Folic acid and asthma in children: best in early pregnancy?
|Article Type:||Clinical report|
Asthma in children
Asthma in children (Prevention)
Folic acid (Health aspects)
Pregnant women (Food and nutrition)
|Publication:||Name: Australian Journal of Medical Herbalism Publisher: National Herbalists Association of Australia Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2009 National Herbalists Association of Australia ISSN: 1033-8330|
|Issue:||Date: Winter, 2009 Source Volume: 21 Source Issue: 4|
|Geographic:||Geographic Scope: Australia Geographic Code: 8AUST Australia|
Whitrow MJ, Moore VM, Rumbold AR, Davies MJ 2009. Effect of
supplemental folic acid in pregnancy on childhood asthma: a prospective
birth cohort study. Am J Epidemiol Oct 30 (Epub ahead of print).
There have been several studies this year that have looked at the timing, dose and source of folate during pregnancy and its effect on childhood respiratory symptoms. This Australian study looked at data from an Australian prospective birth cohort study (n = 557) from 1998 to 2005. At 3.5 years and 5.5 years, 490 and 423 mothers and children respectively participated in the study. Maternal folate intake from diet and supplements was assessed by a food frequency questionnaire in early (<16 weeks) and late (30-34 weeks) pregnancy.
The primary outcome was physician diagnosed asthma obtained by maternal completed questionnaire. Asthma was reported in 57 (11.6%) of the children at 3.5 years and in 50 (11.8%) of the children at 5.5 years. At age 3.5 folic acid taken in supplement form in late pregnancy was associated with an increased risk of childhood asthma of about 26% and with a 32% increase in risk of persistent asthma. The association was similar at 5.5 years although this did not reach statistical significance in univariable models.
This suggests that the timing of supplementation in pregnancy is important. The findings show there is a potentially important critical period during which folic acid supplement dosages can be manipulated to optimise their neuroprotective effects while not increasing the risk of asthma. In this study supplemental folic acid in late pregnancy was associated with an increased risk of asthma in children, but there was no evidence to suggest any adverse effects if supplements were taken in early pregnancy.
The study supports these guidelines for use of folic acid supplements to reduce neural tube defects as it found no increased risk of asthma if supplements were taken in pre or early pregnancy. However the guidelines may need to be expanded to include recommendations about avoiding use of high dose supplemental folic acid in late pregnancy.
The two studies below, also published this year, give more insight into this relationship between folate and respiratory health although one seems to confirm the inverse relationship between folate levels and asthma while the other seems to indicate that folic acid supplements in the first trimester could be linked to a worsening of respiratory symptoms. Perhaps part of the answer is to consider the difference between folate and folic acid, the synthetic form of the vitamin as in the study above no links were observed between dietary folate and asthma risk.
Matsui & Matsui 2009. Higher serum folate levels are associated with a lower risk of atopy and wheeze. J Allergy Clin Immunol 123:6;1253-9 e2.
This study looked at the relationship between serum folate levels and markers of atopy, wheeze and asthma. Data from the 2005-2006 National Health and Nutrition Examination Survey was used in which serum folate and total IgE levels were measured in 8083 subjects 2 years of age and older. A high total IgE level was defined as greater than 100 kU/L. Allergen specific IgE levels were measured for a panel of 5 common aeroallergens, with atopy defined as at least 1 positive allergen specific IgE level. Doctor diagnosed asthma and wheeze in the previous 12 months was assessed by means of questionnaire. The results found that serum folate levels were inversely associated with total IgE levels, atopy and wheeze and this remained so even after adjusting for age, sex, race/ethnicity and poverty index ratio. The highest levels of folate were associated with a 16% reduction of asthma compared with the lowest levels.
Haberg SE et al 2009. Folic acid supplements in pregnancy and early childhood respiratory health. Archives of Disease in Childhood 94:3;180-4.
Considering that maternal intake of folate supplements during pregnancy might also influence childhood immune phenotypes via epigenetic mechanisms, this study looked at the relationship between folate supplements in pregnancy and risk of lower respiratory tract infections and wheeze in children up to 18 months of age. Using the Norwegian Mother and Child Cohort Study, questionnaire data collected at several time points during pregnancy and after birth on 32 077 children born between 2000 and 2005 was used to assess the effects of folate supplements during pregnancy on respiratory outcomes up to 18 months of age, while accounting for other supplements in pregnancy and supplementation in infancy. The results showed that folic acid supplements during the first trimester were associated with a 6% increase in wheezing, a 9% increase in infections of the lower respiratory tract and a 24% increase in hospitalisations for such infections.
Kim Hunter MNHAA
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