We need sufficient 5-MTHF to keep methionine synthase operating. Where does 5-MTHF come from? It's a form of folate that is produced by the enzyme methylene tetrahydrofolate reductase (MTHFR), and the gene that produces MTHFR has the same name. The body cycles through different forms of folate. Here's an illustration of that "folate cycle":
1 - A deficiency in total folate diminishes the amount of 5-MTHF that can be made from other forms of folate.
- Defective folate transport can result in autism spectrum disorders and other developmental disorders, and treatment with folinic acid (a form of folate) has been effective in in many children to reverse some autism symptoms. (https://www.ncbi.nlm.nih.gov/pubmed/26924398)
- An MTHFR polymorphism is associated with autism spectrum disorders in countries that do not fortify with folic acid.(http://onlinelibrary.wiley.com/doi/10.1002/aur.1300/abstract)
- Dr. Subit Barua at Columbia University and his colleagues have repeatedly observed autism-like effects in the brains of young mice whose mothers were fed high levels of folic acid during gestation. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4390789/, https://www.ncbi.nlm.nih.gov/pubmed/26547318, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4854024/)
- In May of 2016, Johns Hopkins announced having found that "if a new mother has a very high level of folate right after giving birth--more than four times what is considered adequate--the risk that her child will develop an autism spectrum disorder doubles." (http://www.jhsph.edu/news/news-releases/2016/too-much-folate-in-pregnant-women-increases-risk-for-autism-study-suggests.html) Because it's difficult to ingest excessive folate from unfortified foods (https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/), I think that the sources of excessively high folate levels in a pregnant woman in the USA are prenatal vitamin supplements, which typically contain folic acid (a relatively inexpensive form of folate), and processed food (particularly breakfast cereal) that has been fortified with folic acid.
Are we getting too much folic acid in the USA? I've come across articles about north American study populations that found unmetabolized folic acid in 40-95% of fasting study participants. (http://ajcn.nutrition.org/content/92/2/383.long, http://jn.nutrition.org/content/145/3/520.short) From that, I conclude that many in north America are definitely getting more folic acid than they need.
Am I anti-folate? Not at all. Every woman should take measures to ingest enough folate if she thinks she could become pregnant in order to lessen the risk of neural tube disorders such as spina bifida. But I think folic acid is a terrible form of folate to be putting in everyone's food and multivitamins. Folate is available in many foods naturally and in other supplement forms, including actual 5-MTHF.
**This is one of a series of posts. Here are the links to each entry in the series.**