Minerals and vitamins are an important part of the diet, but most of us don't realise our needs change as we get older. Dr Wynnie Chan explains which supplements are crucial during the different stages

Although 'meat 'n' two veg' used to sum up our approach to a wholesome diet, we now know that the body needs an optimum amount of vitamins and minerals to function efficiently and stave off disease. However, as you age, your body's needs change. Consequently, a 50-year-old's vitamin and mineral requirements are different from that of a 20-year-old. The following guide summarises what you should be eating to ensure good health - depending on your age.

In your 20s and 30s

1. Vitamin A
Why you need it: For growth, development and maintenance of healthy skin, as well as vision in dim light.
Recommended amount: 600 micrograms (mcg) per day for women between 19 and 50 years old.
How to get it:
There are two forms of vitamin A - retinol and carotenes (beta carotene is the most common form). Retinol is found mostly in animal foods such as milk, fortified margarine, butter, cheese, egg yolk, liver and oily fish like salmon, sardine, tuna and mackerel. Carotenes, which are converted to retinol in the body, are found mainly in plant foods such as carrots, tomatoes and dark green vegetables. The average British diet provides well above the required daily amount, which is equal to the following servings: 50g of boiled carrots; 125ml semi-skimmed milk; 50g boiled spinach; 100g mango.

Risks: A prolonged deficiency of vitamin A may lead to reduced night vision or night blindness, as well as a lowered resistance to infection. However, excessive doses of this vitamin can, over time, also be dangerous and toxic, as it accumulates in the liver; this is particularly risky for pregnant women as it may cause birth defects in unborn babies.

2. Folate (folic acid)
Why you need it: For the formation of healthy red blood cells.
Recommended amount: 200mcg per day for adult women.
How to get it: Folate - or its synthetic form, folic acid - is a vitamin found in small amounts in foods such as offal, yeast extract, green leafy vegetables and vitamin-fortified foods like bread and breakfast cereals. Most fruits, meat and dairy products contain little amounts of folate. Being a water-soluble vitamin, it is easily broken down in cooking or converted into a form that can't be used by the body. For these reasons, it's important to eat an adequate amount of food containing folate to prevent deficiency. Eating a 30g serving of fortified breakfast cereal, 90g serving of lightly boiled brussel sprouts and 72g (two slices) of brown bread a day will help you meet this daily requirement.

Risks: A deficiency can lead to megaloblastic anaemia (where red blood cells become enlarged) and can increase the risk of spinabifida, a neural tube defect in unborn babies where the brain or spinal cord fail to develop properly. Women planning a pregnancy are advised to take a 400mcg daily supplement of folic acid.

3. Iron
Why you need it: To make the compound haemoglobin in red blood cells - essential for carrying oxygen through the body.
Recommended amount: The suggested iron intake per day for women between 19 and 50 years old is 14.8mg.
How to get it: There are two forms of this mineral present in foods - haem and non haem iron. Haem iron, found in animal foods, is more easily absorbed by the body than non haem iron, which is found in plant foods. The absorption of non haem iron can be affected by other vitamins or minerals in the diet. For example, vitamin C increases iron absorption, while fibre, calcium and other compounds called phytates (present in cereals and pulses) and tannins (present in tea and coffee) prevent iron absorption. Red meat and offal are the richest sources of iron. Bread, breakfast cereals and other cereal products made from iron-fortified flour are also important sources, as are vegetables, eggs, lentils, potatoes and dried fruit. Your daily requirement can be achieved by eating any of the following: two slices of wholemeal bread; one bowl of cornflakes (fortified with iron); six dried apricots; one beef burger; one portion of lamb's liver.

Dangers: Prolonged iron deficiency leads to low iron stores in the body and eventually to iron deficiency anaemia. Large losses of blood due to injury or heavy menstrual periods will also cause a deficiency. It is possible to be iron deficient, yet have no clinical symptoms like anaemia. If you have this type of deficiency, it will affect your muscles' endurance and work capacity and can reduce your resistance to infection. Women in their 20s and 30s are most vulnerable to iron deficiency because of menstrual loss, a high prevalence of dieting (which tends to limit the types of foods consumed), and pregnancy or lactation.

4. Calcium
Why you need it: To form and maintain healthy bones and teeth, for proper functioning of the nerves and for blood clotting. This mineral is particularly important during times of growth, pregnancy and lactation.
Recommended amount: 700mg per day for women aged between 19 and 50 years old, with an additional 550mg during lactation.
How to get it: Calcium is found in milk and dairy products such as cheese and yoghurt. Bread, vegetables and canned fish with bones such as sardines or salmon are also important sources of calcium in the diet. The recommended daily amount can be met by drinking 250ml semi-skimmed milk, eating one small pot of yoghurt and one serving of canned sardines.

