Sight and Life - Vitamins: a brief guide

Vitamins: a brief guide A Sight and Life publication

Vitamins: a brief guide

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What is a vitamin?

Sorghum crop in Kenya

Vitamins are organic nutrients which are essential for life. The human body requires these nutrients to ensure normal metabolism, growth and physical well-being. Most vitamins are not made in the body, or only in insufficient amounts to meet our needs. They therefore have to be obtained primarily through the food we eat.

Vitamins are classed as micronutrients, and are present in food in minute quantities compared to macronutrients (protein, carbohydrates and fat). In industrialized countries, the average adult eats approximately 600 g of food per day on a dry-weight basis, of which less than 1 g consists of vitamins.

Each of the 13 vitamins known today has specific functions in the body, which makes each of them unique and irreplaceable. No single food contains the full range of vitamins, and inadequate vitamin intake results in vitamin deficiency disorders. A balanced and varied diet is therefore vital to meet the body’s vitamin requirements.

Of the 13 known vitamins, four are fat-soluble, namely vitamins A, D, E and K. The others are water-soluble: vitamin C and the B-complex, consisting of vitamins B1, B2, B6, B12, niacin, folic acid, biotin and pantothenic acid.

Retinol β-carotene Calciferol Tocopherol Phylloquinone Thiamine Riboflavin Niacin Pantothenic acid Pyridoxine Biotin Folic acid Cobalamin Ascorbic acid

Vitamin A Provitamin A Vitamin D Vitamin E Vitamin K Vitamin B1 Vitamin B2 Vitamin B3 Vitamin B5 Vitamin B6 Vitamin B7 Vitamin B9 Vitamin B12 Vitamin C

1912

1926

1941

1931

1934

1931

1936

1920

1897

1929

1922

1918

1831

1909

Discovery

1928

1948

1941

1935

1938

1938

1936

1933

1926

1939

1936

1932

1831

1931

Isolation

1933

1956

1946

1942

1938

1940

1937

1935

1936

1939

1938

1936

1930

1931

Structure

1933

1972

1946

1943

1939

1940

1994

1935

1936

1939

1938

1959

1950

1947

Synthesis

This data has been assembled in good faith and on the basis of extensive secondary research it should be noted, however, that some sources disagree concerning individual dates.

Alternative name

Local fruits on a market in Bangladesh Vitamin

The history of vitamins

The discovery of the concept of vitamins

Various types of rice sold on a market in Bangladesh

A century ago, a Polish-American scientist attempted to isolate the first vitamin (B1) from rice bran. Casimir (born Kazimierz) Funk named his discovery “vitamine”, believing that this was an amine vital for life. This coinage has come down to us in the slightly altered form of “vitamin.” Funk’s breakthrough discovery played a decisive role in the development of an entire scientific framework of thought, which the world now takes for granted.

Funk (1884 –1967) was the first scientist to suggest the existence of an entire family of organic substances essential for life, and the first to give these substances a name that made their function clear – even though most vitamins were later shown not to be amines. He was not the only scientist working in this field at the time, but he was, one might say, the Godfather of the vitamins movement.

In a distinguished scientific career spanning two world wars, Funk studied and worked in Europe and the United States. He had roles in academia and industry, improved manufacturing methods for commercial drugs, and became President of the Funk Foundation for Medical Research. Although he never received a Nobel Prize for his work, the Polish Institute of Arts and Sciences of America presents the Casimir Funk Natural Sciences Award annually to a Polish-American scientist.

How the vitamins got their names

Locally grown legumes on a market stall in Zambia

The first vitamin to be named was vitamin A. The use of the letter A was the brainchild of the American biochemist Elmer McCollum. He rejected Casimir Funk’s term ‘vitamine’ in favor of ‘Unidentified dietary factor fat-soluble A’ because the substance discovered by McCollum did not contain nitrogen (amines are organic compounds derived from ammonia, and always contain nitrogen).

In 1921, the British biochemist Sir Jack Cecil Drummond suggested combining the use of letters of the alphabet with the term ‘vitamin’ to denote a range of related organic micronutrients. These micronutrients consequently became known as vitamins A, B, C and so on.

The eight water-soluble B vitamins were originally thought to be a single substance class, but were subsequently found to be chemically distinct from one another, which is why they are differentiated by means of suffixed numbers – B1, B2 and so forth.

Vitamins in human nutrition

While plants and micro-organisms can themselves produce the vitamins necessary for the metabolism, humans and animals lost this ability during the course of evolution. Lacking the enzymes necessary for synthesizing vitamins in the body, humans and animals therefore have to take these in via the diet (with the exception of vitamin D, which is synthesized via the action of sunlight).

