Does Taking Folic Acid During Pregnancy Really Increase Risk for Child’s Asthma?

As a nutritionist and functional medicine doctor, I feel compelled to further comment on a recent study on folic acid following the article and video I released recently.  When you consider the serious impact of taking the form of folic acid that has shown to be a problem and the potential wrong conclusions that could easily be made regarding the recent study on folic acid, I trust that you will understand the value of the following comments.

A recent study on folic acid published in the American Journal of Epidemiology has caused quite a stir among pregnant women and their physicians recently.  If you only read a media summary of the findings, it appears to indicate that an essential nutrient, folic acid, taken by many pregnant women as a nutritional supplement, increases the risk for asthma in their offspring.

I have covered the forms of folic acid in my recent folic acid article. Here are the key points regarding the forms of folic acid:

  • Folic acid is the synthetic form while folate is the natural form.
  • Technically, the oxidized form of folic acid is called Pteroyl-L- Glutamic acid, which does not naturally occur in foods.  It happens to be the most stable for adding in food, thus, it is often used in fortifying foods with folic acid.  There is no naturally occurring biochemical reaction that utilizes this form.  It must be converted using a particular enzyme in order to be used in your body.  However, an estimated 33% of people are genetically deficient in this enzyme.
  • On the other hand, L-5-methyltetrahydrofolate (L-5-MTHF) is the naturally occurring form of folic acid.  Technically, this is called folate.  It naturally occurs in foods.  It is referred to as the active form because it does not need to be converted to another form for use in your body.

It is important to clearly understand these key points so that wrong conclusions are not made.

I will quote sections of the study, interpret it and put my comment below each quote.

“In early pregnancy, mothers were more likely to take folic acid as a standalone supplement than in late pregnancy (31% vs. 9%).  Stand-alone supplements contained a higher dose of folic acid than did multivitamins; that is, in early pregnancy, the median intake of folic acid from standalone supplement was 2,948 mcg/day compared with 500 mcg/day in a multivitamin.”

There is a high probability of problems whenever a person takes one specific nutrient supplement (1) without the consideration of the balance of other nutrients, (2) without an understanding of the synergistic effects of nutrients, (3) having the particular nutrient at a relatively higher dose, and (4) without consideration of the form of the nutrient.

“Dietary folate was not associated with asthma in either age group at any stage of pregnancy.”

Not surprising, because everything naturally occurring in foods is in the L-5- Methyltetrahydrofolate (folate) form.

”For every 100-mcg increase in dietary folate in early pregnancy, the relative risk of asthma for the child at 3.5 years decreased by 43% if the mother had asthma”

Not surprising;  DNA methylation is a very important process in early development of the brain, nervous system, respiratory tract and lungs.  Without sufficient folate you would expect increased problems especially in mothers with asthma.

”For child asthma at 5.5 years, significant interactions were found. For a 100-mcg unit increase in dietary folate in early pregnancy, the relative risk of the child’s having asthma at 5.5 years increased by 77% if the mother smoked during early pregnancy.”

This is to be expected due to oxidative damage.  Smoking greatly alters DNA and cell replication so you would need a great increase in all nutrients, including L-5-methyltetrahydrofolate (dietary folate) to offset the oxidative damage.  A 100 mcg increase in folate would not be enough to offset the oxidative damage from smoking.

”For every 1,000-mcg increase in folic acid in late pregnancy, the relative risk of the child’s having asthma at 5.5 years more than doubled if the mother had a previous child.”

This is reasonably to be expected because of oxidative damage to the mother’s DNA and the hormonal changes from pregnancy through the rigors of bearing a previous child. Using a synthetic folic acid rather than dietary folate predictably leads to problems with cell replication under this condition.

“For every 1,000-mcg increase in folic acid in late pregnancy, the relative risk of the child’s having asthma at 5.5 years decreased by 37% if the mother had asthma.”

This is the key sentence in the entire article! This is an expected effect.  With a pregnant woman with asthma, she should make sure to have a sufficient amount (1000mcg) of folate (not folic acid) even though the sentence says folic acid.  Some reasons  why it is protective for asthma and other atopic conditions (in relatively layman’s terms) in late pregnancy are:

  • forming cells (such as in an in-utero child) are highly susceptible to folate deficiency
  • folate, pyridoxyl-5-phosphate (active vitamin B6), and methylcobalamin (active vitamin B12) are critical in DNA synthesis and repair
  • DNA synthesis and repair occurs with a key process called methylation
  • inadequate methylation leads to chromosome breakage
  • folate is involved in making the methylation cofactor S-adenosylmethionine (SAM)
  • SAM deficiency is associated with congenital abnormalities
  • SAM deficiency is associated with increased oxidative stress
  • Asthma and atopic conditions are associated with increased oxidative stress
  • the mechanisms are discussed and additional scientific support for significant folate supplementation in pregnant women with asthma in this paper recently published by researchers at Johns Hopkins School of Medicine.

In a recent video, I briefly discussed the importance of using active forms of nutrients in prenatal vitamins.

The bottom line is: using the active forms of folate (found in real foods) and all nutritional supplements is always best.  But since just about everybody does not get all the necessary nutrients from foods alone, then everyone should supplement.  The key is getting supplements that have the active forms of the nutrients.

If you have any questions or comments regarding this article, post them here at  If you wish to visit us, my chiropractic and wellness clinic is in San Carlos, California, in the San Francisco bay area.


  1. Whitrow M, Moore V, Rumbold A, et al. Effect of supplemental folic acid in pregnancy on childhood asthma: A prospective birth cohort study.American Journal of Epidemiology 2009;170(10):1486-93.
  2. Matsui E, Matsui W.  Higher Serum Folate Levels are Associated with a Lower Risk of Atopy and Wheeze. J Allergy Clin Immunol. 2009;123(6):1253–9.