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Excess Folic Acid During Pregnancy Harmful?

excess folic acid during pregnancy harmful

It is well accepted that it is important for pregnant women to get adequate amounts of folic acid to help prevent neural tube birth defects. However, excess folic acid during pregnancy could be harmful, based on new findings and some previous research.


What is the recommended amount of folic acid for pregnant women? According to the World Health Organization, 0.4 mg (400 micrograms; mcg) daily is the amount for healthy pregnant women.

The US Department of Health and Human Services recommends that all women of childbearing age (regardless of whether they plan to get pregnant or not) get 400 to 800 mcg daily. The general recommendation for women who have a family history of neural tube birth defects, however, is 4 mg (4,000 mcg).

New study on excess folic acid
But what if pregnant women take more than the recommended amounts? A new study published in the Journal of Endocrinology explored this question by conducting a rat study.

The animals were given 20 times their recommended daily amount of the vitamin throughout their mating, pregnancy, and lactation periods. At the end of the study, the researchers found that the babies of rat moms who received the excessive amount of folic acid developed into adults who were:

  • Overweight and insulin resistant
  • Deficient in a hormone called adiponectin, which protects against diabetes and obesity
  • Exhibiting abnormal feeding behavior

These symptoms were more striking in females than in males. In contrast, mother rats given the recommended amount of folic acid during mating, pregnancy, and lactation had babies that developed into healthy adults.

Although women around the world are urged to take folic acid, little research has been done to determine the safe upper limit. This is especially important since women may take supplements and also eat foods that are fortified with the vitamin, so the combination may boost their levels of folic acid into an unsafe category.

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Women may believe it is better to take more folic acid than what is recommended and do so on their own, without telling their doctor. A quick search on the internet revealed that supplements providing as much as 20,000 mcg (25-50 times the recommended amount) folic acid are available.

According to Professor Elisa Keating, the lead author of the study, “our study shows that it is possible to have too much of a good thing.” She also noted that “the search for a safe upper dose of folic acid is urgently needed.”

Folic acid, cancer and asthma
In an earlier study, scientists found that folic acid supplements taken in doses 2.5 to 5 times the recommended daily amount promoted the growth of existing pre-cancerous or cancerous cells in the mammary glands of rats. This finding is of some concern, according to Young-In Kim, a physician researcher at St. Michael’s Hospital and the study’s lead author, because in North America, breast cancer patients and survivors are exposed to high amounts of folic acid in fortified foods and through widespread use of vitamin supplements after diagnosis of cancer.

A recent study published in Pharmacoepidemiology and Drug Safety reported on the link between high intake of folic acid and asthma in children. The investigators used a database that contained pharmacy-dispensing information from 39,602 pregnancies.

The authors found that 2.9 percent of the 39,602 mothers were given high-dose (5 mg) folic acid and that these high doses were associated with an increased rate of asthma medication given to children. Based on these findings, the authors suggested that high-dose supplementation with folic acid during pregnancy may increase the risk of asthma in children.

Folic acid is an essential vitamin for overall health and also one that helps prevent neural tube defects in infants. However, it appears that too much of a good thing may be harmful for pregnant women, their children, and even women who have breast cancer. More research is needed in all of these areas to determine safe limits of folic acid.

Also read about how folic acid during pregnancy improves children's skills
Is folic acid good for autism?

Keating E et al. Excess perigestational folic acid exposure induces metabolic dysfunction in post-natal life. Journal of Endocrinology 2015; 224(3)
Manshadi SD et al. Folic acid supplementation promotes mammary tumor progression in rat model. PLoS ONE 2014; 9(1):
Zetstra-van der Woude PA et al. Maternal high-dose folic acid during pregnancy and asthma medication in the offspring. Pharmacoepidemiology and Drug Safety 2014 Oct; 23(10): 1059-65