It was recognized more than 3,500 years ago that foods containing vitamins are essential for health and well-being. The earliest records to have come down to us on this subject relate to the use of specific foods like liver – which contains vitamin A – to prevent diseases such as night blindness. Nevertheless the concept of vitamins per se was quite unknown until very recently.

A balanced diet is necessary for adequate vitamin intake. A lack of the necessary vitamins in the diet can lead to vitamin deficiency disorders, such as scurvy (vitamin C deficiency),and beriberi (vitamin B1 deficiency).

Since the beginning of the 20th century, our knowledge of the biological function of vitamins on the molecular and cellular level has increased significantly. This understanding is reflected by the award of 20 Nobel Prizes in this field between 1928 and 1967. Despite intensive research efforts, however, no additional vitamins have been added to the list of 13 vitamins defined during the 20th century.

Fruits, vegetables, dairy and animal products provide a well-balanced diet

A

Retinol | β-carotene

Discovery of active ingredient: 1909 | 1831 (Provitamin A) Isolation: 1931 | 1831 (Provitamin A)

Prime natural sources Animal products

Vegetable products

Liver | Egg yolk | Dairy products

Fruits | Leafy vegetables | Carrots

Animal products: Liver, egg yolk, butter, whole milk, cheese Vegetable products in the form of carotenoids (provitamin A): Certain fruits (i.e. melon, apricot), green leafy vegetables (i.e. spinach, broccoli), carrots, pumpkins, palm oil

The role of vitamin A > Plays a role in mechanisms required for sight (11-cis retinal is the chromophore in the visual cycle) > Essential for growth and development > Required for healthy skin, epithelia and mucosa > Effects on certain endocrine glands > Important for fertility > Essential for proper immune functions β-Carotene: Provitamin A, biological antioxidant

Physical symptoms of vitamin A deficiency > Delayed growth and development > Night-blindness > Ocular lesions and xerophthalmia > Cutaneous lesions (dry and rough skin) > Impaired immune functions > Destruction of epithelial tissue (i.e. in lungs, intestines, urinary tract, genitals) Groups at risk of deficiency: > Pregnant and lactating women > Infants and young children > Populations suffering from poor nutrition (i.e. only rice, maize, potatoes as staple foods)

Fat-soluble

Vitamin

The prime natural sources of vitamin A

D

D2 Ergocalciferol D3 Cholecalciferol

Discovery of active ingredient: 1918 Isolation: 1932

Prime natural sources Animal products

Vegetable products

Oily fish | Egg yolk –> D3

Mushrooms –> D2

Animal products (main source for D3 ): Oily fish, egg yolk Plant products (main source for D2): Mushrooms Other: Synthesized in the skin by the action of ultraviolet light Vitamin D3 is superior to vitamin D2 in increasing and maintaining 25(OH)D serum levels

The role of vitamin D > Regulation of metabolism of calcium and phosphorus > Essential for normal bone development and maintenance > Plays a role in innate immunity by stimulating immune cells proliferation and cytokine production

Physical symptoms of vitamin D deficiency > Rickets in children > Osteomalacia in adults Groups at risk of deficiency: > Populations suffering from poor nutrition (i.e. only rice, maize, potatoes as staple foods)

Fat-soluble

Vitamin

The prime natural sources of vitamin D

E

Tocopherols and Tocotrienols

Main vitamin E activity: α-Tocopherol (Natural RRR- and all-rac α-Tocopherol) Discovery of active ingredient: 1922 | Isolation: 1936

Prime natural sources Animal products

Vegetable products

Dairy products | Eggs

Vegetable oils | Vegetables | Nuts

Animal products: Milk, butter, eggs Vegetable products: Vegetable oils, cereal germ, vegetables (i.e. spinach, lettuce, cabbage, avocados), nuts

The role of vitamin E > Biological antioxidant > Protects lipids (cell membranes), proteins, and DNA from oxidation and thereby contributes to cellular health > Assists fertility

Physical symptoms of vitamin E deficiency > Leads to destruction of red blood cells > Impaired immune function > Long-term impact includes neuromusclar diseases Groups at risk of deficiency: > Newborn babies, particularly premature > Individuals unable to efficiently absorb fats from the intestine

Fat-soluble

Vitamin

The prime natural sources of vitamin E

K

K1 Phylloquinone K2 Menaquinones

Discovery of active ingredient: 1929 Isolation: 1939

Prime natural sources   Animal products

Vegetable products

Dairy products | Meat | Liver

Green vegetables | Cauliflower

Animal products (main source for K2): Some dairy products (i.e. cheese & curd cheese), meat including liver Vegetable products (main source for K1): Green leafy vegetables (i.e. parsley, spinach), cauliflower Other: Fermented soybeans

