7. Vitamins: A Complete Guide to Classification, Functions, and Deficiency Diseases

VITAMINS: A TEACHER’S COMPREHENSIVE GUIDE

Welcome, future pharmacists and healthcare professionals!

As a pharmacy educator with years of experience teaching biochemistry, I have always emphasized that vitamins are essential micronutrients that keep the body functioning properly. Although they are required in tiny amounts, their absence can lead to devastating deficiency diseases. Vitamins do not provide energy directly, but they help the body use proteins, carbohydrates, and fats effectively. Understanding vitamins is essential for pharmacy students to grasp nutritional health, disease prevention, and the role of supplements in therapy.

In this comprehensive guide, I will take you through the fascinating world of vitamins. We will explore their definition, classification, sources, functions, coenzyme forms, recommended dietary allowances, and deficiency diseases. By the end of this article, you will have a solid understanding of why vitamins are essential for life and how they are relevant to pharmacy practice. Let us begin.

WHAT ARE VITAMINS?

Vitamins are organic compounds required in small quantities for normal body functions such as energy production, immunity, vision, blood formation, and tissue repair. They do not provide energy but help the body use proteins, carbohydrates, and fats effectively.

Vitamins cannot be produced in sufficient amounts by the body and must be obtained from food. They are essential micronutrients required by the body in small amounts for growth, metabolism, immunity, and maintaining good health.

CLASSIFICATION OF VITAMINS

Vitamins are classified into two main groups based on their solubility:

1. Fat-Soluble Vitamins

These vitamins dissolve in fats and are stored in the liver and fatty tissues. They are absorbed along with dietary fats and can accumulate in the body, leading to toxicity if consumed in excess.

• Vitamin A (Retinol)
• Vitamin D (Cholecalciferol)
• Vitamin E (Tocopherol)
• Vitamin K (Phylloquinone)

2. Water-Soluble Vitamins

These vitamins dissolve in water and are not stored in the body. Excess is excreted in urine, so they need to be consumed regularly. They are generally non-toxic even in high doses, as excess is eliminated.

• Vitamin B Complex (B1, B2, B3, B5, B6, B7, B9, B12)
• Vitamin C (Ascorbic acid)

FAT-SOLUBLE VITAMINS

Vitamin A (Retinol)

Sources: Carrots, spinach, eggs, liver, milk, and other dairy products. Beta-carotene from plant sources is converted to vitamin A in the body.

Chemical Nature: Unsaturated alcohol with a beta-ionone ring.

Functions: Essential for vision (especially night vision), skin health, immunity, and growth. It plays a crucial role in the maintenance of epithelial tissues.

Coenzyme Form: Retinal (in the vision cycle).

RDA: 600–900 μg/day (varies by age and sex).

Deficiency: Night blindness, dry skin, xerophthalmia (dryness of the conjunctiva and cornea), and increased susceptibility to infections.

Vitamin D (Cholecalciferol)

Sources: Sunlight (UV rays trigger synthesis in the skin), fish oil, milk, egg yolk, and fortified foods.

Chemical Nature: A steroid derivative.

Functions: Regulates calcium and phosphorus absorption, promoting bone health and mineralization. It is essential for normal growth and development of bones.

Coenzyme Form: Calcitriol (the active form of vitamin D).

RDA: 400–800 IU/day (higher doses may be recommended for deficiency).

Deficiency: Rickets in children (softening of bones), osteomalacia in adults (bone pain and muscle weakness), and increased risk of osteoporosis.

Vitamin E (Tocopherol)

Sources: Vegetable oils, nuts, seeds, green leafy vegetables, and whole grains.

Chemical Nature: Tocopherols and tocotrienols.

Functions: A powerful antioxidant that protects cell membranes from oxidative damage. It helps maintain healthy skin and eyes and supports the immune system.

Coenzyme Form: None (acts directly as an antioxidant).

RDA: 8–15 mg/day.

Deficiency: Muscle weakness, hemolytic anemia (destruction of red blood cells), and neurological problems.

Vitamin K (Phylloquinone)

Sources: Green leafy vegetables (spinach, kale, cabbage), liver, and fermented foods.

Chemical Nature: A quinone derivative.

Functions: Essential for blood clotting (synthesis of clotting factors in the liver). It also plays a role in bone metabolism.

Coenzyme Form: Vitamin K hydroquinone.

RDA: 75–120 μg/day.

