This document discusses trace elements and minerals that are essential for human beings, focusing on iron. It provides details on: 1. Iron is an essential trace element required in small amounts. It is important for transporting oxygen via hemoglobin and myoglobin and is involved in oxidative reactions and tissue respiration as part of enzymes. 2. Iron is absorbed in the small intestine and transported via transferrin in plasma. It is stored in liver, spleen and bone marrow bound to protein ferritin or hemosiderin. Iron balance is maintained through intestinal absorption to replace losses. 3. Iron deficiency is common worldwide and can result from inadequate dietary intake or malabsorption. Good dietary sources include meat, fish,

1. Minerals
Trace Elements
R. C. Gupta
M.D. (Biochemistry)
Jaipur (Rajasthan), India

2. Some minerals essential for human beings
are required in minute quantities
These are known as trace elements
These are also known as micro-nutrients

3. The trace elements includeː
1. Iron
2. Iodine
3. Copper
4. Zinc
5. Cobalt
6. Manganese
7. Molybdenum
8. Chromium
9. Selenium
10. Fluorine

4. Iron
Total amount of iron in an adult human
being is 3.5-4.5 gm
Blood and blood-forming organs are the
largest reservoirs of iron
But small amounts of iron are present in
nearly every tissue

5. Important iron-containing
compounds are:
• Haemoglobin
• Myoglobin
• Ferritin
• Haemosiderin
• Transferrin
• Cytochromes
• Iron-containing enzymes

6. About 70% of the body iron is present in
haemoglobin and 5% in myoglobin
Ferritin and haemosiderin, which are storage
forms of iron, contain about 20% of the body iron
Transferrin, an iron carrier protein present in
plasma, contains 0.1% of the body iron
The remaining iron is present in cytochromes and
enzymes

7. Haem
Haemoglobin
Each subunit contains one iron atom
Haemoglobin is a tetramer made up of
four subunits

8. Myoglobin
Haem
Myoglobin is present in muscles
It is a monomer having one iron atom

9. Cytochromes
Cytochromes are present in respiratory
chain, and support tissue respiration
Cytochrome P-450 and cytochrome b5
are components of microsomal hydroxy-
lase system

10. Ferritin
Ferritin is one of the storage forms of iron
The protein portion of ferritin is known as
apoferritin
Apoferritin combines with iron to form
ferritin

11. Ferritin is present in:
• Liver
• Spleen
• Bone marrow
• Brain
• Kidneys
• Intestine
• Placenta

12. The first step in the synthesis of ferritin is
formation of apoferritin
Synthesis of apoferritin is induced by the
entry of ferrous iron in the cell
This is followed by oxidation of ferrous
iron to the ferric form
Ferric iron forms ferric hydrophosphate
micelles

13. Apo-ferritin Ferritin
80 Å
Ferric hydro-
phosphate micelles
Ferric hydrophosphate micelles enter
the protein shell to form ferritin
120 Å

14. Apoferritin is made up of 24 subunits of
two types – H and L
Molecular weight of H subunits is 21,000
and that of L subunits is 19,000
The proportion of H and L subunits in
apoferritin differs in different tissues
The subunits are joined together to form
a hollow sphere

15. Apoferritin
L Subunits
H Subunits

16. Ferric hydrophosphate micelles are
present in the hollow space in ferritin
When fully saturated, a molecule of
ferritinː
Contains 4,500 atoms of iron
Has a molecular weight of 900,000

17. Iron stored
inside ferritin

18. Haemosiderin is a granular iron-rich
protein
Unlike ferritin, it is insoluble in water
The exact structure of haemosiderin is
not known
Haemosiderin

19. Iron is first stored in the body in the form of
ferritin
As the iron stores increase, older ferritin
molecules aggregate to form haemosiderin
Some of the protein is degraded in this
process
Therefore, percentage of iron in haemo-
siderin is higher than in ferritin

20. Normally, two-thirds of stored iron is in
the form of ferritin
The remaining one-third is stored in the
form of haemosiderin

21. Transferrin is a carrier protein which
transports iron in circulation
Free iron is toxic, and has a tendency to
precipitate
These problems are overcome by
combining iron with transferrin
Transferrin

