The Bottom Line

Selenium is a critical mineral necessary for thyroid and reproductive function, with the latter especially true in males.

Although some research indicates a deficiency in selenium can cause problems in pregnancy, selenium’s role and requirement during pregnancy is unknown, and supplementation is not recommended due to a lack of evidence for any benefit (unless a woman is deficient).

It is always recommended that women talk to their health provider (HCP) before taking any supplementation during pregnancy, to include selenium.

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Background

Selenium is a mineral contained in all cells; it is critical for reproductive, thyroid and immune system function, and may even protect the fetus from environmental pollutants.

The largest concentrations of selenium in the body are found in the thyroid, sex glands, sperm cells, and skeletal muscle.

In general, selenium deficiency impairs fertility and lowers the quality and motility of sperm.

Pregnancy

The concentration of selenium in the blood of women during pregnancy varies from country to country, and researchers do not agree how pregnancy affects a woman's selenium status.  The leading hypothesis is that selenium levels gradually and progressively decrease throughout pregnancy (but others have noticed no change).

Selenium does, however, progressively accumulate in the organs of the growing fetus, and at the end of pregnancy, mostly gets stored in the fetus’ liver. Higher concentrations of selenium are found in umbilical cord blood than in the mother’s blood.

Although not much is known about selenium during pregnancy, a study published in June 2021 found that higher levels of selenium or manganese in the mothers’ blood were associated with lower blood pressure readings in their children at clinic visits 3 to 15 years later, likely due to their antioxidant properties.

Deficiency

Due to selenium’s effects on the reproductive system, immune system, and thyroid, it is possible a lack of selenium could increase the risk of pregnancy complications such as miscarriage, low birth weight, preeclampsia, and damage to the nervous and immune systems of the fetus, although these effects are debated.

A lack of selenium may also impair the body's ability to activate thyroid hormones, which are critical during pregnancy.

It is also theorized that women who are deficient in selenium can be more affected by physiological stressors which could then predispose them to certain illnesses/infections, which could then lead to pregnancy complications.

Supplementation

Regardless of the above, there is not enough consistent evidence for routine selenium supplementation during pregnancy. Further, it is likely pregnant women obtain enough selenium in their diet.

Dietary intake of selenium throughout the world ranges greatly, from 30 to 50 micrograms (mcg) in most European countries to more than 100 mcg in the United States, Canada and Japan, well above the recommended 60 mcg/day.

Note: Selenium is generally not included in prenatal supplements in the United States, or standard women’s multivitamins.  It is more commonly found in men’s multi-vitamins.

The tolerable upper intake level for selenium in adults is 400 mcg/day, based on the prevention of early signs of selenium toxicity.

These symptoms can include: a garlic odor in the breath, a metallic taste in the mouth, hair and nail loss or brittleness, lesions of the skin and nervous system, nausea, diarrhea, skin rashes, spotted teeth, fatigue, irritability, and nervous system problems.

Acute and fatal toxicities have occurred with ingestion of gram quantities of selenium (1,000,000 mcg are in 1 gram).

Food Sources

Brazil nuts contain very high amounts of selenium (68 to 91 mcg per nut) and could cause selenium toxicity if consumed regularly.

Other rich sources of selenium include fish, shrimp, turkey, chicken, oatmeal, organ meats, cereals, grains, dairy products, eggs, and bread.

The amount of selenium in a plant food depends on the amount of selenium in the soil; therefore, selenium content in certain foods varies by geographic location.

Action

Pregnant women should discuss any concerns they have regarding their selelnium status with their HCP.

Women should also consider having a discussion with their provider regarding their overall nutrition, as well as an assessment of their current diet. HCPs are trained to look for areas in which women may be able to improve their nutrition during pregnancy based on vitamins/minerals they may be lacking.

Resources

Selenium Fact Sheet (U.S. National Institutes of Health, Office of Dietary Supplements)

References

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