Vitamin Basics Selenium

Selenium (Se)Food:µg/100gTuna prepared108Brown rice boiled9Beef steak prepared14Brazil nuts1917Tilapia prepared54Cheese 45 12Red lentils boiled11Main functions: Plays an important role in thyroidhormone synthesis and metabolism Provides protection against oxidativedamage and infection Contributes to DNA synthesis Supports reproductive health(Dutch Food Composition Database, NEVO)For scientific sources, please contact info.nutritionscience@dsm.com.

Selenium (Se)Selenium is an essential trace mineral that the body needs to stay healthy. Itis important for reproduction, thyroid gland function, DNA production, andprotecting the body from damage caused by free radicals and infection. Therichest sources of selenium are animal derived foods such as meat, poultry,eggs, and dairy products, although some plant-based foods also containselenium. Selenium status can vary significantly due to low selenium soil andanimal feed in certain regions around the world. Furthermore, people who havea predominantly plant-based diet can be at risk of inadequate selenium intake.

FunctionsMeasurementSelenium is a trace element required for a range of cellularfunctions. It is widely used for the biosynthesis of the uniqueamino acid selenocysteine, which is a structural element ofselenoproteins. As such, selenium is involved withantioxidant effects, the immune function, thyroid hormonemetabolism, selenium homeostasis and transport, as well asskeletal and cardiac muscle metabolism.Dietary assessment methods are considered an impreciseway to measure selenium intake, largely due to theconsiderable variability in the selenium content of food.Instead, plasma or serum selenium are commonly used asstatus biomarkers. The analysis of selenium in hair andtoenails is also useful as a long-term biomarker.The European Food Safety Authority (EFSA), which providesscientific advice to assist policy makers, has confirmed thatclear health benefits have been established for the dietaryintake of selenium in contributing to: Maintenance of the normal function of the immune system Maintenance of normal hair Maintenance of normal nails Normal thyroid function Normal spermatogenesis Protection of cells from oxidative stressDietary sourcesSelenium is found naturally in a variety of foods, mostly incombination with amino acids in an organic form known as‘selenomethionine’, which is readily absorbed by the humanbody. There are also inorganic forms (selenate and selenite)that plants accumulate and convert to organic forms.The most important sources of selenium are meat, poultry,eggs, and dairy products, although some plant-based foodsalso contain selenium. In all cases, the selenium content canvary significantly. Differences in the dietary feed used toproduce livestock, as well as the available selenium contentof the soil and water where crops are grown can all have animpact. In China, for example, the selenium content of corn,rice and soy beans can range from 0.005 to 45 µg/kg. While inNew Zealand, where intakes were previously low, levels haveimproved following greater imports of high-seleniumAustralian wheat.Absorption and body storesThe selenium found in plant and animal sources isincorporated into various proteins and enzymes in the body(selenoproteins). Most selenium is stored in skeletal muscletissue, which accounts for around 28-46% of the total seleniumpool, although the thyroid holds the highest concentration.Based on available data, EFSA estimates the absorptionefficiency of selenium from the average diet to be 70%.