22. Transferrin is a glycoprotein with a
molecular weight of about 80,000
It is made up of a single polypeptide
chain
One molecule of transferrin can transport
up to two ferric atoms

23. Transferrin
(By Emw - Own work, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=9444665)

24. Transferrin present in plasma may be:
Diferric transferrin (carrying two
ferric ions)
Monoferric transferrin (carrying
one ferric ion)
Apotransferrin (carrying no ferric
ions)

25. Transferrin carries iron to and from
various tissues through circulation
There are specific receptors for trans-
ferrin on the cell membrane
The receptors are transferrin receptor 1
(TfR1) and transferrin receptor 2 (TfR2)

26. TfR1 is synthesised by all iron-
requiring cells
It is present in high numbers on:
Immature erythroid cells
Rapidly dividing cells
Placental cells

27. TfR2 is synthesised by:
Liver cells
Haematopoietic cells
Duodenal crypt cells

28. TfR is a transmembrane glycoprotein made
up of two polypeptide chains
The polypeptide chains are joined by two
disulphide bonds
Each polypeptide possesses one binding
site for transferrin
TfR has greater affinity for diferric transferrin
than for monoferric or iron-free transferrin

29. Transferrin
Transferrin
receptor
Iron
Cell
membrane

30. Binding of iron-carrying transferrin to its
receptor results in endocytosis of both,
forming an endosome
Proton pumping into endosome changes
the conformation of transferrin and its
receptor

31. The conformational change results in
release of iron
Fe3+ is reduced to Fe2+ by ferrireductase
Iron is transported across the membrane
of endosome into the cytoplasm

32. Transferrin receptor and apotransferrin
are returned to the cell surface
Apotransferrin is released in plasma to be
charged with iron again
Transferrin, once formed, can participate
in 100-200 cycles of iron transport

33. Normal concentration of transferrin in
plasma is 200-400 mg/dl
This amount of transferrin is capable of
carrying 250-400 mg of iron/ dl of plasma
This is known as the total iron binding
capacity of plasma

34. Normal plasma iron level is 50-175 µg/dl
This means that the iron binding capacity
of plasma is nearly 30% saturated in
healthy subjects

35. Several enzymes require iron for their
catalytic activity
In some cases, iron forms an integral part
of the enzyme molecule
In others, presence of iron is required for
the catalytic activity of the enzymes
Iron-containing enzymes

36. The iron-containing enzymes are mostly
concerned with biological oxidation
Examples of such enzymes are catalase,
peroxidase, aconitase, xanthine oxidase,
succinate dehydrogenase etc

37. Iron is a transition metal, and can exist in
two redox states: Fe2+ and Fe3+
At the oxygen concentrations prevailing in
the body, the stable state of iron is Fe3+
But reduction of Fe3+ to Fe2+ is important
because most of the functions of iron
depend upon the ferrous form
Functions of iron

38. Moreover, Fe2+ is the only form that can
be transported across membranes
Fortunately, the two forms are readily
inter-convertible

39. Functions
Transport of oxygen
Oxidative reactions
Tissue respiration

40. The most important function of iron is to
transport oxygen in the body
This function is performed by haemo-
globin
A similar function is performed in muscles
by myoglobin
Transport of oxygen

41. Iron is a component of various oxido-
reductase enzymes
As such, it plays a role in a number of
oxidative reactions
Oxidative reactions

42. As a component of cytochromes in the
electron transport chain, iron is involved
in tissue respiration
It is the iron component of cytochromes
that accepts and donates electrons
Tissue respiration

43. Iron status depends upon the relative rates
of iron absorption and iron excretion
Iron absorption is the major mechanism for
maintaining normal iron balance
Iron balance

44. Iron metabolism is said to occur within a closed
system in the body
There is hardly any exchange of iron between
man and his environment
The iron present in the body is continuously
reutilized
Only a minute amount of iron is lost everyday
from the body in the form of exfoliated cells

45. The faecal iron loss in 0.4-0.5 mg a day
The urinary iron loss is about 0.1 mg a day
About 0.2-0.3 mg of iron is lost daily from the skin
along with the exfoliated cells
Thus, the total iron loss is just under one mg a
day

46. In premenopausal women, there are two
additional routes of iron loss
About 20-25 mg of iron is lost with
menstrual blood in each cycle
This is equivalent to a daily loss of 0.7-0.8
mg of iron

