Periconceptional folic acid supplementation is a risk factor for childhood asthma: a case-control study

BACKGROUND: Several studies found an association between periconceptional folic acid supplementation and the risk of childhood asthma. But the epidemiologic evidence is still inconsistent and the underlying biological mechanisms remain unclear. METHODS: We conducted a hospital-based case-control study on childhood asthma with 548 cases and 816 normal controls in Shanghai, China. Mothers of the asthma children were asked about folic acid supplementation before and during pregnancy. Unconditional logistic regression models were employed to control for potential confounders. RESULTS: Periconceptional folic acid supplementation was associated with an increased risk of childhood asthma after adjusting for potential confounders (adjusted OR = 1.28 [95% CI 1.14–1.43]). Moreover, the adjusted OR varied by the timing of starting folic acid supplementation: before gestation: 1.31 [95% CI 1.01–1.70]; in the 1st month of gestation: 1.09 [95% CI 0.96–1.23]; and after the 1st month of gestation: 1.90 [95% CI 1.56–2.30]. We further found that the adjusted OR was the highest when periconceptional folic acid supplementation lasted more than 6 months (< 4 months: 1.21 [95% CI 1.07–1.37]; 4–6 months: 1.06 [95% CI 0.88–1.27]; > 6 months: 1.75 [95% CI 1.35–2.27]). CONCLUSIONS: Periconceptional folic acid supplementation was associated with an increased risk of childhood asthma in offspring. Further research on this issue is warranted.