Follow-up at 6 to 8 Years
MAY, GENETIC DISORDER
The follow-up study was initiated in November 2019; we invited 817 families who remained in the original VIDI study until completion of the intervention at age 2 years of the child and had available home address info to participate. Of 546 families who participated in the follow-up study (55.3% of the original study population), 456 families completed online questionnaires regarding psychological and cognitive outcomes between September 2020 and May 2021. Personnel conducting follow-up were blinded to group membership. There was 1 participant excluded owing to diagnosis of a rare genetic disorder. The population of this long-term follow-up study consisted of 346 children whose parents completed the Child Behavior Checklist (CBCL) questionnaire (63.4% of those in the follow-up study); of the original 400-IU group, 169 children (34.6%) were included, and of the original 1200-IU group, 177 children (36.4%) were included. These children had somewhat more beneficial baseline characteristics regarding breastfeeding duration, maternal 25(OH)D level, smoking status, and parental education level compared with nonparticipants (eTable 1 in 