Deficiency: Bleeding disorders, delayed blood clotting, and easy bruising.

WATER-SOLUBLE VITAMINS

Vitamin B1 (Thiamine)

Sources: Whole grains, nuts, pork, cereals, and legumes.

Functions: Essential for energy metabolism, particularly in carbohydrate metabolism. It is also important for nerve function.

Coenzyme Form: TPP (Thiamine pyrophosphate).

Deficiency: Beri-beri (nerve damage, muscle weakness, and cardiovascular problems), Wernicke’s syndrome (neurological disorder).

Vitamin B2 (Riboflavin)

Sources: Milk, eggs, green leafy vegetables, and fortified cereals.

Functions: Helps in oxidation-reduction reactions, energy production, and cellular respiration.

Coenzyme Form: FMN (Flavin mononucleotide) and FAD (Flavin adenine dinucleotide).

Deficiency: Cracks at the corners of the mouth (angular stomatitis), dermatitis, and sore throat.

Vitamin B3 (Niacin)

Sources: Meat, fish, poultry, whole grains, and peanuts.

Functions: Essential for energy production, DNA repair, and cellular signalling.

Coenzyme Form: NAD (Nicotinamide adenine dinucleotide) and NADP (Nicotinamide adenine dinucleotide phosphate).

Deficiency: Pellagra, characterized by the “4 Ds”: Dermatitis, Diarrhea, Dementia, and Death.

Vitamin B5 (Pantothenic Acid)

Sources: Meat, eggs, whole grains, and legumes.

Functions: A component of Coenzyme A, which is essential for fatty acid metabolism and energy production.

Deficiency: Fatigue, burning feet syndrome, and gastrointestinal disturbances.

Vitamin B6 (Pyridoxine)

Sources: Fish, bananas, nuts, poultry, and fortified cereals.

Functions: Amino acid metabolism, neurotransmitter synthesis, and red blood cell formation.

Coenzyme Form: PLP (Pyridoxal phosphate).

Deficiency: Anemia, nerve damage, and dermatitis.

Vitamin B7 (Biotin)

Sources: Egg yolk, nuts, soybeans, and whole grains.

Functions: Acts as a coenzyme for carboxylation reactions in metabolism.

Deficiency: Hair loss, dermatitis, and neurological symptoms.

Vitamin B9 (Folic Acid)

Sources: Green leafy vegetables, liver, legumes, and fortified grains.

Functions: DNA synthesis, red blood cell formation, and prevention of neural tube defects in foetuses.

Coenzyme Form: THF (Tetrahydrofolate).

Deficiency: Megaloblastic anemia, birth defects (neural tube defects), and increased risk of heart disease.

Vitamin B12 (Cobalamin)

Sources: Meat, fish, poultry, eggs, milk, and dairy products (not found in plant foods).

Functions: Nerve function, red blood cell formation, and DNA synthesis.

Coenzyme Form: Methylcobalamin and Adenosylcobalamin.

Deficiency: Pernicious anemia (due to lack of intrinsic factor), nerve damage, and cognitive impairment.

Vitamin C (Ascorbic Acid)

Sources: Citrus fruits (oranges, lemons), amla (Indian gooseberry), tomatoes, and green leafy vegetables.

Functions: Collagen synthesis (essential for skin, blood vessels, and bones), wound healing, antioxidant activity, and immune support.

Coenzyme Form: None (acts directly).

RDA: 65–90 mg/day (higher doses may be needed during illness).

Deficiency: Scurvy, characterized by bleeding gums, poor wound healing, and joint pain.

SUMMARY: VITAMINS AT A GLANCE

Vitamin	Sources	Primary Function	Deficiency Disease
Vitamin A	Carrots, liver, milk	Vision, immunity, skin	Night blindness
Vitamin D	Sunlight, fish oil	Calcium absorption, bone	Rickets, osteomalacia
Vitamin E	Nuts, vegetable oils	Antioxidant	Muscle weakness, anemia
Vitamin K	Green vegetables	Blood clotting	Bleeding disorders
Vitamin B1	Whole grains, pork	Energy metabolism	Beri-beri
Vitamin B2	Milk, eggs	Oxidation-reduction	Dermatitis, stomatitis
Vitamin B3	Meat, grains	Energy production	Pellagra
Vitamin B5	Meat, eggs	Coenzyme A function	Fatigue, burning feet
Vitamin B6	Fish, bananas	Amino acid metabolism	Anemia, nerve damage
Vitamin B7	Nuts, egg yolk	Carboxylation	Hair loss, dermatitis
Vitamin B9	Leafy vegetables	DNA synthesis	Megaloblastic anemia
Vitamin B12	Meat, milk	Nerve function, RBC	Pernicious anemia
Vitamin C	Citrus fruits	Collagen synthesis	Scurvy

