Vitamin B12 (Cobalamin)
Vitamin B12 (B12) is an important nutrient during pregnancy, especially for the developing central nervous system, and some researchers compare its necessity during pregnancy to folic acid.
Although B12 deficiency is considered relatively common during pregnancy, it is unclear what effect this has on fetal growth or other pregnancy outcomes, but deficiency is easily treated with supplementation.
Women who do not eat – or rarely eat – animal products (meat, dairy, eggs) may be at risk for deficiency and will likely require B12 supplementation during pregnancy at the recommendation of their health care provider (HCP).
Supplementation likely has no effect for women who are not deficient, but it could potentially lower the risk of anemia and/or neural tube defects in high-risk women.
While interest in studying B12 during pregnancy has increased, this research is still relatively recent and overall, studies are limited. Women should talk to their HCP if they have any questions or concerns regarding their vitamin B12 status during pregnancy.
Background
Vitamin B12 (B12) is a water-soluble vitamin with roles closely related to folate (folic acid). It is important for normal cell division, red blood cell formation, energy production of cells, and the development of the central nervous system.
B12 is crucial for proper fetal growth, especially brain development. B12 assists in the creation of the myelin sheath (protective membrane) around the nerves in the brain so they function correctly.
Deficiency
B12 deficiency during pregnancy is common, and a 2016 review estimated 20% to 30% of pregnant women around the world are likely deficient (rates appear to be highest in India). However, it is not clear at what point a pregnant woman becomes "deficient" (likely different from the non-pregnant population).
In general, concentrations of vitamin B12 decrease from the first to the third trimester; the lowest concentration of vitamin B12 is seen around 32 weeks of pregnancy, but increases again prior to delivery.
While there is more to learn regarding B12 deficiency, it has been linked to miscarriage, preeclampsia, anemia, and preterm birth. It has also been reported that infants born whose mothers were B12 deficient may be at increased risk of neural tube defects, restricted growth, impaired motor function, and other neurological problems, which may be irreversible.
Deficiency in general (simple blood test) can cause numbness, tingling, difficult walking, swollen tongue, vision changes, fatigue, weakness, and problems thinking/remembering and trying to communicate.
Mild B12 deficiency can be corrected with a standard multivitamin, while a more severe deficiency can be corrected with weekly shots of B12 or daily high-dose B12 pills.
Medications such as proton pump inhibitors and antihistamines (which are commonly taken during pregnancy) reduce stomach acid, which may theoretically inhibit B12 absorption, which occurs directly through stomach acid. However, this research remains inconclusive.
Pregnant women with disorders such as Celiac disease and Crohn’s disease, or those who had gastric bypass surgery are also at high risk of deficiency.
Metformin, used to treat diabetes and other conditions during pregnancy, might reduce the absorption of B12.
Folate Relationship
Fetal growth causes an increase in the total number of rapidly dividing cells, which requires folate (natural form of folic acid). These cells help to create, form, and close the neural tube.
B12 sustains normal folate metabolism so that folate can do its job as required for cell division during pregnancy. Since folic acid supplementation does not prevent all NTDs, it is hypothesized that supplementation of B12 could reduce risk even further, but this has not yet been formally studied.
It is recommended that women take 400 to 1,000 micrograms (mcg)/day of folic acid before and during pregnancy, unless they are at high risk for NTDs, which may require a higher dose. High folate levels might mask B12 deficiency and worsen anemia.
The high prevalence of vitamin B12 deficiency during pregnancy, the rising popularity of vegetarian/vegan diets, and the increasing evidence that deficiency causes problems for both mother and baby, have ignited interest in mandatory food fortification with vitamin B12 (these programs already exist for folic acid and iodized salt).
Supplementation
It is currently recommended that pregnant women receive 2.6 mcg/day of B12 (compared to 2.4 mcg/day for non-pregnant women). It is likely that many women fall short of this recommendation during pregnancy, especially those who do not eat animal products.
The United Kingdom's Royal College of Obstetricians and Gynaecologists does not recommend routine supplementation of any B vitamin during pregnancy except for folic acid.
The American Dietetic Association recommends supplemental vitamin B12 for vegans and vegetarians during both pregnancy and lactation.
B12 supplementation during pregnancy is not expected to be harmful, and is likely necessary in some cases (no upper limit has been set); the body eliminates extra B12 through urine. However, high doses can cause dizziness, headache, anxiety, nausea, and vomiting. Women should talk to their health care provider before taking any vitamin supplementation during pregnancy.
Food Sources
B12 is obtained by eating animal source foods, including meat, fish, eggs, and dairy, specifically: trout, salmon, tuna, haddock, beef, milk, yogurt, and cheese. Additional foods, such as breads and/or cereals, may be fortified with B12.
Note: The U.S. Food and Drug Administration does not require food labels to list vitamin B12 content unless a food has been fortified with it.
Action
Women should talk to their HCP if they have any questions or concerns regarding their vitamin B12 status during pregnancy, to include whether they are considered high-risk for deficiency (vegans/vegetarians), neural tube defects, or anemia, or if they take certain medications that could decrease their body's ability to absorb B12 during pregnancy.
Resources
Vitamin B12 Fact Sheet (U.S. National Institutes of Health)