By JENNY HOPE

Last updated at 22:53 30 October 2007

Adding folic acid to bread supplies may significantly damage the nation's health, food scientists have warned.

A plan to fortify flour with the B vitamin in a bid to reduce birth defects could backfire by increasing cases of bowel cancer and trigger problems for people with leukaemia and arthritis.

But it might take 20 years before the effects of increased consumption by millions of people become known, says the Institute of Food Research.

The IFR's warning will fuel debate over whether the benefits of fortifying flour with folic acid outweigh the health risks.

It comes as the Food Standards Agency has in principle approved putting folic acid in bread flour, although Government ministers have yet to make the final decision.

By boosting the diets of pregnant women, it would cut the rate of defects such as spina bifida in the unborn baby which can cause serious disability.

However, research has suggested the human body might struggle to break down folic acid in even half the amounts proposed for supplementing foods.

That would mean two slices of fortified bread a day every day could be a danger to those at risk.

While the institute said pregnant women continue taking folic acid supplements, it warned that in the future just two slices of fortified bread a day every day could lead to problems in people who are not deficient.

In the UK, women trying to conceive and in the early stages of pregnancy are recommended to take supplements to prevent birth defects.

Most breakfast cereals are already fortified here, while the recommended dose for anyone wanting to top up low levels is 200 micrograms a day.

Dr Sian Astley from the IFR said: "Fortifying UK flour with folic acid would reduce the incidence of neural tube defects.

"However, with doses of half the amount being proposed for fortification in the UK, the liver becomes saturated and unmetabolised folic acid floats around the blood stream.

"This can cause problems for people being treated for leukaemia and arthritis, women being treated for ectopic pregnancies, men with a family history of bowel cancer, people with blocked arteries being treated with a stent and elderly people with poor vitamin B status.

"This has important implications for the use of folic acid in fortification, because even at low doses it could lead to over-consumption, with its inherent risks."

She said it also increased the likelihood of multiple births for women undergoing fertility treatment.

Folic acid is the synthetic form of folate, a B vitamin, found in leafy green vegetables, cereals and fruit.

A paper published in the British Journal of Nutrition found folic acid is broken down by the liver, whereas natural folates are broken down in the stomach.

Scientists claim a liver flooded with folic acid may end up releasing it undigested into the blood.

Excess levels of folic acid in the blood have been linked to bowel and breast cancer, and could accelerate brain decline in some elderly people.

The scientists said the full impact of putting folic acid in food may only become apparent in 20 years' time.

There has been ongoing concern about the impact of mandatory fortification of bread flour on elderly people with B12 deficiency, but IFR scientists say an even broader range of people could be at risk.

Dr Astley said there had been a long-held assumption that folic acid was digested in the same way as naturally- occurring folates, but this appeared to be wrong.

"We challenge the underlying scientific premise behind this consensus. The FSA came to a carefully considered verdict but this field of research has moved on extraordinarily fast, and it would be irresponsible of us not to make our findings public."

Dr Astley said 13million Britons did not eat enough folate, which could equally put them at risk of health problems, and as many as 900 pregnancies a year are affected by birth defects for the same reason.

"It's a complicated and confusing issue. We want to encourage those who don't eat enough to increase their intake, but we don't want people eating too much in a sledgehammer approach to fortification.

"We have to work out the groups it might be helpful for," she added.

It has been added to bread, flour, cereals, pasta, rice and other grains in the U.S. since 1998. There has been a fall in the number of folate-deficiency birth defects, but there are concerns it might be causing a rise in bowel cancers.