Risks: A calcium deficiency can lead to a disease called osteomalacia or decalcified bones (bones with little calcium). However, this disease usually results from too little vitamin D, which is required by the body to absorb calcium. Women who lose large amounts of calcium from repeated pregnancies and lactation may also suffer from a deficiency. In the long term, this may increase the risk of developing osteoporosis, a disease where gradual loss of bone density causes the bones to become brittle and break easily. Ensuring you get enough calcium at a young age helps to maximise bone strength and development.

In your 40s and 50s

1. Vitamin C
Why you need it: To make the protein collagen, which is required for forming healthy connective tissues and bone. Vitamin C also helps the body absorb iron and heal wounds. It is an important antioxidant, reducing the risk of heart disease and some cancers.
Recommended amount: 40mg per day for an adult woman
How to get it: Citrus fruits, blackcurrants, guavas, other tropical fruits and some vegetables are the richest sources of vitamin C. Milk provides this vitamin for people with very restrictive diets (those who eat mostly wholegrain cereals or who don't like fruit or veg). Potatoes are also an important source of this vitamin (although not rich in it) because they are a popular staple in the UK. Being water soluble, this vitamin is easily lost during cooking, so it's important to ensure you get an adequate amount of Vitamin C in your diet. The daily requirement can be met by eating 100g oranges or 20g blackcurrants or 450g boiled new potatoes.

Risks: Stress and smoking can lead to vitamin C being used up more quickly by the body. Deficiency can cause bleeding, particularly from small blood vessels under the skin and the gums; wounds also heal more slowly.

2. Vitamin D
Why you need it: For the absorption of calcium from the diet and maintaining healthy bones and teeth.
Recommended amount: 10mcg per day for adults over 50 years.
How to get it: There are few foods which contain significant amounts of this fat-soluble vitamin, so the most important source is from the sun via the action of UV light on the skin. Food sources include fortified margarine, oily fish, eggs, fortified breakfast cereals and meat or meat products. Because you can't measure how much Vitamin D you get via the sun, it's impossible to know exact food amounts that will help you meet the daily requirement. Eating foods from the above list, however, should ensure you get an adequate amount.

Dangers: Deficiency may be a problem for people who have a poor diet and for those who don't have adequate exposure to the sun. A deficiency can lead to pain, muscle weakness and osteomalacia.

3. Zinc
Why you need it: To help heal wounds and for the proper functioning of the immune system. Zinc is a component of more than 70 enzymes, and is required by the body to make and break down carbohydrates, fat, protein and DNA (genetic material).
Recommended amount: 7mg per day for women aged between 19 and 50 years old.
How to get it: This trace element is present in milk, cheese, meat, eggs, fish, wholegrain cereals and pulses. The daily recommended amount can be met by drinking 250ml milk, or eating any of the following: 90g stewed steak; 50g cheese; 75g ham; 72g wholemeal bread; 60g egg; 180g potatoes; 100g cod.

Risks: Zinc absorption is prevented by fibre and a high intake of phytates (compounds present in cereals and pulses). Although deficiency is rare, low levels of zinc will hinder the healing process and negatively affect the immune system and your ability to fight off infections.

4. Vitamin B12
Why you need it: To help form healthy blood cells and nerve fibres.
Recommended amount: 1.5mcg per day for women aged 19-50 years.
How to get it: The richest sources of vitamin B12 are offal and meat, although eggs, fish, milk and fortified breakfast cereals also contain it. Almost no plant foods contain this vitamin. The recommended daily amount can be absorbed by eating 30g fortified breakfast cereal and drinking 250ml milk.

Risks: Because vitamin B12 isn't found in vegetables, vegans who do not eat meat, milk or eggs may develop a deficiency. People in this age group who lack a chemical (called 'intrinsic factor') that helps carry Vitamin B12 from the stomach to the blood can be deficient as well. A deficiency leads to nerve damage and to megaloblastic anaemia.

It is important to remember that most people can meet their vitamin and mineral requirements by including a wide variety of foods in their diet. People under severe stress, those who are pregnant or on medication, and infants and young children may all need vitamin supplements. If you are concerned you're not getting an adequate amount of vitamins and minerals, consult a qualified health professional.