Britain's Food Standards Agency has decided not to recommend that folic acid is added to flour to reduce the risk of babies being born with defects like spina bifida, reports BBC Online.
The watchdog concluded at a meeting this week that more research was needed into the possible side-effects of fortification, according to the report.
The FSA is said to be particularly concerned that fortifying flour with folic acid may mask a deficiency of vitamin B12 in elderly people.
Results of a study currently taking place in Chile, where the mandatory fortification of folic acid to flour began in 2000, are however to be examined when released.
Adding folic acid to flour is recommended so that pregnant women receive adequate amounts, and therefore benefit from the vitamin's ability to reduce the risk of babies being born with neural tube defects such as spina bifida. And to have any benefit, folic acid must be taken before women conceive, notes the report.
It is estimated that only a third of women take folic acid supplements while they are trying for a baby, hence the advantages from introducing it into the national diet by adding it to flour.
The debate in Britain started in 2000, when the predecessor of the FSA, the Committee on Medical Aspects of Food and Nutrition Policy, said fortification of flour would prevent more than 70 children a year being born with defects.
However since then, both the Department of Health and research published last year in the British Medical Journal recommended further research on the matter.
Professors Brian Wharton and Ian Booth, from the Institutes of Child Health in London and Birmingham, warned that in people with vitamin B12 deficiency, consumption of folic acid may mask a condition called megaloblastic anaemia - which if not picked up can lead to degeneration of the spinal cord, according to the report.
Folic acid is also thought to interfere with some epilepsy drugs.
The FSA decision has been welcomed by the Consumers' Association which warned not enough was known about the risks of fortification of flour.
Sue Davies, principal policy officer for the Consumers' Association, said: "We welcome this decision. Now it's important that the Food Standards Agency and the Department of Health address the many issues that need to be researched before revisiting this subject."
"These include effective ways of monitoring possible B12 deficiency if folic acid were added to flour; the possible long-term effects of high doses of folic acid for the whole population; and the issue of choice: consumers would need an alternative if they don't want to eat fortified products," she told the BBC.