48. Iron balance is maintained by intestinal
absorption of iron
Iron lost is replenished by intestinal iron
absorption

49. Intestinal absorption of iron is affected
by:
• Body iron stores
• Erythropoietic activity
• Degree of saturation of plasma
transferrin
• The amount of dietary iron
• Valency of ingested iron (Fe+2 or Fe+3)
• Presence of other substances in the
food

50. More iron is absorbed when:
• Body iron stores are low
• Erythropoietic activity is high
• Saturation of plasma transferrin is low
• Iron is ingested in ferrous form

51. Presence of the following in food
increases iron absorption:
• Ascorbic acid
• Succinic acid
• Histidine
• Cysteine
Presence of the following in food
decreases iron absorption:
• Phytates
• Phosphates

52. Iron can be absorbed from all segments
of the small intestine
But presence and normal functioning of
stomach are essential
Achlorhydric and gastrectomized persons
absorb less iron as compared to normal
persons

53. Gastric enzymes and
hydrochloric acid:
Release iron from iron-
containing foods
Reduce ferric iron to
the ferrous form

54. Enterocytes (mucosal cells of
intestine) possess channels for:
Entry of iron on the luminal side
Exit of iron on the basolateral side

55. Iron is present in food as either inorganic
iron or haem iron
Inorganic iron is about 90% of the total
and haem contains the remaining 10%

56. Bioavailability of haem iron is very high; its
absorption is not hampered by other food
constituents
Intact haem moiety is absorbed by entero-
cytes via haem-carrier protein 1 (HCP1)
In the cells, iron is released from the proto-
porphyrin ring by haem oxygenase-1

57. Inorganic iron is present in the diet mostly
in ferric form
It is reduced to ferrous form by duodenal
cytocrome B (DcytB)
DcytB is present on the brush border
epithelium
Ascorbate may be an electron donor for
this reaction

58. Ferrous ions are transported into cells via
divalent metal transporter 1 (DMT1)
DMT1 is present on luminal membrane of
duodenal enterocytes
DMT1 is not a specific iron transporter
It also mediates transport of other divalent
metal cations such as Zn+2, Mn+2 and Cu+2

59. DMT1 is also present on the membrane of
endosomes
It mediates iron transport from endosomes
into the cytoplasm of the cell

60. The iron absorbed by the enterocyte, can
be stored within the cell as ferritin
Or it can be transported into circulation
across the basolateral membrane
Iron is transported across the basolateral
membrane via a specific transporter,
ferroportin

61. Transport across basolateral membrane
requires a change in redox state of iron
The intracellular Fe2+ form has to change
into extracellular Fe3+ form
This conversion is brought about by
hephaestin, a ferroxidase

62. All the iron that enters circulation is bound
to transferrin
Affinity of transferrin for iron at normal pH
of blood is extremely high
Transferrin delivers iron to the cells that
need it
The main iron consumers are red cell
precursors

63. Iron homeostasis is maintained by regulating
its absorption
It is believed that ferritin content of entero-
cytes determines the absorption of iron
These cells are formed in the crypts of
Leiberkuhn
Regulation of iron absorption

64. Goblet cells
Enterocytes
Crypt of
Leiberkuhn
Villus
Tip of villus

65. The enterocytes reach the tip of the villi
and are shed off into the intestinal lumen
Their average life-span is three days
The function of ferritin in these cells is to
block the absorption of iron

66. The enterocytes formed during a period of
iron sufficiency are rich in ferritin
These cells will absorb very little iron during
their life-span
Moreover, when these are shed off, their
iron content will also be lost in faeces

67. Conversely, the cells formed during a
period of iron deficiency are poor in ferritin
These cells absorb more iron and transfer it
into the plasma

68. Homeostatic mechanisms ensure that:
Systemic iron stores in the body are
adequate
Each cell has an adequate amount
of iron

69. The main sources of iron for cells are:
Iron absorbed by enterocytes
Iron stored in liver cells
Iron present in reticuloendothelial
macrophages

70. Enterocytes, liver cells and macrophages
release iron through ferroportin
Ferroportin is the sole iron export channel
Iron export requires a change in the redox
state of iron by ferroxidase
The ferroxidase is hephaestin in the
duodenum and ceruloplasmin elsewhere

