Deficiency of selenium, an essential trace element, has been implicated in adverse birth outcomes and the growth of infants and young children. We used data from a randomized controlled trial to examine associations between selenium biomarkers in whole blood (WBSe), serum and selenoprotein P (SEPP1) in maternal delivery and venous cord (VC) blood, and birth weight, and adverse birth outcomes. Furthermore, we examined associations between selenium biomarkers and infant growth outcomes (age adjusted length, weight, head circumference and weight-for-length z-scores) at birth, one, and two years of age using linear regression. WB and serum selenium in delivery and VC specimens were negatively associated with birth weight (adjusted beta, 95% CI: WBSe delivery: -26.6 (-44.3, -8.9); WBSe VC: -19.6 (-33.0, -6.1)); however, delivery SEPP1 levels (adjusted beta;: -37.5 (-73.0, -2.0)) and VC blood (adjusted beta, 82.3 (30.0, 134.7)) showed inconsistent associations across biomarkers. We found small to moderate associations between infant growth and WBSe VC (LAZ beta, 95% CI, at birth: -0.05 (-0.1, -0.01)); 12-months (beta, -0.05 (-0.08, -0.007)). WAZ also showed weak negative associations with delivery WBSe (at birth: -0.07 (-0.1, -0.02); 12-months: -0.05 (-0.1, -0.005)) and in WBSe VC (beta; at birth: -0.05 (-0.08, -0.02); 12-months: -0.05 (-0.09, -0.004)). Mechanisms connected to redox biology and its antioxidant effects have been causally associated with the protective properties of selenium. Given the fine balance between nutritional and toxic properties of selenium, it is possible that WB and serum selenium may negatively impact growth outcomes, both in utero and postpartum.

The authors have declared no competing interest.

This secondary data analysis was funded through the Microbiome, Infections, Child Growth and Development Fellowship, Centre for Global Child Health, Hospital for Sick Children, Toronto, Canada. The parent MDIG study and selenium biomarker analyses were funded through grants from the Bill & Melinda Gates Foundation.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The parent study (MDIG: 1000057297) was conducted according to the guidelines laid down in the Declaration of Helsinki and all procedures involving human subjects and secondary specimen use sub-studies including the heavy metals protocol were approved by ethical review committees at the Hospital for Sick Children (Canada) and the International Center for Diarrheal Disease Research, Bangladesh. All women in the study provided written informed consent which included the use of biological specimens for future research purposes. This sub-study was approved by the ethics review board at the Hospital for Sick Children. The MDIG Trials was registered with clinicaltrials.org, with trial registration number: NCT01924013 (https://www.clinicaltrials.gov/ct2/show/NCT01924013).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors