Public consumption of folic acid from fortified flour at current mandated US levels (100micro-gram/day) and at double this amount is probably safe, at average intakes, according to an article published today in the open access journal BMC Public Health. The research has implications for the UK and Republic of Ireland, which plan to follow the US by adding folic acid to flour to help prevent neural tube defects in the near future.
Dr Mary Rose Sweeney and her colleagues from Trinity College Dublin commissioned a local bakery to bake three batches of bread, with different levels of folic acid. Single slices from the three batches contained 50micro-grams, 100micro-grams and 200micro-grams folic acid. The authors pre-saturated subjects first with daily 400micro-grams folic acid supplement, and subsequently tested them with a regime of two slices per day of the specially-prepared breads. Hourly blood tests determined whether folic acid was fully metabolised, and how long it remained in the blood.
Folic acid in bread at the 50micro-gram and 100micro-gram levels consumed twice with a 4-hour interval in between slices was fully metabolised each time. However a 400micro-gram supplement or 200micro-gram consumed once in a single slice of bread lead to metabolised folic acid in test subjects blood Long-term surveillance of the population is required to see whether folic acid accumulates, and to assess and potential safety implications.
Professor John Scott said: "this is good news in that it is possible to have optimum protection from a neural tube defect affected birth without having exposure to un-metabolised folic acid".
In fact the levels consumed currently in the US are thought to be in the range of 215-240micro-grams due to overage (the practice of adding a little extra to meet the mandate). Consumers may also get folic acid from other dietary sources, such as fortified cereals. The recommended dose for women of childbearing age in the UK is 400micro-grams per day.
Neural tube defects include spina bifida and anencephaly, which is fatal. Sufficient folic acid before and during pregnancy averts most neural tube defects. The neural tube develops in the first four weeks of pregnancy, often before many women know they are pregnant.
Article: Folic acid fortification and public health: report on threshold doses above which unmetabolised folic acid appear in serum
Mary Rose Sweeney, Joseph Mc Partlin and John Scott
BMC Public Health (In press)