Vitamins: Roles, Types, Dietary Sources, Functions, Deficiency Disorders, Symptoms, Practice Problems and FAQs

We all follow a sleep-wake cycle and we know that for maintaining proper health at least 7 hours of daily sleep is necessary. But have you ever wondered why on some days you feel tired just after waking up from a good sleep? Well if you are not stressed or sick and even then feel tired, it may be because of deficiency of vitamins. Can you recall how many times your mom tried to make you eat fruits and vegetables? It is because of the fact that fruits and vegetables are a rich source of vitamins.

Fig: Balanced diet

You have also heard that a balanced diet is good for our health. Why is it so? A balanced diet contains all the essential elements that the human body needs. It includes carbohydrates, fats, proteins, vitamins, minerals and water. The carbohydrates, proteins and fats are essential because they provide energy and help in growth and development. These are macronutrients and are required in large amounts. Water is essential, because it is involved in metabolic reactions of the cell. Vitamins and minerals, on the other hand, are micronutrients. They are required in less amounts. They do not provide energy but their deficiency can cause disorders. In this article let’s take a deep dive into details of the structures, functions and disorders of vitamins.

Table of contents

Vitamins
Role of vitamins
Types of essential vitamins
Functions of essential vitamins
Vitamin deficiency disorders and common symptoms
Practice Problems
FAQs

Vitamins

Vitamins are organic compounds that perform specific biological functions essential for normal growth and functioning of the organism. These are considered as accessory food factors. Casimir Funk in 1912 coined the term ‘vitamine’. All the 13 vitamins essential for us are generally available in our diet. Fresh fruits and vegetables are a rich source of vitamins. These molecules do not provide us energy, but are required as their deficiency leads to disorders.

Fig: Essential vitamins

Roles of vitamins

Every vitamin plays a significant role in our body. The overall roles of the essential vitamins in our body are as follows:

They boost the immune system.
Some vitamins are antioxidants and delay ageing.
They prevent or delay certain types of cancers.
They keep the nervous system healthy.
They aid in calcium absorption and thereby strengthening bones and teeth.

Types of essential vitamins

Based on the solubility in water or oil, vitamins are classified into two categories as follows:

Water soluble vitamins
Fat soluble vitamins

Water soluble vitamins

These are soluble in water but not in fats and oils. They can be found in a wide range of foods, especially green vegetables and fresh fruits.

Structures and scientific names of water soluble vitamins

The following table contains the structure and scientific names of water soluble vitamins:

Names of vitamins	Structures of vitamins
Vitamin B₁or thiamine	Fig: Thiamine
Vitamin B₂or riboflavin	Fig: Riboflavin
Vitamin B₃, niacin or nicotinic acid	Fig: Niacin or nicotinic acid
Vitamin B₅or pantothenic acid	Fig: Pantothenic acid
Vitamin B₆or pyridoxine	Fig: Pyridoxine
Vitamin B₇or biotin	Fig: Biotin
Vitamin B₉, folacin or folic acid	Fig: Folacin or folic acid
Vitamin B₁₂or cyanocobalamin	Fig: Cyanocobalamin
Vitamin C or ascorbic acid	Fig: Ascorbic acid

Dietary sources of water soluble vitamins

The following table contains the dietary sources of water soluble vitamins:

Names of vitamins	Dietary sources of vitamins
Vitamin B₁	Pulses, meats, yeasts, cereals, and sprouted beans
Vitamin B₂	Yoghourts, Pulses, green vegetables, milks and yeasts
Vitamin B₃	Fishes, meats, cereals, grains, pulses, yeasts and livers
Vitamin B₅	Eggs, yeasts and most of the foods
Vitamin B₆	All plant and animal tissues
Vitamin B₇	Yeasts, livers and kidneys
Vitamin B₉	Fishes, livers and vegetables. It is also produced by bacteria in colon
Vitamin B₁₂	Milks, kidneys, meats, eggs and fishes. Bacteria in the colon of humans and in the digestive tract of cattle also produce this vitamin
Vitamin C	Green vegetables, Citrus fruits like oranges and lemons

Fat soluble vitamins

These vitamins are soluble in fats and oils. They are absorbed and stored in the same way as fats are absorbed and stored in the body's fatty tissues and liver. They are present in a wide range of plant and animal foods and dietary supplements.