Physiological interactions Selenium and iodine play critical roles in thyroidhormone metabolism. One of the enzymes in thismetabolism is composed of two selenium atomsand catalyses the conversion of thyroid hormones. Complicated pregnancies are characterized byincreased oxidative stress (imbalance between freeradicals and antioxidants in the body, which can beharmful) in the placenta. Selenium and iodinepotentially work together to impact oxidative stressin the placental cells. Therefore, there may be aninteraction of selenium and iodine on placental andchild health.DeficiencyAdverse health effects are associated with seleniumdeficiency, including poorer immune function, problematicfertility/reproduction in men and women, fatigue, muscleweakness, and cognitive decline. Worldwide, 1 billion peoplehave been estimated to have low dietary selenium intake.Suboptimal selenium status was reported to be widespreadthroughout Europe, the United Kingdom and the Middle East,and these results agreed with previous reports highlightingthe problem. As animal-based foods are very rich inselenium, people who have a predominantly plant-based dietcan be at risk of inadequate selenium intake. In addition, it ispredicted that the concentration of selenium in soil willdecrease in the future as a consequence of climate change.These losses could increase the global prevalence ofselenium deficiency.Possible reduction of disease risk factorsCardiovascular diseaseSelenoproteins help prevent the oxidative modification oflipids, reducing inflammation and preventing platelets fromclustering (aggregating). Recent studies found that seleniumsupplementation could significantly decrease serum levels oftotal cholesterol and triglycerides. Furthermore, a positiveeffect on reducing oxidative stress and inflammation incoronary heart disease patients is also suggested.Thyroid diseaseEpidemiological evidence suggests a relationship betweenselenium levels and thyroid gland function in women.However, randomized, controlled trials of seleniumsupplementation in patients with thyroid disease have hadvarious results. Additional research is needed to determinewhether selenium supplements can help to prevent or treatthyroid disease.Effects on the brainLow selenium status has been associated with increased riskof cognitive decline, while selenium deficiency can causeirreversible brain injury. Evidence also suggests a correlationbetween low selenium status and the occurrence of seizures,Parkinson’s disease, poor co-ordination, and cognitive decline.In addition, selenium supplementation has been shown toreduce intractable childhood seizures in a few, small studies.CancerProspective studies have generally shown some benefit ofadequate selenium status, compared to low selenium status,on the risk of prostate, lung, colorectal, and bladder cancers.However, findings from trials have been mixed. More researchis needed to confirm the relationship between seleniumconcentrations and cancer risk in order to determine whetherselenium supplements can prevent any form of cancer.Immune systemLow selenium levels are associated with poor immunefunction. A growing body of evidence suggests that increasingselenium status will enhance the immune function, inparticular the ability to respond to viral infection. However,the mechanisms underlying these effects are not fullyunderstood and more research is needed.

Recommended Daily Intake (RDI)SafetyIn the U.S., the daily intake recommendation for adults is55 µg/day, while for women who are pregnant or breastfeedingthe values are slightly higher of 60 µg/day and 70 µg/dayrespectively. Values also vary according to age for childrenunder the age of 18 years. European health authorities haveset an adequate intake (AI) for selenium of 70 µg/day foradult men and women, while values for children range from15 µg/day to 70 µg/day, depending on age.Although selenium is essential for health, too much can leadto health problems. Early indicators of excess selenium intakeinclude a garlic odor in the breath and a metallic taste in themouth. The most common clinical signs of chronically highselenium intake (selenosis) are hair and nail loss or brittleness.Recommended daily intakes (RDI)GroupLife stageDose/day*Infants 6 months15 µg**Infants7-12 months20 µg**Children1-3 years20 µgChildren4-8 years30 µgChildren9-13 years40 µgChildren14-18 years55 µgAdults19-50 years55 µgAdults 51 years55 µgPregnancy 14 years60 µgBreastfeeding 14 years70 µg* Institute of Medicine (2001)** Adequate intake (AI)If not otherwise specified, this table presents RDIs.The U.S. Food and Nutrition Board (FNB) has establishedupper intake limits (UL) from food and supplements of400 µg/day for adult, with values reducing according to age.In Europe, EFSA has defined a safe upper intake level forselenium as 300 µg/day for adults, including pregnant andlactating women. The UL values for children range from60 µg/day (1-3 years) to 250 µg/day (15-17 years).Due to the potential for interactions, individuals on regularmedication should discuss their selenium status with theirhealthcare provider.Supplements and food fortificationSelenium is available in a multivitamin/multimineralsupplement, as well as a stand-alone option. The mostcommon forms used in supplements are selenomethionine orselenium-enriched yeast (grown in high-selenium mediums),as well as sodium selenite or sodium selenate. Each formoffers different bioavailability. For example, more than 90% ofselenomethionine is absorbed by the body, compared to around50% of selenium from selenite. This distinction is importantas it determines how much of this essential trace mineral isactually taken up to support important bodily functions.Currently, selenium fortification is limited. It is added tosome breakfast cereals, sports drinks, salt, and infant foods.

eggs, and dairy products, although some plant-based foods also contain selenium. In all cases, the selenium content can vary significantly. Differences in the dietary feed used to produce livestock, as well as the available selenium content of the soi