Initial Posting: 4/9/2017    Last Update: 5/16/2020
Answer: Prenatal vitamins can have too much folic acid, many do, and there is potential risk associated with this.
Folic acid is a synthetic form of the B vitamin folate(B9) which naturally occurs in foods, such as green leafy vegetables. Folate can help reduce the risk of your baby being born with spina bifida (a leading cause of childhood paralysis) and other birth defects. While most adults need 400 mcg DFE (Dietary Folate Equivalents) of folate daily, pregnant women need 600 mcg DFE. To be sure you get this, it's suggested that you take a supplement with 400 mcg DFE of folic acid and that you get the rest of your folate from your diet — from foods such as dark green leafy vegetables, oranges, and grain products enriched with folic acid.
Unfortunately, many prenatal supplements provide 800 mcg or more of folic acid — double the recommended amount from a supplement. That's not all. Folic acid is absorbed much better (about 70% better) than folate from foods. This means that a prenatal supplement with 800 mcg of folic acid gives you the equivalent of 1,360 mcg DFE of folate (but be aware that not all labels will reflect this change until 2021). On top of this, many manufacturers put in extra folic acid (30% or more is not uncommon), so it's quite possible that your supplement which lists 800 mcg of folate from folic acid is giving you the equivalent of about 1,800 mcg of folate.
The upper tolerable intake level (UL) for folate is 1,000 mcg, which only applies to synthetic forms, such as folic acid and methylfolate, found in supplements in fortified foods. It does not apply to folate found naturally in foods. Note that the UL is based on mcg and not mcg DFEs. Consequently, a product that contains 800 mcg of folic acid will not exceed the adult UL of 1,000 mcg folate, even though, nutritionally it provides about 1,336 mcg DFE. It's best not to exceed this because prolonged intake of excessive folic acid can cause kidney damage and can complicate the diagnosis of vitamin B-12 deficiency (folic acid supplementation can mask a symptom of vitamin B-12 deficiency). Of particular concern to pregnant women is that excessively high blood levels of folate (>59 nmol/L) in their blood was found to be associated with an approximate twofold increased risk of autism in their children according to an observational study in Baltimore in which 10% of women exceeded this level (Raghavan, International Meeting for Autism Research 2016). The study also found that when blood levels of both folate and vitamin B-12 were excessively high, the risk of autism was 17.6 times greater. (Note: Getting adequate folate during pregnancy may reduce the risk of autism; the concern is with getting too much).
In addition, one study found that taking 800 mcg or more of folic acid from supplements during the month before pregnancy through mid- pregnancy was associated with a 32% increased risk of gestational hypertension (high blood pressure in women during pregnancy).
So what should you do?
ConsumerLab.com has tested and compared many prenatal supplements and other multivitamins. Unfortunately, most on the market tested by CL to-date have too much folic acid (more will be tested in mid-2017). For now it may be safest to skip a "prenatal" vitamin with 800 mcg of folic acid and, instead, choose a daily multivitamin which provides 400 mcg of folic acid. The multi should also provide other nutrients of particular importance during pregnancy such as iodine (150 mcg), vitamin D (600 IU), and calcium (1,000 mg per day is the daily requirement, but don't take more than 500 mg at a time from a supplement). A challenge, however, is getting adequate iron, since the daily requirement during pregnancy (27 mg) is higher than for other pre-menopausal women (18 mg). A women's multi can provide all the nutrients listed above, but typically just 18 mg of iron, so you'll need to get extra iron from your diet. Alternatively, you can choose another multi and take a separate iron supplement providing about 27 mg of iron.
Your Prenatal Vitamin Needs a Check-up with CL founder, Dr. Tod Cooperman