Structures and scientific names of fat soluble vitamins

The following table contains the structures and scientific names of fat soluble vitamins:

Names of vitamins	Structures of vitamins
Vitamin A or retinol	Fig: Retinol
Vitamin D or calciferol	Fig: Calciferol
Vitamin E or tocopherol	Fig: Tocopherol
Vitamin K or phylloquinone	Fig: Phylloquinone

Dietary sources of fat soluble vitamins

The following table contains dietary sources of fat soluble vitamins:

Names of vitamins	Dietary sources of vitamins
Vitamin A	Cod liver oils, carrots, maizes, spinaches, butters, and milks
Vitamin D	Cod liver oils, by the action of sunlight on the skin, shark liver oils and eggs
Vitamin E	Brown flours, vegetable oils, green vegetables, germinated wheats and seeds
Vitamin K	Wheat germs, cabbages and corianders. It is also synthesised by the bacteria of the large intestine

Functions of essential vitamins

The following table contains the major functions of vitamins:

Vitamins	Functions of vitamins
Vitamin A	It is the primary component of retinal pigments. It encourages normal vision. It promotes bone and tooth growth. It helps in the maintenance of epithelial tissues.
Vitamin B₁	It functions as a respiratory coenzyme which is required for decarboxylation, particularly during the Krebs cycle.
Vitamin B₂	It helps in maintaining healthy skin and oral mucosa.
Vitamin B₃	It is required for the healthy functioning of the nervous and digestive systems. It lowers cholesterol level. It is good for skin and hair. It is required for enzyme synthesis. It forms coenzymes NAD and NADP which are required as hydrogen acceptors in cellular respiration.
Vitamin B₅	It forms coenzyme A that activates the carboxylic acid in cellular metabolism.
Vitamin B₆	It forms coenzymes such as pyridoxal phosphate and pyridoxamine phosphate and is involved in many enzyme reactions of the amino acid metabolism..
Vitamin B₇	It is required as a coenzyme for carboxylation reaction in cells.
Vitamin B₉	It promotes DNA synthesis. It also helps in maturation of RBCs.
Vitamin B₁₂	It promotes DNA synthesis. It also helps in maturation of RBCs.
Vitamin C	It is involved in the repair and maintenance of cartilage, bone and teeth. It aids in formation of tendons, ligaments and blood vessels. It helps in wound healing.
Vitamin D	It helps in the absorption of Ca2+ from the small intestine. It is also required for the maintenance and growth of the bone.
Vitamin E	It prevents unsaturated fatty acids and vitamin A oxidation.
Vitamin K	It helps in the coagulation of blood.

Vitamin deficiency disorders and common symptoms

The following table contains the major vitamin deficiency disorders and common symptoms:

Vitamins	Deficiency disorders	Common symptoms
Vitamin A	Xerophthalmia (a dry cornea with no tear secretion).	Presence of dry, wrinkled conjunctiva. Presence of ulcers or scars on cornea.
Vitamin A	Night blindness - If not treated, xerophthalmia leads this disorder	Blurry vision at night. Difficulty in seeing in dim light. Facing trouble in light to dark adaptations.
Vitamin B₁	Beriberi	Loss of sensation in hands and feet. Difficulty in walking. Loss of muscle functions and paralysis of the lower legs.
Vitamin B₂	Cheilosis (An inflammatory condition that causes cracking, crusting, and scaling of the mouth corners) and skin disorder.	Redness and rashes on skin. Presence of blistered, cracked and painful skin at the corners of mouth.
Vitamin B₃	Pellagra	Characterised by 3Ds such as dermatitis, dementia and diarrhoea. It can lead to death too.
Vitamin B₅	Metabolic perturbation and neurodegeneration	Fatigue Muscle cramps. Poor motor coordination.
Vitamin B₆	Microcytic anaemia - Presence of smaller sized red blood cells.	Fatigue Weakness Tiredness Loss of stamina. Dizziness Pale skin Skin bruises easily.
Vitamin B₇	Dermatitis and skin problems	Red rashes around eyes and nose. Lethargy Alopecia or hair loss. Nausea Ataxia or loss of body control.
Vitamin B₉	Megaloblastic anaemia (abnormally large red blood cells)	Pale skin Lack of energy Irritability Decreased appetite. Diarrhoea
Vitamin B₁₂	Pernicious anaemia/ Addison’s anaemia (type of megaloblastic anaemia, due to decreased absorption of B₁₂)	Fatigue Chest pain Weakness Pale skin Headaches Unsteady gait Depression Dementia Memory loss happens in case of prolonged deficiency.
Vitamin C	Scurvy	Swollen and bleeding gums. Dry and scaly skin. Bulging eyes. Easy bruising.
Vitamin D	Rickets in children	Delayed growth. Delayed motor skills. Bowed legs or knock knees.
Vitamin D	Osteomalacia in adults	Muscle cramps. Pain in bones and joints. Presence of easily breakable bones.
Vitamin E	Reproductive failure	Failure to conceive.
Vitamin E	Muscular dystrophy (nutritional)	Muscle weakness. Difficulty in standing. Unsteady and waddling gait. Frequent falling.
Vitamin K	Bleeding disorder	Easy bruising. Small blood clots under nails. Bleeding from the mucous membranes present inside the body. Dark black or tar-like stool with blood clots.

