Every day millions of people in Britain take vitamin supplements.
Vitamin C was thought to ward off colds
It is an industry that is worth £300 million a year, but the pills are surrounded by controversy.
Some people claim that by taking them in large doses, they will prevent or even cure illnesses like cancer and heart disease.
But others fear that taking large doses of some vitamins could in certain cases be dangerous.
"For most people there's absolutely no benefit in taking high dose vitamin supplements," said Catherine Collins, chief dietician at London's St George Hospital.
"At best they are a waste of money and at worst they could seriously affect your health."
Both sides of the argument are investigated in a Horizon documentary to be broadcast on BBC television on Thursday.
The huge popularity of taking large doses of vitamins can be traced back to one of the greatest scientists of the 20th Century, double Nobel prize winner, Linus Pauling.
He claimed that by taking large doses of Vitamin C, the equivalent of the amount found in hundreds of oranges you could prevent or even cure the common cold.
Many scientists accused him of quackery, but the public loved it.
Professor Pauling even claimed that huge doses of vitamins could help you live longer.
His work inspired a new generation of health advisors, who remain convinced that large doses of vitamins improves your health.
"I believe taking that vitamin supplements, not only adds years to your life, but also adds life to your years," said Patrick Holford of the Institute for Optimum Nutrition.
Vitamin C is the most popular vitamin sold in Britain, but was Linus Pauling right that it helps you fight the common cold?
Professor Balz Frei, the director of the Linus Pauling Institute, thinks that the latest scientific evidence reveals that Pauling was both right and wrong.
For the general population, taking large doses of Vitamin C does not to stop you catching colds - but it can relieve the symptoms and reduce the cold's duration.
Vitamin A has been linked to weakened bones
But lots of people take Vitamin C for a very different reason. It is one of a group of vitamins called anti-oxidants that are claimed to help prevent diseases like cancer or heart disease.
The idea comes from scientific studies that have shown that people who eat a diet rich in anti-oxidants, are less likely to develop these illnesses.
One explanation for this is that anti-oxidants can help prevent damage from harmful molecules called free radicals.
"Why we grow old is in part due to the activity of free radicals," said Professor Jeffrey Blumberg, of Tufts University Boston.
Vitamin E is one of the most popular anti-oxidant vitamin supplements on sale.
But earlier this year an American scientist warned that people could be missing the potential benefit of their supplements if they took them on an empty stomach, because the Vitamin E might not be absorbed properly without the presence of some of fat.
New research from King's College London, commissioned by Horizon, has investigated this idea further and yielded some surprising results.
The supplement they tested contained a tiny quantity of fat in itself and this seemed to be enough to enable the supplement to be absorbed.
Scientists are also still locked in debate about whether taking high doses of Vitamin C and E really can reduce your risk of chronic disease, but most safety experts agree that even in doses several times greater than the Recommended Daily Allowance (RDA), they are still relatively safe.
But in recent years there has been some worrying evidence emerging about a possible harmful effect of Vitamin A, even at quite low doses.
Research has shown that long term intakes of Vitamin A at around twice the RDA, may be linked to weaker bones and an increased risk of bone fracture.
The theory remains controversial, but if it's correct it means that people with high intakes of Vitamin A, either from food or the use of supplements may be slowly, silently weakening their bones.
Horizon: The Truth About Vitamins was broadcast on BBC Two on Thursday 16 September at 2100 BST.