The role of vitamin K > Essential anti-haemorrhaging agent (promotes blood clotting) > Helps to maintain bone health > Emerging evidence for potential role in cardiovascular health

Physical symptoms of vitamin K deficiency > Ecchymosis > Petechiae > Hematomas > Oozing of blood at surgical or puncture sites > In infants, birth defects such as underdevelopment of the face, nose, bones and fingers Groups at risk of deficiency: > Newborn babies (due to lack of intake)

Fat-soluble

Vitamin

The prime natural sources of vitamin K

B

1

Thiamine

Discovery of active ingredient: 1897 Isolation: 1926

Prime natural sources Animal products

Vegetable products

Offal | Fish | Meat

Cereals | Vegetables | Fruits | Pulses

Animal products: Offal (liver, kidneys, heart), fish, meat (porc) Vegetable products: Cereals, leafy vegetables, fruits (dried), pulses, nuts Other: Brewer’s yeast

The role of vitamin B1 > Energy metabolism (co-enzyme) > Essential for metabolism of carbohydrates, lipids, proteins (co-enzyme) > Required for proper functioning of the nervous system and muscles, which has implications for proper functioning of the cardiovascular system

Physical symptoms of vitamin B1 deficiency > Beriberi (still occurs in South-East Asia) Groups at risk of deficiency: > Alcoholics

Water-soluble

Vitamin

The prime natural sources of vitamin B1

B

2

Animal products: Offal (liver, kidneys, heart), eggs, meat, milk, cheeses Vegetable products: Cereals, vegetables Other: Brewer’s yeast

The role of vitamin B2 > Essential for the metabolism of carbohydrates, lipids and proteins (co-enzyme in many reactions) > General effect on tissues and organs (maintains health of mucosa) > Stimulates growth and reproduction > Plays a role in sight mechanisms > Conversion of vitamin (B6, folic acid and niacin) into their active co-enzyme forms

Physical symptoms of vitamin B2 deficiency

Riboflavin

> Skin and tissue membrane lesions (lips, tongue, fissures at corners of mouth) > Ocular symptoms (corneal vascularisation associated with sensitivity to bright light, impaired vision, itching) > Inflamed mucosal membranes

Prime natural sources

Groups at risk of deficiency: > Individuals whose food intake is unadequate > The elderly > Chronic dieters > Individuals who exclude milk products from their diet

Discovery of active ingredient: 1920 Isolation: 1933

Animal products

Vegetable products

Offal | Eggs | Meat | Milk | Cheeses

Cereals | Vegetables

Water-soluble

Vitamin

The prime natural sources of vitamin B2

B

3

Niacin; PP; Nicotinic Acid; Nicotinic Amide

Discovery of active ingredient: 1936 Isolation: 1936 Identification with nicotinic acid: 1937

Prime natural sources Animal products

Vegetable products

Offal | Fish | Meat

Cereals | Pulses | Fruits | Nuts

Animal products: Offal (liver, kidneys, heart), fish, meat Vegetable products: Cereals, pulses, fruit (avocados, figs, dates, prunes), nuts Other: Synthesized from tryptophan

The role of vitamin B3 > Required for the energy supply to all metabolic reactions in the body > Required for growth

Physical symptoms of vitamin B3 deficiency > Pellagra > Skin lesions > Digestive inefficiency > Insomnia > Fatigue > Loss of appetite Groups at risk of deficiency: > Chronic alcoholics > Individuals whose staple diet is maize or barley > Patients with Hartnup’s disease

Water-soluble

Vitamin

The prime natural sources of vitamin B3

B

5

Pantothenic Acid

Discovery of active ingredient: 1931 Isolation: 1938

Prime natural sources Animal products

Vegetable products

Offal | Meat | Egg yolk

Cereals | Nuts | Vegetables

Animal products: Offal (liver, kidneys), meat (chicken, beef), egg yolk, milk, fish Vegetable products: Cereals, nuts, vegetables (i.e. white mushrooms) Other: Synthesized by intestinal microorganisms

The role of vitamin B5 > Required for the synthesis of co-enzyme A and acyl carrier protein (ACP) > Key role in metabolism of carbohydrates, proteins and fats > Important for maintenance and repair of tissues and cells (skin, hair, and membranes) > Helps in healing of wounds and lesions > Pantethine (dimeric form of vitamin B5) normalizes blood lipid profiles

Physical symptoms of vitamin B5 deficiency > Nausea > Vomiting > Headaches > Tingling sensations (‘burning feet’ syndrome) Groups at risk of deficiency: > Individuals whose diet is lacking in the other B vitamins

