What are vitamins?

Various vitamin compounds in colourful circles

A comprehensive guide to vitamins: their types, functions, deficiency symptoms, recommended dietary allowances and sources.

Vitamins and minerals make up an integral part of our daily diet and vitamin deficiencies are often spoken about. As humans have moved away from natural and diverse foods and toward more processed foods, we have become more prone to vitamin deficiencies.

But what are these various vitamins? How do they work in our bodies? This article explains the different types of vitamins, how our bodies obtain them, their deficiency symptoms, and how do avoid vitamin deficiencies and vitamin supplements.

What are vitamins essentially?

In the early nineteenth century, nutritionists started to identify some dietary elements whose deficiency could harm the body. It was found that these were required in minimal quantities for the body to function. Although vitamin deficiency diseases have been known since the 1600s (rickets in England), it was not until 1912 that Casimir Funk, a Polish Biochemist, coined the term 'Vitamin' for these factors.

Funk derived this term by combining two words, 'vital' and 'amines.' This name reflected the common belief of those days that these factors are the essential amino acids that help to regulate various body functions. However, later discoveries have proved that this is not the case.

The research on vitamins continued into the next century, and many physiologists, chemists, biochemists and epidemiologists, contributed to this research. Over time, they were able to identify various types of vitamins and classify diseases caused by their deficiencies, for example, scurvy, rickets and xerophthalmia.

What are the different types of vitamins?

Vitamins are organic substances, i.e., they are molecules of life and have carbon as a significant element which makes up their composition. Therefore, they could be categorised on various bases, e.g., chemical nature, solubility, source, etc... However, the most commonly used classification system of vitamins is based on their solubility.

For example, vitamins could be grouped into two categories based on solubility: fat-soluble vitamins or water-soluble vitamins. Their solubility reflects their biochemical properties and biological functions.

Fat-soluble vitamins

Their name shows that these vitamins are soluble in fats and have little to no solubility in water. Hence, you should be worried about hypervitaminosis (i.e., excessive accumulation of vitamins) as much as their deficiencies. In addition, because fat-soluble vitamins are insoluble in water, the body finds it difficult to remove them through urine. Therefore, dietary supplements containing fat-soluble vitamins should only be used under the guidance of an expert dietician.

The vitamins in this category are Vitamin A, D, E, and K. These vitamins regulate various body functions, e.g., blood coagulation, immune function development, vision and bone health.

Water-soluble vitamins

As their name depicts, these vitamins are soluble in water. So, their excess is not problematic as our bodies remove them through the kidneys. However, you have to worry about their deficiency symptoms. The essential vitamins in this category are vitamin B (a complex of eight vitamins) and vitamin C.

The eight members of the B complex family are:

  • Vitamin B1 (Thiamine)

  • Vitamin B2 (Riboflavin)

  • Vitamin B3 (Nicotinamide)

  • Vitamin B5 (pantothenic acid)

  • Vitamin B6 (Pyridoxine)

  • Vitamin B7 (Biotin)

  • Vitamin B9 (folic acid/ folate)

  • Vitamin B12 (Cobalamin)

These vitamins are required for various functions, e.g., healthy skin, the health of the heart and nerves, proper development and growth, and formation of red blood cells.

What are the symptoms of vitamin deficiencies?

Despite their requirements in minimal quantities, they are still essential nutrients, and their deficiencies can't go unnoticed. Avitaminosis is the general term used for the deficiency of vitamins. Besides the general symptoms of vitamin deficiencies, the deficiency of some vitamins has been associated with diseases.

However, the common symptoms of vitamin deficiencies are:

  • Brittleness of nails and hairs

  • Tingling in feet and hands

  • Fatigue, generalised weakness, muscle cramps and pain

  • Ulcers and cracks in the mouth

  • Baldness

  • White or red bumps on the skin

  • Restless leg syndrome

  • Dermatitis, itchy scalp and excessive dandruff

  • White patches in the eyes and poor vision at night

  • Bleeding from the gums

  • Weak bones and increased incidences of bone fractures

These symptoms are not related to any specific vitamin. However, the presence of these symptoms could warn you of vitamin deficiencies.

Along with the general symptoms of avitaminosis, the deficiency of some vitamins can cause specific problems as described above.

How do our bodies get the desired vitamins?

