Vitamin D status in pregnancy and cord blood is associated with symptoms of attention-deficit hyperactivity disorder at age 5 years: Results from Odense Child Cohort

Background: Vitamin D status in pregnancy may affect offspring neurodevelopment. Objective: The objective was to investigate the association between serum 25-hydroxyvitamin D in cord blood and pregnancy and symptoms of attention-deficit hyperactivity disorder in 5-year-old offspring. Method: In Odense Child Cohort, Denmark, 944 mother–child pairs had data on pregnancy or cord serum 25-hydroxyvitamin D and parent-rated attention-deficit hyperactivity disorder symptom score by Child Behavior Checklist for ages 1.5–5 years. Adjusted multiple linear regression and two-stage exposure analyses were performed for serum 25-hydroxyvitamin D associations to the attention-deficit hyperactivity disorder symptom score. Results: The mean (standard deviation) serum 25-hydroxyvitamin D in cord blood was 48.0 (21.8) nmol/L; early pregnancy was 65.5 (20.2) nmol/L and late pregnancy was 79.3 (25.7) nmol/L. The median (interquartile range) age of child at examination was 5.2 (5.1–5.4) years and median (interquartile range) attention-deficit hyperactivity disorder symptom score was 2 (0–3) points. In adjusted analyses, serum 25-hydroxyvitamin D of <25 nmol/L and <32 nmol/L in cord blood and <25 nmol/L in early pregnancy was associated with 0.9 [95% confidence interval: 0.4, 1.3], 0.5 [0.1, 0.9] and 2.1 [0.8, 3.4] points higher attention-deficit hyperactivity disorder symptom score vs reference. In the two-stage exposure analysis, attention-deficit hyperactivity disorder symptom score decreased by 0.4 points per 25 nmol/L increase in serum 25-hydroxyvitamin D. Moreover, serum 25-hydroxyvitamin D of <25 nmol/L in early pregnancy and cord was associated with a five-fold and a two-fold risk of attention-deficit hyperactivity disorder symptom score ⩾90th percentile, adjusted odds ratio [95% confidence interval] = 4.9 [1.3, 19.0] and 2.2 [1.2, 3.9]. Conclusion: In this cohort, serum 25-hydroxyvitamin D <25 nmol/L in cord blood and early pregnancy were risk factors for higher attention-deficit hyperactivity disorder symptom score in 5-year-old children, suggesting a protective effect of vitamin D on attention-deficit hyperactivity disorder traits at preschool age.