Strengths and Limitations
internalizing behaviors
MAY
This study has several strengths, among them the double-blind RCT setting, standardized data collection, and well-characterized study population. Outcomes were assessed using CBCL, a widely used, validated questionnaireThis study has several limitations as well. Of the original study population (987 families), 546 families (55.3%) remained in the 6 to 8–year follow-up study, and of these, 346 families (63.4%) completed the CBCL questionnaire. Baseline characteristics were somewhat more beneficial among the study population compared with those lost to follow-up, potentially limiting generalizability to a more diverse population. Furthermore, the proportion of children with maternal 25(OH)D levels less than 30 ng/mL was lower among study participants than in nonparticipants (33.0% vs 40.2%), influencing the number of children available for subgroup analyses. However, attrition rates were similar between supplementation groups, baseline characteristics for nonparticipants did not differ between groups, and inverse probability weighting estimation revealed no indication of attrition bias. Externalizing and internalizing behaviors at age 2 years did not differ between participants and nonparticipants, suggesting that study participants were representative of the 2-year assessment participants in this regard.Questionnaires were collected from September 2020 to May 2021, concurrently with the global SARS-CoV-2 pandemic. The pandemic may have directly and indirectly negatively influenced mental health in children.Since 2003, milk products and fat spreads in Finland have been fortified with vitamin D, resulting in improved population vitamin D levels.