72. Macrophages are an important source of
iron for erythropoiesis
The macrophages obtain iron from aged
erythrocytes
Aged erythrocytes are engulfed by macro-
phages in the reticulo-endothelial system
Their haemoglobin is broken up into haem
and globin

73. The iron present in haem is released by
haem oxygenase-1
It is either stored within the macrophages
or is released into circulation
The iron released into plasma is taken up
by transferrin

74. Most of the iron used for erythropoiesis
comes from haemoglobin recycling
The amount of iron recycled every day is
10-20 times the amount absorbed by the
intestine

75. Hepcidin is a peptide hormone synthesised
in liver
Action of hepcidin is targeted at ferroportin
Hepcidin is a negative regulator of ferro-
portin
Besides being an iron export channel,
ferroportin also acts as hepcidin receptor
Role of hepcidin in iron homeostasis

76. Hepcidin binding to ferroportin causes its
internalisation and lysosomal degradation
Loss of ferroportin decreases iron efflux
from the cell
This leads to intracellular iron retention
As a result, plasma iron is decreased

77. Requirement
Only a small proportion of the dietary iron
is normally absorbed
Hence, much larger amounts have to be
provided in diet than the requirement

78. Age and sex Requirement
Infants 6-10 mg/day
Children 10 mg/day
Adolescents 12 mg/day
Adult men and postmenopausal
women 10 mg/day
Premenopausal and lactating
women 15 mg/day
Pregnant women 30 mg/day
EMB-RCG

79. Iron is present in animal as well as plant
foods
Iron absorption from animal foods much
more efficient than that from plant foods
On a mixed diet, healthy subjects
absorb 5-10% of the dietary iron
Dietary sources

80. Animal sources of iron
EggsFishMeat
Liver Kidney Heart

81. Plant sources of iron
Whole wheat Figs Dates
Beans SpinachNuts

82. Iron deficiency is widespread both in poor
and in affluent countries
Iron deficiency is the commonest cause
of anaemia throughout the world
Iron deficiency

83. Iron deficiency can result from:
Inadequate intake
Malabsorption
Blood loss

84. Inadequate intake is likely when the
requirement is high e.g. in:
Infancy
Adolescence
Pregnancy

85. Malabsorption can be due to:
Steatorrhoea
Coeliac disease
Gastrectomy

86. Persistent blood loss can occur from:
Genital tract
Gastrointestinal tract
Hookworm infestation

87. The earliest change in iron deficiency is a
depletion of body iron stores
Other changes follow progressively
Plasma transferrin saturation is decreased
Plasma iron is decreased

88. Microcytic hypochromic anaemia develops
Hemoglobin level falls
Poikilocytosis becomes evident

90. Severe and prolonged
deficiency leads to:
Koilonychia
Angular stomatitis
Glossitis
Pharyngeal and oesophageal webs
Atrophic gastritis
Partial villus atrophy

91. Iron overload
Iron overload is much less common than
iron deficiency
Two types of iron overload syndromes are
known:
Haemosiderosis
Haemochromatosis

92. The excess iron is deposited in reticulo-
endothelial cells
There is no tissue damage
Excess iron enters via parenteral route
This can be due to repeated blood
transfusions e.g. in thalassaemia
Haemosiderosis

93. Haemochromatosis
Haemochromatosis can be primary or
secondary
Primary haemochromatosis is genetic
The genes implicated in primary
haemochromatosis are:
Hepcidin
gene
Ferroportin
gene
TfR2
gene

94. The genetic defect leads to excessive
intestinal absorption of iron
Excess iron is deposited in liver, heart,
skin, pancreas and other endocrine glands
The condition is also known as bronze
diabetes

95. The clinical abnormalities in
haemochromatosis are:
• Hepatomegaly
• Cardiomegaly
• Congestive heart failure
• Hypogonadism
• Diabetes mellitus
• Bronze-coloured pigmentation of
skin

96. Serum iron, ferritin and saturation of iron-
binding capacity are increased in haemo-
chromatosis
Phlebotomy and iron-chelating agents
e.g. desferrioxamine are used to remove
excess iron

