Folic Acid During Pregnancy: What Is Too Much?

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Folate (also known as vitamin B9 or folic acid) is an essential vitamin important for the health of everyone, not just pregnant women. It is necessary to synthesize, repair and even methylate DNA. But are pregnant women getting too much?

1998: Mandatory Food Fortification

It should be mentioned that although folate and folic acid seem to be used interchangeably, there is a slight difference. Folic acid is the synthetic version of folate and is the compound found in prenatal supplements and food fortification.

Folate is mostly advertised to pregnant women for the prevention of neural tube defects as it is vital for the growth of the spine, brain, and skull of the foetus, particularly during the first four weeks of pregnancy (Antony, 2007). Several studies have confirmed the importance of folic acid in preventing neural tube defects (Bower, 2013; Cuskelly, McNulty, & Scott, 1999; Daly, Kirke, Molloy, Weir, & Scott, 1995; McNulty, Cuskelly, & Ward, 2000). Thus, since 1998, white flour, pasta and cornmeal have been fortified with folic acid in Canada (Allain-Doiron et al., 2014).

The objective of this fortification was to increase the average folic acid intake of women of childbearing age without exceeding the 1000 μg tolerable upper limit for the rest of the population (De Wals et al., 2007). Since the implementation of these recommendations, the overall prevalence of neural tube defects in Canada has decreased by 46% (De Wals et al., 2007).

Folic Acid Supplements

This is where it gets a little tricky. The Society of Obstetricians and Gynecologists of Canada (SOGC) recommends women take a supplement ranging from 400 μg to 1000 μg if they are at low risk for neural tube defects and up to 5000 μg of folic acid per day if they are at high risk (Wilson et al., 2007).

But can you guess what amount of folic acid is found in most prenatal supplements? The upper limit: 1000 μg.

High Folate Status in Pregnant Women

A study consisting of pregnant women from London, Ontario showed that the majority of women consuming dietary folate while taking a folic acid supplement consumed a mean daily intake of 2148 μg/day (Roy, Evers, & Campbell, 2012). Additionally, in a study of American pregnant women, median intake of folic acid was 1129 μg and intake of vitamins B2, B6, B12 and zinc were 1.3 to 5.5 times above the recommended amounts (Lagiou et al., 2005).

So, there is some evidence to suggest that consuming a well-balanced diet as well as a prenatal supplement can put you well above the tolerable upper limit. But does this do any real harm to pregnant women or to their offspring?

Too Much Folic Acid During Pregnancy

Concerns over the consumption of excess folic acid have been raised, as it may overpower the liver’s metabolic capacity (Obeid et al., 2010). In fact, a high dose (5000 μg) of folic acid intake over the first 12 weeks of supplementation nearly doubles the median plasma concentration of unmetabolized folic acid (Tam, O’Connor, & Koren, 2012). Additionally, high folic acid intake (>1000 μg/day) has been associated with adverse birth outcomes, specifically reduced birth weight and height (Pastor-Valero et al., 2011).

And remember how I said folate was involved in DNA methylation? Well, too much or too little folic acid intake during pregnancy may epigenetically affect the methylation of the offspring’s DNA, which can change gene regulation and expression. Thus, having long-term consequences on adult health.

 So… are pregnant women getting too much folic acid?

The takeaway message is that it seems like women who are consuming a balanced diet and taking a multivitamin containing more than 1000 μg of folic acid ARE exceeding the tolerable upper limit. Whether this has any effect on their health or the health of their offspring… the jury is still out.

Curious to learn about the effects of excessive folic acid on placental health and function? Check out this recently published University of Ottawa thesis.


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Flikr (Photographer). (2012). Pregnant woman [Photograph], Retrieved from:

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Pastor-Valero, M., Navarrete-Munoz, E. M., Rebagliato, M., Iniguez, C., Murcia, M., Marco, A., … Vioque, J. Periconceptional folic acid supplementation and anthropometric measures at birth in a cohort of pregnant women in Valencia, Spain. Br. J. Nutr, 2011;105(09): 1352-1360. doi:10.1017/S0007114510005143

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Tam, C., O’Connor, D., Koren, G. Circulating unmetabolized Folic Acid: relationship to folate status and effect of supplementation. Int J Gynaecol Obstet. 2012;485179–485195

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