According to a report by the American Council On Science and Health, people hope or believe supplements will help prevent such diseases as cancer, heart disease, osteoporosis and age-related macular degeneration (a common form of blindness in the elderly).

Recent scientific evidence that taking supplements of specific nutrients such as vitamin C, vitamin E, beta-carotene, selenium, and calcium may be protective is not uniformly strong.

However, a diet rich in fruits and vegetables containing these nutrients can lower the risk of disease.

Every week, there's some new potion on the market with an exotic sounding name, or claims that you need to take almost toxic levels of vitamins to maintain a healthy lifestyle.

The theory that a vitamin is good for you, therefore the more you take, the healthier you'll be is illogical. Water is good for you. Drink too much and you may die. The sun is good for you. Again, too much sun and you can die. Vitamins and medicines are no different. In fact, some potions taken in conjunction with prescribed medicines can be extremely harmful and you should always check with the pharmacist or your GP if you're going to start supplements.

Let's look at the more common pills that are popped...

Vitamin A

Unless you have coeliac disease or cystic fibrosis, a deficiency of Vitamin A is rare in Western countires, as your liver stores enough supplies to get you through the months. It needs fats in the gut to be absorbed. A balanced diet containing dairy foods, eggs and fish should provide adequate amounts. Fruits and yellow and green vegies contain beta-carotene, which is converted to Vitamin A in the body (beta-carotene was thought to help prevent lung cancer but recent trials in the US were stopped after the incidence of lung cancer actually increased).

A normal adult diet supplies around 5000 units of Vitamin A per day (adult minimum is 2500 units, children 1000-2500 per day.). Taking unnecessary supplements can lead to chronic toxicity which causes vomiting, headache, scaly skin, hair loss, tender bones, enlarged liver, anaemia, cracked lips. It's worse for kids - arrested growth, headaches. Pregnant women can have malformed children.

Vitamin B6

Alcoholics or people who don't have a balanced diet may need B6 supplements, but outside that, there's no valid reason for popping extra pills. The recommended amount per day is 2.5 mg (50 mg during pregnancy). Taking over 100 mg per day can lead to nerve toxicity. Over 2000 mg per day will lead to toxic nerve damage.

Vitamin B12

Like Vitamin A, B12 is stored in the liver. Supplies come from animal products - meat, fish, eggs and milk. Supplements are usually unnecessary, although vegans may be deficient due to their strict diet.

Vitamin B12 in multivitamin tablets is not effective for treating a deficiency. It must be given by injection. B12 therapy was trendy as an energy booster, but anything over 1000 micrograms goes down the toilet!

Vitamin C

Ascorbic acid (vitamin C) does not cure colds or cancer, and we only need around 25-40 mg per day (more if you're pregnant, smoke, have an unbalanced diet or medical deficiency). Anything over that goes down the S Bend.

All vitamin C comes from what we eat - citrus fruit, blackcurrant juice, tomatoes, potatoes and greens are excellent sources. Taking high doses of C can actually create a dependency, as your body gets used to dealing with the extra load. If you suddenly stop taking vitamin C, the body still operates in "big load" mode and actually destroys C more quickly. Ironically, a condition called 'rebound scurvy' occurs. You may also be prone to kidney stones.

A recent study shows that mega doses of Vitamin C might actually speed up hardening of the arteries. Researchers from the University of Southern California studied 573 outwardly healthy middle-aged men and women. About 30 percent of them regularly took various vitamins. The study found no clear-cut sign that getting lots of vitamin C from food or a daily multivitamin does any harm. But those taking vitamin C pills had accelerated thickening of the walls of the big arteries in their necks. The more they took, the faster the buildup.

There was also a warning to cancer patients about the dangers of megadoses. It's thought large doses of the vitamin can actually protect tumours from radiation, chemotherapy and free radicals, as Vitamin C is an antioxidant.

Vitamin D

Sunshine makes our bodies produce vitamin D. Fish and dairy products contain small amounts. The only reason you may need D supplements is if you're housebound or have a medical problem.

There's no recommended daily dose as our bodies look after that department, however too much (over 4000 units per day over a few months) can cause elevated blood calcium accompanied by a nasty batch of symptoms ranging from headache to calcium deposits in ligaments and skin. Your bones will eventually weaken.

Vitamin E

Again, with a balanced diet containing oils, cereals and eggs, there should be no need for supplements. The daily recommended dose is 15 mg for men and women and 4-6 mg for children.

There's no evidence that vitamin E prevents heart attack, stroke, ageing or improves sexual function but there is some evidence that we may need small supplements due to inadequate intake. But this may be due to people underestimating how much fat they really consume. People on low fat diets may not get enough vitamin E, as with those who cannot absorb fat, such as cystic fibrosis and Crohn's disease sufferers.

Large daily doses can cause diarrhoea.

Source: The Australian Drug Guide by Dr Jonathan Upfal and Healthfraud.com; further sources: Office of Dietary Supplements.