Is there a Link Between Maternal Folate Exposure and Asthma?
Folate is an essential nutrient for everyone, and particularly expectant mothers. Folate deficiency is associated with increased risk of major congenital abnormalities such as spina bifida. Folate has various roles in the body: the formation of red blood cells, DNA formation and repair, amino acid metabolism. Folate also influences epigenetic programming and the immune system. The role of folate in the development of childhood allergy including asthma focuses on these last two points. In the latest issue of Nutrition Reviews, Brown, Reeves and Bertone-Johnson summarize the current evidence on folate status during pregnancy and the later development of asthma.
The incidence of childhood asthma has increased in recent decades, generally affecting 5% to 20% of children in countries around the world according to an international review from Asher and co-workers, and is a concern as it can have a serious effect on quality of life for those affected. Asthma is one of three parts of an allergic sensitization triad that includes seasonal or food allergies, and eczema, and reflects a state of hypersensitivity of the immune system. How folate directly affects the development of asthma is still being researched, however it seems that changes in DNA methylation patterns could cause excess production of regulatory T and Th cells, which are linked to asthma (see Virchow’s review).
Various studies have looked at whether there is epidemiological evidence of a link between folate status in pregnancy and asthma. One complicating factor is the effect of folate fortification and supplementation on the folate status of pregnant women. Supplemental folate has a greater bioavailability than that found naturally in foods. Nutrient databases must be updated to reflect greater provision of folate after fortification, and this may impact some of the research in countries that have fortified the food supply in the past few decades.
After a careful review of the evidence, the authors did not find a link between folate intake and childhood asthma. Although some studies have shown a positive association, some methodological problems may have affected the results. The few studies that found a link between folate intake in pregnancy and asthma in childhood have found it to be transient. Timing may be important, however. High folate exposures in late pregnancy, compared with early pregnancy when it is most critically needed, has been more consistently associated with asthma risk.
The authors highlight that the prevention of neural tube defects is a more important outcome than potential risk of a transient increase in asthma incidence.
Brown SB, Reeves KW, Bertone-Johnson ER. Maternal folate exposure in pregnancy and childhood asthma and allergy: a systematic review. Nutrition Reviews. 2013:n/a-n/a. http://onlinelibrary.wiley.com/doi/10.1111/nure.12080/abstract
Asher MI, Montefort S, Björkstén B, Lai CK, Strachan DP, Weiland SK, Williams H; ISAAC Phase Three Study Group. Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC Phases One and Three repeat multicountry cross-sectional surveys. Lancet. 2006 Aug 26;368(9537):733-43. http://www.ncbi.nlm.nih.gov/pubmed/16935684
Virchow JC. Asthma and pregnancy. Semin Respir Crit Care Med. 2012 Dec;33(6):630-44. doi: 10.1055/s-0032-1326961. Epub 2012 Oct 9. http://www.ncbi.nlm.nih.gov/pubmed/23047313