The role of vitamin B12 in the prevention of neural tube defects

2nd July 2024


The role of folate/folic acid in supporting brain and spine development and helping to prevent neural tube defects is relatively well known, though the need to take supplements at least 2-3 months before trying to conceive is not as widely, nor as clearly, publicised. The importance of B12 is even less well known but has been promoted by Shine since 2012 and is now recognised by the NHS and NICE.

Vitamin B12 and folate are B vitamins that work together to help build DNA for new cells. They are critical for growth and repair in the body. Folate and B12 are important in building the brain and spine in developing babies. Specifically, they are involved in the development of the poppy seed-sized structure called the neural tube. During the first four weeks of pregnancy, the neural tube is created from a sheet-like structure that folds over and “zips up” to form a tube. This tube eventually forms the brain and spinal cord. Cells divide and grow very quickly during early pregnancy, and extra folate and B12 are needed to make DNA for the new cells. Neural tube defects such as anencephaly and spina bifida occur when the neural tube fails to fully close, leaving a gap. Nerve tissue is exposed through the gap and becomes damaged as the pregnancy progresses. Not having enough folate and/or B12 has been shown to increase the chance of neural tube defects occurring during pregnancy.

If you are thinking of having a baby, alongside 400 mcg of supplemental folic acid, you should ideally take 2.5 mcg of B12 daily for three months before trying to conceive. Some groups of people should consider asking the GP to check their B12 levels before trying for a baby; this includes people with stomach conditions (including gastric surgery, reflux treated with medication to control stomach acid); conditions affecting intestinal absorption (e.g. inflammatory bowel disease); personal or family history of pernicious anaemia; vegetarian/vegan diet. We would also recommend this includes those taking metformin.

Metformin is a medicine used to treat and prevent type 2 diabetes and gestational diabetes. It lowers blood sugar levels by improving the way the body handles insulin. Metformin is also sometimes used "off-label" to help manage blood sugar levels in women with polycystic ovarian syndrome (PCOS). By lowering insulin and blood sugar levels, metformin can encourage ovulation and improve the regularity of periods. Poorly regulated blood sugar levels are known to increase the chance of neural tube defects, so if you’re planning a family, it’s particularly important to manage your diabetes well, as directed by your healthcare professionals.  The MHRA recently issued a Drug Safety Update for Metformin showing that 1 in 10 people will become deficient in B12 as a result of taking the medication. The update doesn’t mean you should stop taking metformin if you are trying to conceive, on balance the benefits of the medication outweigh the possible risks. However, people who are taking Metformin may benefit from having their B12 levels tested before trying to conceive. It is important not to stop taking any medication without consulting your prescribing clinician, and it is worth noting that the UK Technology Information Service states, “The available data do not show an increased risk of congenital malformation, spontaneous abortion, preterm delivery, small or large for gestational age infants, perinatal mortality or neonatal complications. However, there is insufficient data relating to metformin exposure in early pregnancy to exclude an increased risk of congenital malformations or spontaneous abortion. NICE guidance states that women with diabetes may be advised to use metformin as an adjunct or alternative to insulin in the preconception period and during pregnancy when the likely benefits from improved blood glucose control outweigh the potential for harm.”

In summary, B12 is an important vitamin with a little-known role in developing the brain and spine in early pregnancy. We recommend that anyone planning a family take B12 and folic acid supplements three months before starting to try to conceive, and those at risk of deficiency should ask their GP for a blood test of their B12 levels.


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