Intakes of folic acid from enriched cereal-grain products, ready-to-eat cereals, and supplements do not lead to excessive intakes of the B vitamin, according to a study that may allay the fears over folic acid build-up, and weaken the arguments of anti-fortification groups around the world.
“At current fortification levels, US adults who do not consume supplements or who consume an average of 400 micrograms folic acid/d from supplements are unlikely to exceed the upper limit in intake for folic acid,” wrote the researchers in the American Journal of Clinical Nutrition.
Robert Berry from the Centers for Disease Control and Prevention and his co-workers analysed data from 8,258 participants of the National Health and Nutrition Examination Survey (NHANES) 2003 to 2006.
B for baby benefits
An overwhelming body of evidence links folate deficiency in early pregnancy to increased risk of neural tube defects (NTDs) - most commonly spina bifida and anencephaly - in infants.
This connection led to the 1998 introduction of public health measures in the US and Canada, where all grain products are fortified with folic acid - the synthetic, bioavailable form of folate.
Preliminary evidence indicates that the measure is having an effect with a reported 15 to 50 per cent reduction in NTD incidence. A total of 51 countries now have some degree of mandatory fortification of flour with folic acid.
However, similar measures in other countries have been opposed by concerns that the folate/folic acid may mask vitamin B12 deficiency, which leads to a form of neurological problems.
Concerns over B12 and bowel health
The results of the new study found however, that consumption of the ready-to-eat cereals and/or supplements with folic acid was actually associated with higher than usual vitamin B12 intakes.
Opponents of folic acid fortification also point to studies raising concerns about increased risks of colorectal cancer. Epidemiological evidence suggests a slight increase in colorectal cancer rates following the introduction of fortification. Such associations have been noted in the US, Canada, and Chile.
According to Joel Mason from USDA Human Nutrition Research Center on Aging at Tufts University, high folate levels in certain people who harbour pre-cancerous or cancerous tumours may actually promote cancer.
The complex links between folate and cancer have created a “global dilemma”, he said. Indeed, a new study published in the Proceedings on the National Academy of Sciences (PNAS) shows that our ability to convert folic acid to folate may be relatively slow, leading to extended exposure to unconverted folic acid.
The new study, however, challenges such arguments by showing that less than 3 per cent of the study population exceeded the tolerable upper level of 1,000 micrograms a day.
Of the 60 per cent of the study participants who consumed folic acid from foods only, none exceeded 1,000 micrograms, report the researchers.
Furthermore, of the 34 per cent of the study participants who consumed supplements with 400 micrograms per day of folic acid or less, less than 1 per cent exceeded 1,000 micrograms.
“Because the vast majority of RTE and supplements with folic acid also contain vitamin B12, consumption may reduce the risk of vitamin B12 deficiency among older adults,” wrote Berry and his co-workers.
“[Previous studies and] our data suggest that US adults aged at least 60 years old who do not consume supplements with vitamin B12 may be at increased risk of vitamin B12 deficiency, even those with median usual vitamin B12 intakes of about 3 micrograms per day from RTE (greater than the Recommended Dietary Allowance of 2.4 micrograms per day),” they added.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi:10.3945/ajcn.2009.28401
“Folic acid source, usual intake, and folate and vitamin B-12 status in US adults: National Health and Nutrition Examination Survey (NHANES) 2003-2006”
Authors: Q. Yang, M.E. Cogswell, H.C. Hamner, A. Carriquiry, L.B. Bailey, C.M. Pfeiffer, R.J. Berry