Water-soluble

Vitamin

The prime natural sources of vitamin B5

B

6

Pyridoxine

Discovery of active ingredient: 1934 Isolation: 1938

Prime natural sources   Animal products

Vegetable products

Chicken | Liver | Fish

Nuts | Cereals | Bread | Vegetables

Animal products: Chicken, liver (cattle, pig), fish (salmon, tuna, sardines, halibut, herring) Vegetable products: Nuts (walnut, peanut), corn and whole grain cereals, bread, vegetables, fruit

The role of vitamin B6 > Required for the majority of biological reactions (i.e. amino acid metabolism, antibody production, neurotransmitter synthesis, red blood cell formation)

Physical symptoms of vitamin B6 deficiency > Deficiency of vitamin B6 alone is uncommon; usually it occurs in combination with a deficit in other B-vitamins > Poor growth > Kidney stones > Depression > General fatigue > Dizziness > Nerve problems > Irritability > Convulsions > Cutaneous lesions Groups at risk of deficiency: > Pregnant and breastfeeding women > The elderly > Underweight individuals > Alcoholics

Water-soluble

Vitamin

The prime natural sources of vitamin B6

B

7

Biotin; Vitamin H

Discovery of active ingredient: 1931 Isolation: 1935

Prime natural sources   Animal products

Vegetable products

Offal | Meat | Egg yolk

Vegetables | Cereals | Nuts

Animal products: Offal (liver, kidneys), meat (pork, mutton, poultry), egg yolk Vegetable products: Vegetables, cereals, nuts (walnuts, peanuts) Other: Synthesized by intestinal bacteria

The role of vitamin B7 > Involved in many cellular reactions > Intermediary metabolism of carbohydrates, fats and proteins, particularly in protein metabolism of hair roots and finger nail cells

Physical symptoms of vitamin B7 deficiency > Deficiency due to lack of dietary intake is rare > General fatigue > Nausea > Neurological problems > Poor skin and hair quality Groups at risk of deficiency: > Patients maintained on total parental nutrition > People who eat large amounts of raw egg white > Haemodialysis patients > Diabetes mellitus sufferers > Individuals receiving long-term anticonvulsant therapy

Water-soluble

Vitamin

The prime natural sources of vitamin B7

B

9

Folate (including folic acid and naturally occurring folates) Discovery of active ingredient: 1941 Isolation: 1941

Prime natural sources   Animal products

Vegetable products

Liver | Dairy products | Egg yolk

Leafy vegetables | Peanuts | Oranges

Animal products: Liver, dairy products, milk, egg yolk Vegetable products: Dark green leafy vegetables, beets, wheat germ, yeast, peanuts, oranges

The role of vitamin B9 > Required for the production of nucleic acids and in cell reproduction (i.e. red and white blood cells, nerve cells)

Physical symptoms of vitamin B9 deficiency > Tiredness > Loss of appetite > Fewer but larger red blood cells (megaloblastic or macrocytic anemia) > Weakness > Neurological problems > Digestive problems Groups at risk of deficiency: > The elderly (due to lower food intake) > Underweight people > Alcoholics

Water-soluble

Vitamin

The prime natural sources of vitamin B9

B

12

Cyanocobalamin

Discovery of active ingredient: 1926 Isolation: 1948

Prime natural sources   Animal products

Offal | Meat | Eggs | Fish | Dairy products

Animal products: Offal (liver, kidneys, heart, brain), meat, eggs, fish, dairy products

The role of vitamin B12 > Required for the formation of red blood cells to prevent anemia > Essential growth factor > Regeneration of folate > Involved in fat and carbohydrate metabolism > Essential for co-enzyme function, especially in cells of the nervous tissue, bone marrow and gastrointestinal tract

Physical symptoms of vitamin B12 deficiency > Pernicious anemia > General fatigue > Loss of appetite > Gastric atrophy > Neuromuscular pain > Neurological problems (gait, memory) Groups at risk of deficiency: > Vegetarians > The elderly

Water-soluble

Vitamin

The prime natural sources of vitamin B12

C

Ascorbic Acid

Discovery of active ingredient: 1912 Isolation: 1928

Prime natural sources Animal products

Vegetable products

Milk | Liver

Fruits | Vegetables | Lettuce

Animal products: Milk, liver (ox /calf) Vegetable products: Fruits (especially citrus fruits), vegetables, lettuce

The role of vitamin C > Multiple roles at a tissue and cell level (synthesis of collagen, absorption of iron, formation of carnitine and tyrosine) > Biological antioxidant (free radical scavenger) > Stimulates the body’s immune system: defenses against infections and inflammation

Physical symptoms of vitamin C deficiency > Scurvy (fatigue, loss of appetite and weight, lowered immune resistance to infections) Groups at risk of deficiency: > Smokers (active and passive) > Individuals with a low-vitamin diet

Water-soluble

Vitamin

The prime natural sources of vitamin C