The research was carried out by a team from Queen Mary University London, Public Health England and Oxford University.
While 78 other countries to date have added folic acid to flour, the U.K. has not followed recommendations made several times over the last 15 years to improve levels of the important vitamin.
Last month government advisers wrote to ministers expressing concern that advice issued in 2000, 2006 and 2009 had not been followed.
Since 1998 more than 2,000 babies born in the U.K. have suffered serious birth defects of the brain, spine or spinal cord, reported BBC News. In some cases the babies died before birth; in others they died as newborns or experienced life-long disability.
Women trying to conceive are advised to take 400 micrograms of folic acid each day and to continue doing so during the first three months of pregnancy to reduce the risk of neural tube defects, such as spina bifida and anencephaly.
In the U.S. fortifying flour with folic acid has led to a 23 percent reduction in neural tube defects.
"Our results show that in the UK between 1998 and 2012, there was little, if any, change in the prevalence of pregnancies with a neural tube defect, while in the USA, quickly following the introduction of mandatory fortification of flour with folic acid in 1998, there was an approximate 23% reduction in the occurrence of affected births," said researchers. "Given the evidence from the Medical Research Council Vitamin Study regarding the efficacy of folic acid in preventing neural tube defects, the failure of Britain to fortify flour with folic acid has had significant consequences.
"The recent evidence that only 28% of pregnant women in England in 2012 took folic acid supplements at the correct time indicates that, in practice, recommending folic acid supplementation is largely ineffective (sic)."
Last month the Scientific Advisory Committee on Nutrition said it was in favour of folic acid being added to flour for bread in the U.K.
The Scottish government has urged U.K. ministers to take a quick decision on the issue in order to agree a uniform approach across the U.K. and the Department of Health said it was "considering the matter."
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