Maternal Folate Intake during Pregnancy and Childhood Asthma in a Population-based Cohort.

Rationale: A potential adverse effect of high folate intake during pregnancy on children's asthma development remains controversial. Objectives: To prospectively investigate folate intake from both food and supplements during pregnancy and asthma at age 7 years when the diagnosis is more reliable than at preschool age. Methods: This study included eligible children born 2002-2006 from the Norwegian Mother and Child Cohort Study, a population based pregnancy cohort, linked to the Norwegian Prescription Database. Current asthma at age 7 was defined by asthma medications dispensed at least twice in the year (1,901 cases; n = 39,846) or by maternal questionnaire report (1,624 cases; n = 28,872). Maternal folate intake was assessed with a food frequency questionnaire validated against plasma folate. We used log-binomial and multinomial regression to calculate adjusted relative risks with 95% confidence intervals. Measurements and Main Results: Risk of asthma was increased in the highest versus lowest quintile of total folate intake with an adjusted relative risk of 1.23 (95% confidence interval, 1.06-1.44) that was similar for maternally reported asthma. Mothers in the highest quintile had a relatively high intake of food folate (median, 308; interquartile range, 241-366 mu g/d) and nearly, all took at least 400 mu g/d of supplemental folic acid (median, 500; interquartile range, 400-600 mu g/d). Conclusions: In this large prospective population-based cohort with essentially complete follow-up, pregnant women taking supplemental folic acid at or above the recommended dose, combined with a diet rich in folate, reach a total folate intake level associated with a slightly increased risk of asthma in children.