Vitamins are needed for health, growth, and reproduction. Our bodies can not manufacture vitamins (apart from vitamin D) and they must be obtained in the diet.
Historical perspective
Long before vitamins were identified, certain foods were known to cure certain illnesses. The Egyptians, as well as the Ancient Greeks, treated night blindness with liver extracts and cooked liver. Today we know Vitamin A plays an important role in vision.
Many sailors suffered from scurvy during the fifteenth and sixteenth century as very few fruit and vegetables were available on these long sea voyages. In later times British scientists discovered that lime juice cured this disease and today we know vitamin C deficiency results in scurvy.Vitamins are categorised according to their solubility in fat or water. Solubility determines how vitamins occur in foods as well as their absorption, transport, storage and metabolism in the body.
Fat-soluble vitamins
Fat-soluble vitamins
The fat-soluble vitamins are vitamins A, D, E and K. Fat-soluble vitamins are transported by the same body mechanisms as fat. They are stored in the liver and fat tissues. Because excretion is minimal, excess intake can lead to toxicity.
Vitamin A
Vitamin A is present in food either as the vitamin (retinol) or as its precursor beta-carotene. Retinol is mainly found in animal products while beta-carotene is found in plant foods and is converted to vitamin A by the liver.
- Functions: Boosts immunity, helps prevent cancer, is necessary for healthy eye sight, normal growth and development
- Sources: Good sources of retinol include liver, fish-liver oils, cheese, butter, egg yolks. Good sources of beta-carotene include yellow vegetables (carrots, pumpkin), dark green vegetables (spinach, broccoli), sweet potato and orange coloured fruit (apricots, peaches)
- Deficiency: Poor vision, mouth ulcers, frequent infections, skin problems
Vitamin D
Vitamin D is synthesised by the body in the presence of sunlight (ultraviolet light). It must be obtained in the diet in the absence of sunlight. The amount of sunlight needed varies with skin colour and age. Dark-skinned people and the elderly need more exposure.
- Vitamin D is essential for absorption of minerals, vital for healthy teeth and strong bones and is required for kidney function
- Sources: Milk and dairy products, margarines, oily fish, fish-liver oils
- Deficiency: Rickets in children (soft bones), tooth decay, osteoporosis, osteomalacia
Vitamin E
Vitamin E (alpha-tocopherol) is an antioxidant, and has many other health benefits. Unlike most of the fat-soluble vitamins, up to 70% of intake is excreted. Heat, oxygen, freezing and food processing easily destroy this vitamin.
- Functions: Antioxidant, anti-aging, development and maintenance of nerves and muscles, builds immunity, improves fertility
- Sources: Wheat germ, soybeans, vegetable oils (sunflower, safflower oil), leafy green vegetables, eggs, oats, almonds, peanuts, seeds, margarine
- Deficiency: Muscle degeneration, breakdown of red blood cells, poor healing
Vitamin K
In 1935, the relationship between this compound and blood clotting was established. Little of this vitamin is stored in the body, but healthy gut bacteria ensure adequate amounts.
- Functions: Essential for blood clotting proteins, required for calcium metabolism
- Sources: Yoghurt, egg yolks, broccoli, Brussels sprouts, leafy green vegetables (cabbage, lettuce, spinach), liver, tomatoes, fish-liver oils
- Deficiency: Deficient blood clotting and bleeding, colon disease
Water-soluble vitamins
Water-soluble vitamins include B vitamins and vitamin C. As these are water-soluble they are and not stored in the body. They are easily destroyed during cooking due to heat and alkalinity.
B vitamins
The 8 vitamins in the B-complex group are essential for energy metabolism. Single deficiencies are rare because these vitamins occur together in nature. Alcoholics are at increased risk of B-complex deficiency.
- Thiamin (Vitamin B1)
Thiamin is necessary for the production of energy for brain, muscle, heart and nerve cells. It also promotes growth. Dietary sources include dried yeast, beans, whole grains, oatmeal, vegetables, milk, pork and liver.
- Riboflavin (Vitamin B2)
Riboflavin is necessary for energy metabolism and growth. Good sources include milk, liver, meat, leafy green vegetables, fish, broccoli and whole grains. Deficiency symptoms include sore mouth, lips and tongue as well light sensitivity.
- Niacin (Vitamin B3)
Niacin is vital for normal brain function and for energy and hormone metabolism. Liver and other meats, whole grains, peanuts, eggs, avocados and seeds are good sources. Niacin deficiency is known as pellagra, which is characterised by dementia, diarrhoea and dermatitis (dry, irritated skin).
- Pantothenic acid (Vitamin B5)
Pantothenic acid is the main component of co-enzyme A. This enzyme is involved in the synthesis of fatty acids and energy metabolism. Good sources include meat, whole grains, eggs, nuts and green vegetables (mushrooms, broccoli). Symptoms of deficiency include fatigue, loss of appetite, burning feet, skin disorders and weakness.
- Pyridoxine (Vitamin B6)
Vitamin B6 is essential in protein metabolism. Sources include avocados, bananas, fish and meats, whole grains, cabbage, potatoes, milk, eggs and seeds. Symptoms of deficiency include dry skin, tiredness and nervousness.
- Folic acid (folate)
Folic acid is necessary for healthy foetal development and the prevention of spina bifida (a congenital malformation of the spine). Low folic acid has also been linked to an increased risk of coronary heart disease and cancer. Good sources include leafy green vegetables, carrots, meats, whole grains, beans, oranges and asparagus. Folate deficiency is associated with poor growth, anaemia, birth defects.
- Cobalamin (Vitamin B12)
Vitamin B12 is involved in the metabolism of fatty acids and amino acids involved in nerve, blood and other cells. This vitamin is only present in animal products (meats, milk and dairy products and eggs). Vegetarians are therefore at risk for developing vitamin B12 deficiency. Symptoms of deficiency include anaemia, neurological (nerve) problems, fatigue and irritability.
- Vitamin C (Ascorbic acid)
Vitamin C plays an role in cell synthesis, cell protection (antioxidant), iron absorption and immunity. Good sources include citrus fruits (oranges, limes, grapefruit), pineapples, broccoli, tomatoes, cauliflower, green peppers, green vegetables and potatoes. Symptoms of deficiency include fatigue, sore gums and skin problems. Smokers have a much higher vitamin C requirement than non-smokers.
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