune function, vitamin A is involved in regulating gene expression, cell growth, and differentiation, making it essential for embryonic development, reproduction, and overall cellular health. Deficiency in vitamin A can lead to night blindness, dry skin, impaired immunity, and increased susceptibility to infections.

Advanced: Optimal vitamin A status can be achieved through a balanced diet containing a variety of vitamin A-rich foods, including liver, fish liver oil, eggs, dairy products, and orange and yellow fruits and vegetables (e.g., carrots, sweet potatoes, and mangoes). Excessive intake of preformed vitamin A from supplements or high-dose retinoid medications can lead to toxicity, characterized by symptoms such as nausea, headache, dizziness, and in severe cases, liver damage and birth defects. Provitamin A carotenoids from plant sources are considered safe and can be converted to vitamin A as needed by the body, providing a safer alternative for meeting vitamin A requirements, particularly in populations at risk of deficiency.

Vitamin B1 (Thiamine):

Definition: Vitamin B1, also known as thiamine, is a water-soluble vitamin that plays a critical role in energy metabolism, nerve function, and carbohydrate metabolism. It is involved in converting carbohydrates into energy and supporting the function of nerves and muscles.

Basic: Thiamine serves as a cofactor for several enzymes involved in the breakdown of glucose to produce ATP, the body's primary energy currency. It is particularly important for cells with high energy demands, such as those in the brain, heart, and nervous system.

Intermediate: Thiamine deficiency can result in beriberi, a condition characterized by fatigue, weakness, nerve damage, and cardiovascular dysfunction. Chronic alcohol consumption is a common cause of thiamine deficiency, as alcohol interferes with thiamine absorption and utilization.

Advanced: Dietary sources of thiamine include whole grains, fortified cereals, pork, lean meats, legumes, nuts, and seeds. Cooking methods such as boiling can leach thiamine from foods, so it's important to consume a varied diet rich in thiamine-containing foods to prevent deficiency. Thiamine supplementation may be necessary for individuals with malabsorption disorders, chronic alcoholism, or conditions that increase thiamine requirements, such as pregnancy or lactation.

Vitamin B2 (Riboflavin):

Definition: Vitamin B2, also known as riboflavin, is a water-soluble vitamin involved in energy metabolism, antioxidant defense, and the metabolism of

fats, proteins, and carbohydrates. It serves as a precursor for the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which play essential roles in numerous enzymatic reactions.

Basic: Riboflavin participates in the electron transport chain, facilitating the conversion of nutrients into usable energy (ATP) within mitochondria. It also functions as an antioxidant, helping to neutralize free radicals and protect cells from oxidative damage.

Intermediate: Riboflavin deficiency can lead to symptoms such as cracked lips, inflamed tongue, mouth ulcers, skin rashes, and sensitivity to light (photophobia). Deficiency is rare in developed countries but may occur in individuals with poor dietary intake, malabsorption disorders, or certain genetic conditions.

Advanced: Dietary sources of riboflavin include dairy products, lean meats, poultry, fish, eggs, green leafy vegetables, nuts, and fortified cereals. Riboflavin is relatively stable during cooking and food processing but can be degraded by exposure to light. Supplementation may be warranted for individuals at risk of deficiency, such as those with restricted diets, malabsorption disorders, or increased metabolic demands due to illness or intense physical activity.

Vitamin B3 (Niacin):

Definition: Vitamin B3, also known as niacin, encompasses two forms: nicotinic acid and nicotinamide, both of which serve as precursors for the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). These coenzymes play crucial roles in energy metabolism, DNA repair, and cell signaling.

Basic: Niacin is involved in the oxidation-reduction reactions of cellular respiration, facilitating the production of ATP from carbohydrates, fats, and proteins. It also supports DNA repair mechanisms and acts as a cofactor for enzymes involved in cellular metabolism and antioxidant defense.

Intermediate: Niacin deficiency can lead to pellagra, a condition characterized by the "4 Ds": dermatitis (skin rash), diarrhea, dementia, and death if left untreated. Pellagra was historically prevalent in populations consuming niacin-deficient diets heavy in maize (corn) but is now rare in developed countries due to improved dietary diversity and fortification practices.

Advanced: Dietary sources of niacin include meat, poultry, fish, peanuts, legumes, whole grains, and fortified cereals. Tryptophan, an essential amino acid found in protein-rich foods, can also be converted into niacin in the body. High-dose niacin supplementation is sometimes used therapeutically to lower cholesterol levels and triglycerides but can cause adverse effects such as flushing, itching, and liver toxicity, particularly with sustained-release formulations. Monitoring niacin intake from both dietary sources and supplements is essential to prevent toxicity and ensure optimal health.

Vitamin B5 (Pantothenic Acid):

Definition: Vitamin B5, also known as pantothenic acid, is a water-soluble vitamin essential for energy metabolism, synthesizing fatty acids, cholesterol, and steroid hormones, and supporting cellular growth and repair.

Basic: Pantothenic acid is a component of coenzyme A (CoA), which plays a central role in the synthesis and breakdown of fatty acids, amino acids, and carbohydrates. CoA is involved in numerous metabolic pathways, including the Krebs cycle (citric acid cycle) and the synthesis of acetylcholine, a neurotransmitter.

Intermediate: Pantothenic acid deficiency is rare and typically only occurs in severe malnutrition or certain metabolic disorders. Symptoms of deficiency may include fatigue, irritability, numbness, and gastrointestinal disturbances, although these are nonspecific and may overlap with other nutrient deficiencies.

Advanced: Dietary sources of pantothenic acid include meat, poultry, fish, eggs, dairy products, whole grains, legumes, and vegetables. Pantothenic acid is relatively stable during cooking and food processing, but prolonged storage and heat exposure can lead to some loss. While supplementation is generally unnecessary for individuals with a balanced diet, it may be warranted for certain populations at risk of deficiency, such as individuals with malabsorption disorders, chronic alcoholism, or increased metabolic demands due to illness or stress.