97. Secondary haemochromatosis may occur in
alcoholic liver disease
Iron deposition is usually confined to hepatic
tissue
South African Bantus are known to develop
haemochromatosis
It is due to heavy intake of iron present in an
alcoholic beverage brewed in iron vessels

98. Total iodine in an adult is 45-50 mg
About 10-15 mg is present in the thyroid
gland
Muscles contain about 25 mg
About 5 mg is present in skin, 3 mg in the
skeleton and 2 mg in liver
Iodine

99. The only known function of iodine is in the
synthesis of thyroid hormones
The thyroid gland synthesizes tri-iodo-
thyronine (T3) and tetra-iodothyronine (T4)
These two are synthesized from iodine
and tyrosine residues of thyroglobulin
Functions

100. The thyroid gland:
Actively takes up iodide ions
from plasma
Oxidizes iodide to iodine
Incorporates iodine into tyrosine
residues of thyroglobulin

102. Two DIT residues combine with each
other to form thyroxine (T4)
One MIT and one DIT residues combine to
form tri-iodo-thyronine (T3)

104. Iodine is absorbed from entire alimentary
tract, particularly from small intestine
Iodine and iodate are converted into
iodide prior to absorption
Other mucous membranes and skin can
also absorb iodine
Absorption

105. Iodide absorbed from alimentary tract and
elsewhere enters the circulation
About one third is taken up by the thyroid
gland
The remainder is excreted, mainly by the
kidneys
Small amounts of iodide are excreted in
saliva, bile, milk, sweat and expired air

106. Plasma iodine level is 4-10 mg/dl
Only 10% of it is inorganic iodide
Organic iodine is present mostly in the
form of thyroid hormones
Thyroid hormones are bound to some
proteins (called protein bound iodine)

107. Daily requirement
Infants 40–50 µg/day
Children 70–120 µg/day
Adults 150 µg/day
Pregnant women 200 µg/day
Lactating women 250 µg/day

108. Iodine is present in water and soil
Foods, both animal and plant, obtain
iodine from water and soil
Iodine content of foodstuffs depends
upon iodine content of water and soil
Dietary sources

109. Sea water is rich in iodine
Sea foods, e.g. fish, oysters, lobsters etc,
are the best sources of iodine
As we go away from the sea, the iodine
content of water and soil, and hence that
of the foodstuffs, decreases

110. Iodine deficiency is common in certain
areas of the world
These areas constitute the so-called
goitre belt
Sub-Himalayan region of India is a part of
goitre belt since the iodine content of soil
and water is poor in this region
Iodine deficiency

111. Iodine deficiency results in goitre
(enlargement of thyroid gland)
Thyroid gland becomes hypertrophic in
order to produce enough hormones from
the available iodine
The goitre is generally non-toxic
(symptomless)

112. Goitre is endemic in the goitre belt areas
Goitre →

113. A severe deficiency of iodine can produce
hypothyroidism
Endemic goitre can be prevented by
providing iodized salt in the goitre belt

114. Iodized salt is prepared by adding
potassium iodate to common salt
Its iodine content should be 30 ppm (parts
per million) at the manufacturing stage
It is supposed to be at least 15 ppm when
it reaches the consumer

115. Govt. of India has made iodisation of salt compulsory

116. About 60-100 mg of copper is present in
an average adult
Relatively large amounts of copper are
present in muscles (30-50 mg), bones
(12-20 mg) and liver (9-15 mg)
Copper

117. Plasma copper level is 100-200 mg/dl
Nearly 90% of the plasma copper is
tightly bound to ceruloplasmin
The rest is loosely attached to albumin
Albumin is the major carrier of copper as
it can easily release copper

118. Copper performs its functions in the form
of copper-containing enzymes
These include cytochrome oxidase, super-
oxide dismutase, monoamine oxidase,
tyrosinase, dopamine b-hydroxylase etc
Ceruloplasmin also functions as ferro-
xidase which oxidises Fe+2 to Fe+3
Functions

119. Copper is also required for:
Synthesis of haemoglobin
Formation of bones
Maintenance of myelin
sheath of nerves

120. One third of dietary copper is normally
absorbed, mainly from small intestine
Copper-binding P-type ATPase transfers
copper from the lumen of the gut into
portal circulation
Copper-binding P-type ATPase is present
in intestinal mucosa and many other cells
Absorption