Practice Problems

Q1. Fatigue, weakness, loss of stamina, and small sized RBCs are common symptoms of deficiency of which vitamin?

a. Vitamin C
b. Vitamin B₆
c. Vitamin B₉
d. Vitamin B₁₂

Solution: Vitamin C deficiency causes scurvy, that is characterised by swollen and bleeding gums. Vitamin B₆ deficiency causes microcytic anaemia (small sized RBCs) and the person feels tired, weak, and fatigued. Vitamin B₉ deficiency causes megaloblastic anaemia where the size of the RBCs are abnormally large. Deficiency of vitamin B₁₂ causes pernicious anaemia. It is a type of megaloblastic anaemia. Hence, the correct option is b.

Q2. If a person is suffering from pellagra, which of the following diets will help?

a. Diet rich on eggs, carrots and spinach
b. Diet rich in yoghurts, pulses, green vegetables and milks
c. Diet rich in green vegetables and fruits like oranges and lemons
d. Diet rich in fishes, meats, grains, yeasts and livers

Solution: The symptoms given in question are related to the deficiency disorder called Pellagra. It is caused by vitamin B₃ deficiency. Food items like fishes, meats, cereal grains, livers and yeasts are a rich source of vitamin B₃. So the person suffering from pellagra can include the mentioned food items in the diet. Hence, the correct option is d.

Q3. Which of them is a water soluble vitamin?

a. Vitamin A
b. Vitamin D
c. Vitamin E
d. Vitamin B

Solution: Vitamins A, D, E and K are fat soluble vitamins. Vitamin B complex and vitamin C are all water soluble vitamins. Hence, the correct option is d.

Q4. Which of the following is also called the clotting vitamin?

a. Vitamin K
b. Vitamin A
c. Vitamin C
d. Vitamin D

Solution: Deficiency of vitamin K (phylloquinone) causes excessive bleeding from injuries. This vitamin helps in activation of certain clotting proteins for blood clotting. Therefore, it is called the clotting vitamin. Hence, the correct option is a.

FAQs

Q1: How can I fulfil my vitamin requirements if my diet is not sufficient?
Answer: As you can understand now, although vitamins are micronutrients, they are of great significance to our body. Therefore, it is important to maintain adequate levels of vitamins in our body. Sometimes, when our diet is not sufficient in providing all the vitamins, we might have to switch to their supplements. But the vitamin supplements must be taken under supervision and in recommended doses by a doctor.

Q2: What will happen if someone consumes too much vitamins?
Answer: Multivitamin overdose can cause various complications like cloudy urine, frequent urination, dry cracking lips, increased sensitivity to light, irregular heartbeats, bone and joint pains, muscle pain, weakness, fatigue, irritability, appetite loss, stomach pain, etc.

Q3: What are the differences between minerals and vitamins?
Answer: Vitamins are organic molecules that occur naturally in the food we eat. Examples include vitamin A, D, E, K, B, and C. These help in enhancing immunity and are required for normal growth and development of the body. Their deficiency leads to various disorders. Minerals are inorganic chemicals that are required for bone and muscle health, and proper functioning of the body. Some minerals may also help in proper enzyme functioning. Examples include calcium, iron, sodium, potassium, etc.

Q4: What are antioxidants?
Answer: The chemicals or compounds that prevent oxidation are called antioxidants in general terms. In physiology these are chemicals that remove potentially damaging oxidising agents in a living organism. In our body, antioxidants neutralise the free radicals that can cause harm. If left unchecked the levels of free radicals will increase and can lead to illnesses like heart attack and cancer. Our body generates its own free radicals, but they are also found in plant and animal products. Vitamin C and vitamin E are some very common and easily available antioxidants.