CLINICAL SIGNIFICANCE OF VITAMINS

Vitamins have significant clinical importance. Deficiency diseases can be prevented or treated with appropriate supplementation. However, excessive intake of vitamins—especially fat-soluble vitamins—can be toxic. For example, hypervitaminosis A can cause liver damage, and hypervitaminosis D can cause hypercalcemia. Therefore, understanding the recommended dietary allowances is essential for safe and effective supplementation.

A TEACHER’S PRACTICAL INSIGHTS

Over my years of teaching, I have developed a few key insights about vitamins that I always share with my students:

• Think about the patient: Vitamin deficiencies are common in certain populations, including the elderly, pregnant women, and people with malabsorption disorders. Understanding vitamin function is essential for patient care.
• Know your vitamins: Understanding the difference between fat-soluble and water-soluble vitamins is essential for understanding storage, toxicity, and dosing.
• Remember the deficiency diseases: The classical deficiency diseases are important clinical signs that can guide diagnosis and treatment.

FREQUENTLY ASKED QUESTIONS (FAQs)

1. What are vitamins?

Vitamins are organic compounds required in small quantities for normal body functions. They do not provide energy but help the body use proteins, carbohydrates, and fats effectively.

2. What is the difference between fat-soluble and water-soluble vitamins?

Fat-soluble vitamins (A, D, E, K) dissolve in fats and are stored in the body. Water-soluble vitamins (B-complex and C) dissolve in water and are not stored; excess is excreted in urine.

3. What is the RDA?

RDA stands for Recommended Dietary Allowance—the daily intake level of a nutrient considered sufficient to meet the requirements of most healthy individuals.

4. What is the deficiency disease for vitamin C?

Vitamin C deficiency causes scurvy, characterized by bleeding gums, poor wound healing, and joint pain.

5. What is the function of vitamin D?

Vitamin D regulates calcium and phosphorus absorption, promoting bone health and mineralization.

6. Why are vitamins important for pharmacy students?

Vitamins are essential for understanding nutritional health, disease prevention, and the role of supplements in therapy. Many drugs interact with vitamins, and understanding these interactions is important for safe prescribing.

7. Can vitamins be toxic?

Yes, especially fat-soluble vitamins (A, D, E, K), which are stored in the body. Excessive intake can lead to toxicity. Water-soluble vitamins are generally non-toxic because excess is excreted.

SUMMARY

Vitamins are essential organic micronutrients required in small amounts for growth, metabolism, immunity, and overall health. They are divided into fat-soluble vitamins (A, D, E, K) that are stored in the liver and fat tissues, and water-soluble vitamins (B-complex and C) that are not stored and are excreted in urine.

Each vitamin has specific food sources, biochemical functions, and often a coenzyme form that participates in metabolic reactions. Deficiency produces characteristic diseases such as night blindness, rickets, beri-beri, pellagra, scurvy, and anemias. Excessive intake—especially of fat-soluble vitamins—can be toxic.

Understanding vitamins is essential for pharmacy students to link vitamin functions and deficiencies with clinical signs, drug therapy, and dietary supplementation. As I always tell my students: “Vitamins are the spark plugs of life. Understand them, and you understand the foundation of nutritional health.”

REFERENCES & FURTHER READING

• Berg, J. M., Tymoczko, J. L., & Gatto, G. J. (2019). Biochemistry (9th ed.). W.H. Freeman and Company.
• Murray, R. K., Bender, D. A., Botham, K. M., et al. (2021). Harper’s Illustrated Biochemistry (32nd ed.). McGraw-Hill Education.
• Nelson, D. L., & Cox, M. M. (2017). Lehninger Principles of Biochemistry (7th ed.). W.H. Freeman and Company.
• National Institutes of Health (NIH). (2023). Vitamin and Mineral Supplement Fact Sheets. Retrieved from NIH Office of Dietary Supplements.
• World Health Organization (WHO). (2023). Vitamin and Mineral Deficiency Resources. Retrieved from WHO Official Website.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare professionals for medical concerns.