Vitamins have different functions in the body. An exciting thing about vitamins is that our bodies can't synthesize most of them (except vitamin D and B3). So, you have to rely on food sources to avoid vitamin deficiencies. Ever since the discovery of vitamins, decades of research have highlighted various sources and requirements of different vitamins. The details about the functions of other vitamins, their dietary sources, and recommended dietary allowances are summarised individually.

Vitamin A

Also known as retinol, this vitamin is essential for the proper functioning of your immune system, night vision, and healthy inner lining of organs, e.g., nose, mouth, etc...


Critical dietary sources are seafood, liver, dairy products, leafy green vegetables, pumpkin, ripe fruits, oranges, carrots, etc...

Daily recommended allowance

The NHS recommends a daily dose of 700 mcg for men and 600 mcg for women.


The deficiency of vitamin A can cause xerophthalmia (a condition associated with inflammation and dryness of cornea and conjunctiva of eyes), night blindness, problems with bone formation, improper growth, decreased reproductive efficiency, impaired health of epithelium and reduced immunity.

Vitamin A supplements can be found here.

Vitamin D

Vitamin D occurs in two forms: ergocalciferol (D2) and cholecalciferol (D3). Your body breaks down both D2 and D3 into the active form, the calcitriol. It is required for the health of your body's muscles, bones and teeth.


Critical dietary sources are liver, eggs, sardines, other oily fishes, mushrooms and eggs.

Daily recommended allowance

A daily dose of 1o mcg is recommended by NHS, the UK, for adults and babies above one year of age.


The deficiency of Vitamin D can disturb the health of your bones by causing osteomalacia, rickets and disturbance of immune functions.

To find out more about Vitamin D supplements, click here.

Vitamin E

Also known as tocopherol, this vitamin is required for healthy skin, eyes, and normal functioning of the immune system.

Dietary sources

Recommended dietary sources are fruits and vegetables, seeds, nuts, plant oils, and cereals.

Daily recommended allowance

The NHS recommends a daily dose of 4mg for men and 3mg for women.


The deficiency of vitamin E is quite rare. However, in children, its deficiency is associated with haemolytic anaemia.

Vitamin K

This vitamin is involved in blood clotting and wound healing. It is also essential for your bone health.

Dietary sources

It is rich in green leafy vegetables, liver, egg yolk, cereal grains, dairy products and meat.

Daily recommended allowance

It varies with your body weight. You need 1mcg of vitamin K for every kg of your weight. So that would mean that person weighing 50kgs would need 50mcg of vitamin K per day.


Disturbed blood clotting leads to bleeding problems, e.g., bleeding gums.

Vitamin C

This vitamin is also known as ascorbic acid. It is required for the health and integrity of your cells, healthy cartilage and bones, and healthy skin and blood vessels. This vitamin is perhaps the single most important vitamin for your health, alongside water and healthy sleep.

Dietary sources

It is present in citrus fruits (oranges, lemons, strawberries, etc...) and vegetables, e.g., potatoes, broccoli, brussels sprouts and peppers.

Daily recommended allowance

It would be best to have 40mg or more of vitamin C daily.


The deficiency of Vitamin C causes scurvy. This disease is associated with bleeding gums, slow and improper wound healing, teeth loss, weakness and death in extreme cases.

Vitamin B1

Also known as thiamine, this vitamin is critical for the health of your digestive system and nervous system.

Dietary sources

It is naturally present in vegetables, fruits (e.g., oranges and bananas), eggs, potatoes, brown rice, whole grains, liver and pork.

Daily recommended allowance

The NHS recommends a daily dose of 1mg for men and 0.8mcg for women.

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Its deficiency causes an acute disease called Beriberi. The condition has two forms, dry and wet. The symptoms of dry Beriberi are nerve problems (tingling or burning sensations), weakness of limbs, and problems with the coordination of body movements. At the same time, wet Beriberi causes oedema and heart failure. Thiamine deficiency is also associated with Wernicke's encephalopathy, which causes nerve problems.

Vitamin B2

Also known as riboflavin, this vitamin is required for your skin, eyes, nervous system and digestive health.

Dietary sources

It is obtained from dairy products, asparagus, green beans and fruits.

Daily recommended allowance

A daily dose of 1.1-1.3mg is recommended. The upper value is for men, while the lower is for women.


