Vitamins and other food supplements taken by millions of women may actually put them at more risk, according to a major study.

Scientists say there is little evidence the pills do any good – and in fact some could be causing serious harm.

A study involving nearly 39,000 women has found multivitamins, vitamin B, folic acid, iron, magnesium and copper all increased the statistical risk of premature death.

Nearly a third of adults in Britain take some form of dietary supplement most days and the industry is worth ￡675million a year.

Some of the most popular pills include multivitamins, vitamin A, C and E, iron, folic acid and calcium – which are all thought to improve long-term health and ward off illnesses.

Scientists from Finland, Norway, the U.S. and South Korea looked at the long-term health effects of common vitamin pills and minerals on 38,772 women aged 55 to 69.

Over an 18-year period the women recorded any supplements they regularly took.

The results, published in the Archives of Internal Medicine, found copper increased the risk of dying prematurely by 18 per cent. Folic acid – which pregnant women are told to take to protect their child against spina bifida – increased risk of death by almost 6 per cent, while iron raised the risk by nearly 4 per cent.

Multivitamins raised the risk by 2.4 per cent, vitamin B6 by 4 per cent, magnesium by 3.6 per cent and zinc by 3 per cent.

The scientists do not fully understand how supplements may trigger early death, but they may interfere with the body’s natural defences. They say the supplements should only be taken by patients who are malnourished and only under the supervision of a doctor. Everyone else should ensure they eat a balanced diet to get adequate vitamins and minerals.

Jaakko Mursu, from the University of Eastern Finland, said: ‘Based on existing evidence, we see little justification for the general and widespread use of dietary supplements.

‘We recommend that they be used with strong medically-based cause, such as symptomatic nutrient deficiency disease.’

(Read by Nelly Min. Nelly Min is a journalist at the China Daily Website.)