Researchers from the University of Colorado and the USDA Agricultural Research Service studied women in Guatemala, India and Pakistan and found that maternal selenium supplementation did not impact serum concentrations.
“[It suggests] that supplementation may not overcome the impact of low intake and the high demands of pregnancy and early lactation,” the researchers wrote. “Larger studies in high-risk regions are needed to further clarify the relationship between maternal selenium deficiency and infant outcomes.”
The study was funded by the Bill & Melinda Gates Foundation, the Eunice Kennedy Shriver National Institute of Child Health and Human Development and Office of Dietary Supplements.
Selenium’s importance in pregnancy
Selenium, a trace element, holds key roles in the body that may affect fetal health. Selenium is critical for thyroid hormone function and acts to neutralize oxidative stress.
“A possible mechanism for selenium’s impact on fetal growth is through its role in thyroid hormone function,” the researchers explained. “Thyroid hormones are essential regulators of intrauterine growth and brain development, with the embryo completely reliant on normal maternal thyroid function in the first trimester.”
Additionally important is the amount of selenium in the soil that varies depending on location, having an impact on community selenium status. Soil selenium is predicted to decline because of climate change, putting greater stress on populations at risk of selenium deficiency.
During pregnancy, selenium deficiency is connected to gestational diabetes, pre-eclampsia, gestational hypertension and low birth rate while increased dietary selenium is linked to a decrease in preterm birth and higher birth weight.
Human milk selenium concentrations are connected to maternal selenium status as well, underscoring the importance of selenium sufficiency to ensure adequate consumption for breastfed infants.
Selenium is also being studied for its possible connection to improving linear growth and neurodevelopmental outcomes in the first two years of life.
“Despite its importance in pregnancy and public health, there is insufficient evidence to date to guide appropriate intake during pregnancy to potentially reduce adverse outcomes and prevent deficiency across populations globally,” the researchers noted.
Study details
The investigation was a secondary analysis of the Women First Trial, a randomized controlled study exploring the impact of small-quantity lipid-based nutrition supplement (sqLNS) containing 130 mg of selenium on fetal growth.
sqLNS administration began around 12 weeks of gestation in the women in the three populations studied. The researchers measured maternal serum selenium at 12 and 34 weeks of gestation and at three months postpartum.
“We found no significant associations between maternal selenium at 12 and 34 weeks with birth weight- length-, or head circumference-for-age z-scores,” the researchers explained. “There were also no associations with low birth weight, small for gestational age or prematurity.”
The study found that mean selenium concentrations decreased throughout the pregnancy and dropped to their lowest three months postpartum. Women in Pakistan had the lowest selenium levels, and in all countries where women were studied, the researchers found maternal selenium supplementation did not affect serum concentrations.
Study participants in Pakistan who took sqLNS with 130 mg of selenium were administered twice the recommended daily allowance for pregnancy but still failed to “increase maternal serum selenium or prevent development of deficiency during pregnancy and at three months postpartum,” the researchers noted.
Additionally, the researchers used inorganic selenium selenite that has lower bioavailability compared with organic selenium. They explained that organic selenium may be more likely to raise maternal serum concentrations and should be considered to use in future study of populations at high risk of selenium deficiency.
Source: The Journal of Nutrition. doi: 10.1016/j.tjnut.2025.101279. “A Multicountry Analysis of Maternal Selenium Status in Pregnancy and Lactation and Infant Birth Outcomes: Findings from the Women First Maternal Preconception Study.” Authors: Stephanie P. Gilley et al.