Its deficiency causes sore throat, swollen and painful tongue and mouth and dermatitis.

Vitamin B3

This vitamin is also known as Niacin which is essential for your digestive system, skin, and nerve health. It occurs naturally in 2 forms: nicotinamide and nicotinic acid.

Dietary sources

It is found abundantly in different vegetables, nuts, mushrooms, fish, eggs, wheat flour, etc...

Daily recommended allowance

The NHS recommends a daily dose of 13.2mg for women and 16.5mg for men.


Its deficiency causes pellagra, a condition characterised by diarrhoea, dermatitis, dementia (loss of memory) and death.

Vitamin B5

It is commonly known as pantothenic acid. It is essential for digestion and metabolism.

Dietary sources

Avocados, meats, broccoli, kidney, liver, chicken, and beef are rich sources of pantothenic acid.

Daily recommended allowance

Although no daily allowance is recommended in the UK, some sources mention a figure of 5mg per day.


The abnormal sensation of the skin can occur without any physical cause

Vitamin B6

Also known as pyridoxine, it helps in the metabolism of proteins and carbohydrates. It is also involved in forming red blood cells and haemoglobin, the principal oxygen-carrying compound.

Dietary sources

Fruits (e.g., bananas), milk, vegetables, nuts, meats (chicken, pork, turkey, seafood), etc..., are naturally rich in pyridoxine.

Daily recommended allowance

The daily allowance recommended is 1.4mg for men and 1.2mg daily for women.


It can cause disease of the peripheral nerves (causing paralysis) and anaemia.

Vitamin B7

Also known as Biotin, this vitamin is required to synthesize essential fatty acids and is also involved in the metabolism of proteins and carbohydrates. It is present in various beauty and cosmetic products because it strengthens the skin, nails, and hair.

Dietary sources

Meats, nuts, seeds, sweet potatoes, green leafy vegetables, fortified cereals, egg yolk (raw), peanuts, liver, etc..., are natural sources of Biotin.

Daily recommended allowance

A daily requirement of 30 mcg is enough for both genders.


Its deficiency can cause dermatitis and enteritis.

Vitamin B9 (Folate/Folic acid)

Folate is the natural form of folic acid. It is required to form red blood cells as its deficiency can cause folate deficiency anaemia. It also reduces the risk of congenital disabilities of the brain and nervous system, e.g., spina bifida.

Dietary sources

Cereals, pasta, green vegetables, legumes (chickpeas, kidney beans, etc...), bread, animal liver, and folate-fortified breakfast cereals are rich sources of dietary folate.

Daily recommended allowance

A 400 mcg daily dose is required during early pregnancy.


Folate deficiency can cause anaemia. In addition, if the deficiency occurs in early pregnancy, the baby can develop neural tube defects.

Vitamin 12 (cobalamin)

This vitamin is required for nerve health, proper digestion and the formation of red blood cells. Its deficiency can cause B12 deficiency anaemia. It is also necessary for the appropriate use of folate by the body.

Dietary sources

Poultry meat, eggs, milk, seafood, cheese and fortified breakfast cereals are good sources of B12.

Daily recommended allowance

The NHS recommended daily dose of b12 is 1.5mg.


The typical problems are loss of memory and lack of coordination (of body movements), particularly in infants.

How can you avoid vitamin deficiencies?

After taking a deep dive through the vitamins, you should have understood the importance of vitamins for your health.

The general recommendations to avoid vitamin deficiencies are to:

  • Diversify your diet by adding as many fruits and vegetables as possible as sources of vitamins and minerals.

  • You can fortify your summer drinks with a variety of water-soluble vitamins.

  • Fortified foods should be considered if you notice any vitamin deficiency.

  • Focus on your gut health. If your gut is not working correctly, you will not be able to take maximum advantage of even a balanced diet, and most vitamins and minerals will be flushed out into your faeces.

  • Replace saturated fats in your diet with vegetable oils to maintain a healthy weight.


Vitamins and minerals are essential for your health. Your balanced diet should incorporate all the vitamins to ensure good health. However, most vitamins are available in dietary supplements which also do the job of keeping you healthy and make you ready to seize the day.

For a full range of blood tests and supplements, visit our Welzo Online Pharmacy Page.

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