Vitamin A (retinol)

Sources

Vitamin A is found in liver, kidney, milk, eggs, butter and margarine. It can also be produced in the body from its precursor, beta carotene, which is found in green vegetables and in red/orange coloured foods such as peaches, carrots and apricots.

Main functions

• helps to maintain healthy skin, teeth and bones, as well as mucous membranes in the nose, throat and lungs
• increases resistance to infections and helps promote healing
• required for production of a pigment in the eye needed for vision at night and in dim light
• essential for proper foetal development, but excessive intake may lead to congenital defects
• beta carotene may also reduce the level of free radicals, highly reactive chemicals generated in the body that can cause damage to cells

Results of deficiency

Vitamin A deficiency can result in increased susceptibility to respiratory tract infections, skin disorders and dry eyes (xerophthalmia). With severe deficiency there can be physical changes to the eye, leading to night blindness and, ultimately, total blindness.

Recommended intake

Lactation

intake (m g/day)

950

Who may benefit from supplements

• vegetarians, retinol is only found in animal products, although the precursor beta carotene is found in plant tissue
• diabetics, who may be unable to convert beta carotene to retinol efficiently
• people who have problems absorbing fats, or with other disorders of absorption
• In addition:
• low intakes of beta carotene have been associated with an increased risk of cancer and heart disease
• beta carotene supplements can help protect the skin from prolonged exposure to the sun

Precautions

Vitamin A supplements should not be taken with acne products derived from vitamin A. Vitamin A requirements are reduced in women taking the contraceptive pill.

Vitamin D (calciferol)

Sources

There are two forms of vitamin D, cholecalciferol (vitamin D3) which is found in animal products and ergocalciferol (vitamin D2) which is found in plant tissue. Fish are a particularly good source of vitamin D. Other dietary sources include dairy products, eggs and liver. The body produces vitamin D itself when skin is exposed to sunlight.

Main functions

• regulation of calcium/phosphorus absorption and metabolism
• needed for healthy growth of teeth and bones

Results of deficiency

In children, vitamin D deficiency can result in the twisted and malformed limbs associated with rickets. The growth of teeth may also be delayed. The adult equivalent of rickets is osteomalacia, in which bones are brittle and painful. There may also be muscular spasms.

Recommended intake

Lactation

intake (m g/day)

10

As vitamin D is principally needed for bone and tooth development, children generally have a higher requirement than adults. In people over 3 years of age, vitamin D produced by exposure of the skin to sunlight is generally sufficient to meet the body’s needs.

Who may benefit from supplements

• vegetarians and vegans, as vitamin D is mostly found in animal products
• people from cultures where dress customs limit exposure to sunlight
• housebound people
• women in whom several pregnancies have depleted their body’s store of calcium
• breast-feeding women, as babies need calcium to build bones and teeth

Precautions

Vitamin D is potentially the most toxic of all the vitamins, and excessive amounts can damage the kidneys, heart and lungs. Care should be taken not to exceed the recommended dose, although vitamin D is safe at up to five times the recommended intake.

Vitamin E (tocopherol)

Sources

Good sources of vitamin E include seeds, vegetable oils, wholegrain cereals and nuts.

Main functions

• vitamin E is a powerful antioxidant, and so helps to lower the levels of free radicals
• it is needed for the production of healthy red blood cells and skin
• it may also have other activities, such as reducing the risk of thrombosis and anti-clotting properties – the exact role of vitamin E in the maintenance of good health is not clearly established

Results of deficiency

Vitamin E is widely available in food and deficiency is rare, but can occur due to problems with absorbing food or restricted diets. Symptoms include muscle wasting, nerve damage, anaemia and reproductive problems.

Recommended intake

The requirement for vitamin E is dependent on the amount of polyunsaturated fatty acids in the diet. As this varies from person to person, there is no single recommended nutrient intake for vitamin E. In the USA, guidelines suggest an intake of 0.4mg/g of polyunsaturated fatty acids per day. For a typical diet, this is equivalent to around 5–7mg of vitamin E per day.

Who may benefit from supplements

• people with cardiovascular problems, who may benefit from the effects on the blood
• anyone who has had surgery, as it may assist the healing process
• smokers, as smoking increases the number of free radicals in the body

Precautions

People taking anticoagulant medicines should consult their doctor before taking vitamin E supplements, and diabetics are generally advised not to take them. Vitamin E is believed to be free from side effects at doses up to 3,200 mg/day. Fatigue, nausea, hypertension and gastro-intestinal problems have been associated with excessive levels, but these effects are usually reversed when the levels are reduced. The mineral, selenium, can increase vitamin E activity and vice versa.

Vitamin K (acetomenapthone)

Sources

Vitamin K is found in leafy green vegetables and egg yolk, and is also made by bacteria present in the human intestine

Main functions

• promotes coagulation of blood
• assists in the formation of the enzyme prothrombin which produces fibrin, a protein involved in the clotting of blood

Results of deficiency

• bleeding problems in new-born babies and people taking anticoagulants

Who may benefit from supplements

• new born infants
• people taking anticoagulants
• people with obstructive jaundice, as Vitamin K can only be absorbed in the presence of bile