A recent review article presents the evidence that low selenium status in pregnant women may be implicated in the following complications [Duntas 2020]:
- miscarriage
- preeclampsia
- pre-term birth
- retarded fetus intrauterine growth
- post-partum hypothyroidism and auto-immune thyroiditis
To ensure an optimal pregnancy outcome, Dr. Leonidas Duntas recommends that physicians take an individualized approach and prescribe dietary and supplemental selenium intakes that are tailored to the pregnant woman’s needs.
Why is Adequate Selenium Important for Pregnant Women?
Selenium is an essential trace element. Its intake and status in the blood plasma can vary considerably according to a number of factors [Duntas 2020]:
- differences in diet and nutrition
- differences in soil and plant selenium content
- ethnic differences
- genetic differences
Without a blood selenium test, it is not possible to know whether women planning a pregnancy have sufficient circulating selenium. The Mayo Clinic reports that the normal selenium concentration in adult human blood serum in the United States is 70 to 150 micrograms per liter with a population mean value of 98 micrograms per liter.
In much of Europe, especially northern Europe, and the Middle East, serum selenium concentrations could be notably lower [Stoffaneller & Morse 2015].
The Biological Functions of Selenium
In human cells, selenium does not normally exist in its elemental form. Its primary biological functions are performed when the selenium is incorporated into the 21st amino acid selenocysteine, which then becomes a component of selenoproteins. These selenoproteins play a major role in antioxidant defense mechanisms, in redox regulation, and in thyroid hormone metabolism [Duntas 2020].
Dr. Duntas lists the most important selenoproteins:
- the deiodinases
- the glutathione peroxidases
- the thioredoxin reductases
- the selenocysteine insertion binding protein 2 (SECISBP2)
- the selenium transport protein (SELENOP)
Selenium deficiency has been associated with autoimmune thyroid diseases.
- The deiodinases control thyroid hormone turnover. They regulate the conversion of thyroxine (T4) to triiodothyronine (T3) [Duntas 2020].
- The glutathione peroxidases and the thioredoxin reductases are involved in thyroid gland protection by their modulation of redox activities [Duntas 2020].
Selenium and At-Risk Pregnancies
Current evidence indicates that selenium deficiency during pregnancy is associated with a number of adverse effects on the fetus and the mother as well as with increased biomarkers of oxidative stress. There is now evidence that selenium supplementation may reduce the incidence of the adverse events and may decrease the risk of autoimmune thyroiditis complications and may prevent post-partum hypothyroidism. However, there is still a need to establish appropriate dosages and durations for the selenium supplementation [Duntas 2020].
Selenium and Miscarriage
Dr. Duntas reviews the evidence establishing a correlation between low selenium intakes/status and the risk of miscarriage. Although a causal relationship has not been conclusively demonstrated, he recommends that physicians consider selenium supplementation on an individual basis during the first trimester, especially for women who live in selenium-poor regions and for women known to be at risk for miscarriage [Duntas 2020].
Selenium and Pre-eclampsia
A 2015 meta-analysis of 13 observational studies with 1515 participants and 3 randomized controlled trials with 439 participants has shown [Xu 2015]:
-There is an inverse relationship between blood selenium levels and the risk of pre-eclampsia.
–Supplementation with selenium significantly reduces the incidence of pre-eclampsia.
The important thing is to determine the dose, the beginning time, and the duration of selenium supplementation of pregnant women at risk for pre-eclampsia [Xu 2015].
Selenium and Pre-Term Births
Dr. Duntas reviews the evidence for an association between low maternal selenium intakes/status and the risk of pre-term birth. Low maternal serum selenium concentrations in early pregnancy should be considered a marker for the increased risk of small-for-gestational-age newborns [Duntas 2020].
Selenium and Autoimmune Thyroiditis During or After Pregnancy
Dr. Duntas points out that the current guidelines for autoimmune thyroiditis do not recommend selenium administration during pregnancy; even so, Dr. Duntas suggests that autoimmune thyroiditis patients who are at high risk and who have low selenium levels (defined as below 80 micrograms per liter) in early pregnancy, be considered for Se supplementation [Duntas 2020].
Bottom Line: Selenium and Pregnancy
Dr. Duntas reviews a number of studies that give evidence for the importance of adequate selenium levels during pregnancy and comes to the following conclusions [Duntas 2020]:
- Selenium deficiency is implicated in miscarriage, preeclampsia, retarded fetus intrauterine growth, and preterm birth.
- Pregnant women with autoimmune thyroiditis in conjunction with low selenium levels are at an increased risk of an adverse pregnancy outcome and an increased risk of postpartum hypothyroidism.
- Selenium supplementation of low-selenium status pregnant women should be considered on an individual basis.
- Selenium status below 80 micrograms per liter seems to call for selenium supplementation.
- Selenium status above 120 micrograms per liter seems to signal that there is no need for supplementation.
Sources
Duntas, L.H. Selenium and at-risk pregnancy: challenges and controversies. Thyroid Res 13, 16 (2020).
Stoffaneller R, Morse NL. A review of dietary selenium intake and selenium status in Europe and the Middle East. Nutrients. 2015 Feb 27;7(3):1494-537.
Xu M, Guo D, Gu H, Zhang L, Lv S. Selenium and Pre-eclampsia: a Systematic Review and Meta-analysis. Biol Trace Elem Res. 2016 Jun;171(2):283-292.
The information presented in this review article is not intended as medical advice and should not be used as such.
15 December 2020