Is Folate Status a Risk Factor for Asthma or Other Allergic Diseases?
OBJECTIVE
It is controversial whether folate status is a risk factor for the development of asthma or other allergic diseases. This study was conducted to investigate whether indirect or direct exposure to folate and impaired folate metabolism, reflected as methylene-tetrahydrofolate reductase (MTHFR) C677T polymorphism, would contribute to the development of asthma and other allergic diseases.


METHODS
Electronic databases were searched to identify all studies assessing the association between folate status and asthma or other allergic diseases. Two reviewers independently assessed the eligibility of studies and extracted data. The relative risk (RR) or odds ratio (OR) with 95% confidence intervals (CI) was calculated and pooled.


RESULTS
Twenty-six studies (16 cohort, 7 case-control, and 3 cross-sectional studies) were identified. Maternal folic acid supplementation was not associated with the development of asthma, atopic dermatitis (AD), eczema, and sensitization in the offspring, whereas exposure during early pregnancy was related to wheeze occurrence in the offspring (RR=1.06, 95% CI=[1.02-1.09]). The TT genotype of MTHFR C677T polymorphism was at high risk of asthma (OR=1.41, 95% CI=[1.07-1.86]).


CONCLUSIONS
It is indicated that maternal folic acid supplementation during early pregnancy may increase the risk of wheeze in early childhood and that the TT genotype of MTHFR C677T polymorphism impairing folic acid metabolism would be at high risk of asthma development. These results might provide additional information for recommendations regarding forced folate consumption or folic acid supplements during pregnancy based on its well-established benefits for the prevention of congenital malformations. However, currently available evidence is of low quality which is needed to further elucidate.
Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu 610041, PR China.
Ting
T
Wang
Pneumology Group, Department of Integrated Traditional Chinese and Western Medicine, State Key Laboratory of Biotherapy of China, West China Hospital, Sichuan University, Chengdu 610041, PR China.
Hong Ping
HP
Zhang
Pneumology Group, Department of Integrated Traditional Chinese and Western Medicine, State Key Laboratory of Biotherapy of China, West China Hospital, Sichuan University, Chengdu 610041, PR China.
Xin
X
Zhang
Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu 610041, PR China.
Zong An
ZA
Liang
Department of Respiratory and Critical Care Medicine, West China Hospital, Sichuan University, Chengdu 610041, PR China.
Yu Lin
YL
Ji
Pneumology Group, Department of Integrated Traditional Chinese and Western Medicine, State Key Laboratory of Biotherapy of China, West China Hospital, Sichuan University, Chengdu 610041, PR China. wcums-respiration@hotmail.com.
Gang
G
Wang
Folic acid; asthma; meta-analysis; review, systematic; risk