Selenium is a biologically active non-metal that serves important antioxidant functions and is crucial for various biological processes including protein synthesis and reproduction. Deficiency in selenium can lead to diseases such as Keshan disease and Kashin-Beck disease, while excessive intake may result in selenosis with symptoms like garlic breath odor and hair loss. Daily dietary requirements vary by age, with sources including dairy, vegetables, and cereals, and selenium's body concentration is highest in the liver, kidney, and nails.

2. Selenium
• Essential element
• Chemistry :
– Non-metal
– Biologically active compounds contain Secys.
• Se is substituted for S in Cys
• UGA – co-translational insertion
– SeMet. – only in plants
• Identical to Met

3. Selenium
• Powerful antioxidant, works closely with
Vitamin E to protect body from
oxidation.
• Total body content of selenium is about
4 to 10mg.
• Highest concentration – liver, kidney &
finger nails.

4. • Non-specifically incorporated into protein
pool
• Is present in major proteins – albumin &
Hb
• Selenium in SeMet constitutes ½ the total
dietary intake
• Contributes to Secys. synthesis

5. Sources
Dairy products, vegetables, fruits,
Cereals (good sources)
Daily Requirement:
Adults: 50 - 100µg/day
Children: 20 - 120µg/day
Infants get their selenium through breast milk.
Se intake depends on the nature of the soil in which
food crops are grown.
Se is a well-known growth stimulant in agriculture.

6. Absorption, Metabolism & Excretion

7. • Se is absorbed from the duodenum & transported
bound to β-lipoproteins in the form of seleno
methionine.
• Body Se – 15 mg
Normal serum level is 50 - 100µg/dl.
• 50% -60% of plasma selenium is present as
selenoprotein P
--Transport protein for se
– Basic protein--Multiple His residues
– 10atoms Se/molecule
• 30% is present in GSH Px
• Remainder in albumin as SeMet
Absorption, Metabolism & Excretion(contd)

8. • Powerful antioxidant, works closely with Vitamin E to
protect body from oxidation.
• Highest concentration – liver, kidney & finger nails.
• Excretion :
– Urinary output
– Depends on intake
Absorption, Metabolism & Excretion(contd)

9. Selenophosphate synthetase:
– Required for intracellular synthesis of
selenoproteins

11. Functions
• 30 biologically active Secys- proteins
• 15 –purified & functions identified
• Important Se proteins & their functions :
1. GSH Px:
• 4 isoforms
• 1- RBC
• 2-GIT
• 3- plasma
• 4- cell membranes

13. 2. Iodothyronine De-iodinase:
Converts T4 to its active form T3
• Type I – liver , kidney & muscle
• 90% of plasma T3
• Type II & III – pituitary , brain & brown
adipose tissue

14. 3. Thioredoxin reductase :
– maintains intracellular redox state
– Catalyses NADPH dep. Reduction of
thioredoxin
– 2 isoforms

16. 5. Reproduction :
– Concentration in testis is highest in in adult
tissue
• Required for normal development of spermatozoa
• Present in mid-piece as a selenoprotein in
mitochondria
– Necessary for testosterone synthesis
– Maintains sperm viability

17. 6. Non-specific antioxidant :
– Availability of vit.E  Se requirement
7. Role in cancer chemoprevention

18. Deficiency
• Deficiency in selenoprotein production esp. GSH Px – signs
and symptoms of se. deficiency disease
1. KESHAN DISEASE:Endemic cardiomyopathy
-Reported from Keshan province in china, where soil is
deficient in selenium.
-This disease is characterised by multifocal myocardial
necrosis, reduced serum selenium level, cardiac
arrythmias & cardiac enlargement.
2.KASHIN- BECK DISEASE:
– Severe degenerative osteo arthrosis
– particularly affecting children between 5 to 13 yrs
age.

19. Kashin- beck disease:

20. • 3. Nutritional deficiency in hospital
patients:
– Muscle weakness
– Cardiomyopathy
– Pseudoalbinism

21. • Other deficiency effects
– Thyroid function
– Reproductive disorders
– Mood disorders
– Immune functions
– Infections cause deficiency

22. Toxicity
• Selenosis
• Toxic dose is 900µg/day.
• China & US – soil has excess Se and hence
foods contain more Se
• Signs :
– Garlic odor in breath( due to the presence of
dimethyl selenide in expired air).
– Hair loss
– Nail damage
• Metal polishes & anti-rust compounds