121. Albumin carries copper to liver
A different copper-binding P-type ATPase
is present in liver
This ATPase incorporates copper into
apo-ceruloplasmin

122. Adults require about 2.5 mg of copper
daily
Infants and children require about 0.05
mg/kg of body weight
Daily requirement

123. Dietary sources of copper
Liver Kidney Meat
Nuts Legumes Raisins

124. Disorders of copper metabolism
Inherited
disorders
include:
Wilson’s disease
Menkes’ disease

125. Wilson’s disease is also known as
hepato-lenticular degeneration
It is an autosomal recessive disease
Synthesis of ceruloplasmin is impaired in
Wilson’s disease
Wilson’s disease

126. There is no defect in the gene for cerulo-
plasmin
Apoceruloplasmin is synthesized normally
The genetic defect involves incorporation
of copper into apoceruloplasmin

127. There is congenital deficiency of copper-
binding P-type ATPase in liver
This causes copper toxicity by impairing:
Incorporation of copper into apo-
ceruloplasmin
Biliary excretion of copper

128. Large amounts of copper are deposited in
liver, basal ganglia and around cornea
Serum copper and ceruloplasmin levels
are very low
Urinary excretion of copper is increased

129. This is an X-linked recessive disease
Copper-binding P-type ATPase is
deficient in intestinal mucosa and most
other tissues but not in liver
Copper accumulates in intestinal mucosa;
it cannot be released into circulation
Menkes’ disease

130. Lack of absorption leads to deficiency of
copper in the tissues
The deficiency causes:
Cerebral degeneration
Hypochromic microcytic anaemia
Steely and kinky hair

131. Serum copper and ceruloplasmin
levels are elevated in:
• Pregnancy
• Infections
• Leukaemia
• Collagen diseases
• Myocardial infarction
• Cirrhosis of liver

132. The total amount of zinc in an average
adult is 1.3-2.1 gm
Its tissue distribution is very wide
Prostate, liver, kidneys, muscles, heart,
skin, bones and teeth have zinc in high
quantities
Zinc

133. Plasma zinc level is 50-150 µg/dl
Erythrocytes and leukocytes have a
higher concentration of zinc than plasma

134. Zinc is essential for normal growth and
sexual development
It is required for synthesis of nucleic acids,
which is essential for cell division and
growth
In the form of zinc fingers, it is a part of
some proteins which regulate transcription
Functions

135. Many enzymes require zinc for
their catalytic activity such as:
• Alkaline phosphatase
• Carbonic anhydrase
• Carboxypeptidase
• Glutamate dehydrogenase
• Lactate dehydrogenase
• Malate dehydrogenase
• Alcohol dehydrogenase etc

136. Zinc is present in the b-cells of the islets
of Langerhans
It is required for the storage and release
of insulin

137. Zinc is absorbed from the small intestine
Copper, cadmium and calcium interfere
with the absorption of zinc
Phytates also retard zinc absorption by
forming an insoluble complex with zinc
Absorption

138. Daily requirement
Age and sex Requirement
Infants 2-3 mg/day
Children 5-8 mg/day
Adult men 12 mg/day
Adult women 10 mg/day
Pregnant women 12 mg/day
Lactating women 12 mg/day

139. Meat
Dietary sources of zinc
Liver Kidney
Fish Eggs
Milk
Fish
Yeast
Whole grain
cereals

140. Dietary zinc deficiency may occur in
vegetarians taking refined wheat flour as
their staple diet
It can also occur in acrodermatitis entero-
pathica
Zinc deficiency

141. Zinc deficiency
causes:
• Retardation of
growth
• Dwarfism
• Delayed puberty
• Hypogonadism
A milder
deficiency may
cause:
• Poor wound
healing
• Impaired
perception of
taste

142. About one mg of cobalt is present in an
average adult
It is distributed chiefly in liver, kidneys and
bones
Cobalt is present almost entirely as a
constituent of vitamin B12
Cobalt

143. Inorganic cobalt doesn’t perform any
function in human beings
Inorganic cobalt is not absorbed from the
gut; injected cobalt is rapidly excreted
Cobalt functions solely as a component of
vitamin B12
It must be provided in the diet as vitamin
B12

