Vitamin values

Often used as a winter pick-me-up or as a way of fighting seasonal bugs, vitamins are big business. People shell out thousands of euros a year on health supplements ? but it seems they could be doing more harm than good.

Millions of people could be overdosing on vitamins. Research into high-dose antioxidant supplements consistently shows either no benefit or an adverse effect. The safest advice is to look at the label on a vitamin supplement and aim for around 100 per cent of the recommended daily allowance (RDA).

For most of us, a balanced and varied diet provides us with all the nutrients we need but if you feel you're lacking, a multi-vitamin/mineral is the safest route if you do want to take a supplement because the chances are, if you are lacking in any vitamin or mineral in your diet, you are lacking in a range of vitamins rather than just one.

Higher doses of certain nutrients might benefit some people, such as folic acid, commonly used for pregnancy, Vitamin D for breastfeeding and infants under two years old and Vitamin B12 for strict vegans.

Following is some information on five of the most popular supplements:

VITAMIN A AND BETA-CAROTENE

Benefits: Healthy functioning of the eye and treatment of skin disorders.

RDA: 0.7mg for men and 0.6mg for women.

Dangers of over consumption: Where high doses have been taken over a long period of time, it is possible to have vitamin A poisoning. Symptoms are dizziness, nausea, headaches and vomiting.

Natural sources: Butter, eggs, liver, kidney, green vegetables, yellow/red fruits and yellow/orange vegetables. Carrots and tomatoes are best eaten cooked, rather than raw.

VITAMIN B6

Benefits: Improves disease resistance and maintains healthy skin and nerves to preventing premature aging. Many women find it helpful in dealing with painful periods, PMT and endometriosis.

RDA: 1.4mg a day for men and 1.2mg a day for women. Dangers of over consumption: Very large doses (more than 1,000mg) can cause poisoning and damage to the nervous system.

Natural sources: Found in green vegetables, fish, pulses, milk, liver, whole grain cereals, nuts, raisins and prunes.

VITAMIN C

Benefits: Maintains the strength of the walls of blood vessels and helps the body to absorb iron. Fights infection and diseases such as high blood pressure, arteriosclerosis and cancer.

RDA: 40mg for a healthy adult.

Dangers of over consumption: People may find that they have stomach problems with an intake of several grams a day. A sharp increase in vitamin C can cause diarrhoea.

Natural sources: Citrus fruit, berries, tomatoes, peppers, broccoli, cauliflower, potatoes, fresh green vegetables and chillies.

VITAMIN E

Benefits: Studies suggest taking this antioxidant lowers risk of heart disease and may reduce the risk of cancer and Alzheimer's.

RDA: 4mg a day for men and 3mg a day for women.

Dangers of over consumption: It is almost impossible to overdose on vitamin E. Some individuals find that doses in excess of 1g a day can cause stomach problems.

Natural sources: Wheatgerm, soya, corn and peanut oils, margarine, raw nuts and seeds, eggs, butter, yams, liver and some green leafy vegetables.

IRON

Benefits: Essential for the proper functioning of many enzymes, and the production of energy. The B vitamins cannot be metabolised without iron.

RDA: 4mg a day for men and 3mg a day for women.

Dangers of over consumption: Can interact with antibiotics and make them less effective in fighting infection. Too much can cause diabetes and liver failure when too much of the mineral is stored in the liver, spleen and endocrine glands.

Natural sources: Meat, liver, offal, blood, eggs, vegetables such as peas, parsley, green leafy vegetables, beetroot, pulses, nuts (almonds, particularly), apricots, figs, cocoa, whole grains and fortified flour and cereals.