They are a daily essential for millions of people hoping to ward off ill-health, but vitamin pills do nothing for our health, according to a major study.
Researchers spent more than six years following 8000 people and found that those taking supplements were just as likely to have developed cancer or heart disease as those who took an identical-looking dummy pill.
And when they were questioned on how healthy they felt, there was hardly any difference between the two groups.
Experts said the study - one of the most extensive carried out into vitamin pills - suggested that millions of consumers may be wasting their money on supplements.
Many users fall into the category of the 'worried well' - healthy adults who believe the pills will insure them against deadly illnesses - according to Catherine Collins, chief dietician at St George's Hospital in London.
She said: "It's the worried well who are taking these pills to try and protect themselves against Alzheimer's disease, heart attacks and strokes.
"But they are wasting their money. This was a large study following people up for a long period of time assessing everything from their mobility and blood pressure to whether they were happy or felt pain.'
Multi-vitamin supplements have become increasingly popular as a quick and easy way of topping up the body's nutrient levels.
But a series of studies have indicated that, for some people, they could actually be harmful.
Two studies published last year suggested supplements could raise the risk of cancer.
One found pills containing vitamin E, ascorbic acid, beta-carotene, selenium and zinc increased the risk of malignant melanoma, the deadliest form of skin cancer, four-fold.
The other discovered women on a daily multi-vitamin pill increased their risk of breast cancer by up to 20 per cent.
While the evidence that vitamins can do harm is still limited, the latest study seems to confirm that many people are at the very least taking them unnecessarily.
A team of French researchers, led by experts at Nancy University, tracked 8112 volunteers who took either a placebo capsule, or one containing vitamin C, vitamin E, beta-carotene, selenium and zinc, every day for just over six years.
They assessed the state of their health at the beginning and end of the trial, taking a quality of life survey designed to measure everything from mobility and pain to vitality and mental health.
When researchers analysed how many in each group had gone on to develop serious illnesses over the years, they found little difference.
In the supplement group, 30.5 per cent of patients had suffered a major health 'event', such as cancer or heart disease.
In the placebo group, the rate was 30.4 per cent.
There were 120 cases of cancer in those taking vitamins, compared to 139 in the placebo group, and 65 heart disease cases, against 57 among the dummy pill users.
In a report on their findings, published in the International Journal of Epidemiology, the researchers said: 'The perception that supplementation improves general well-being is not supported by this trial.'
Miss Collins said the results of the study 'reinforce the idea that if you're worried about your health and start taking multi-vitamins, you will still be worried about it six years later'.
But the Health Supplements Information Service, which is funded by supplements manufacturers, said the finding that vitamins had no impact on how people perceived their health was 'to be expected'.
Spokeswoman Dr Carrie Ruxton said: 'The role of vitamin supplements is to prevent deficiencies and make sure people are receiving their recommended levels.
'They won't have a measurable impact on how you feel on a day-to-day basis but what they are doing is topping up your recommended levels to the right amount. They are not meant to be a magic bullet.'
- DAILY MAIL