144. About 12-20 mg of manganese is present
in an average adult
Liver, pancreas and kidneys contain
relatively more manganese than other
tissues
Manganese

145. Manganese is present mainly in the
mitochondria and nuclei of the cells
Manganese is absorbed from the small
intestine
Less than 5% of the ingested manganese
is normally absorbed

146. Manganese is required for:
• Formation of matrix of bones and
cartilages
• Normal reproduction
• Normal functioning of central
nervous system
• Stabilizing the structure of nucleic
acids

147. A number of enzymes require
manganese as a cofactor such as:
• Superoxide dismutase
• Arginase
• Acetylcholine esterase
• RNA polymerase
• Carboxylases
• Glycosyl transferases

148. The daily requirement of manganese is
2-5 mg
Whole-grain cereals, legumes, nuts,
green vegetables and fruits are good
sources of manganese

149. Molybdenum is present in very small
amounts in human beings, mainly in liver
and kidneys
It is a component of xanthine oxidase,
aldehyde oxidase and sulphite oxidase
Sulphite oxidase converts sulphite and
sulphur dioxide into sulphate
Molybdenum

150. The exact requirement for molybdenum is
unknown
An average diet provides 75-100 µg of
molybdenum a day
Molybdenum deficiency is unknown in
human beings
Excessive intake of molybdenum may
cause copper deficiency

151. The total amount of chromium in an
average adult is about 6 mg
It is widely distributed in the body
Chromium is a constituent of glucose
tolerance factor (GTF)
Chromium

152. GTF is a low molecular weight peptide
GTF binds to insulin receptor and
potentiates the actions of insulin
A relationship has been shown between
chromium deficiency and glucose
intolerance

153. Absorption of chromium is less than 1%
Stainless steel utensils contain chromium
which can be absorbed
Chromium intake is about 0.35 mg/day in
men and 0.25 mg/day in women which is
adequate
Excess chromium can be toxic

154. Selenium content of normal adult humans
varies widely
Values from 3 mg to 15 mg have been
reported in different geographical areas
About 30% of the total body selenium is
present in the liver, 30% in muscles, 15%
in kidneys, and 10% in blood
Selenium

155. Most of the selenium present in tissues is
present in proteins (selenoproteins)
Selenium performs its functions in the
form of selenoproteins, many of which
are enzymes
Four different glutathione peroxidases
have been identified, all of which contain
selenium

156. Glutathione peroxidase (GPx) is a part of
the anti-oxidant defence system
GPx can break down hydrogen peroxide
and fatty acid hydroperoxides
Both these are toxic compounds

159. Thus, the major role of selenium is as an
anti-oxidant
In this function, it complements the role of
vitamin E

160. Another role of selenium is in iodine
metabolism
Three different iodo-thyronine deiodinases
have been identified
These convert thyroxine (T4) into the more
active tri-iodo-thyronine (T3)
All the three are selenium-containing
enzymes

161. The two major forms of selenium in food
are selenomethionine and selenocysteine
Selenomethionine is found mainly in plant
foods and selenocysteine in animal foods
Their absorption is highly efficient
The main site of absorption is duodenum
Absorption and excretion

162. Selenium homeostasis is maintained
primarily through excretion
Selenium is excreted via urinary and
alimentary tracts
Urinary excretion is the primary route of
regulation under normal conditions

163. Different selenium requirements have
been recommended in different countries
In India, the recommended intake is 40
μg/day for adults of both sexes

164. The role of selenium deficiency in human
beings came to the fore in 1979
Selenium deficiency was correlated with
Keshan disease and Kashin-Beck disease
in China
These diseases were found in areas where
soil is severely deficient in selenium

165. Keshan disease results in cardiomegaly,
congestive heart failure and cardiac
necrosis
Kashin-Beck disease results in severe
osteoarthritis, and degeneration of
chondrocytes and nerves
Selenium supplementation was found to
protect people from these diseases

166. Fluorine naturally occurs as the
negatively charged fluoride ion
Only small amounts are present in
human beings (about 2.5 gm in adults)
More than 95% of fluoride is present in
bones and teeth
Fluorine

167. Fluoride is not physiologically essential
because it doesn’t perform any function
Still, it is considered as essential because
of its role in prevention of dental caries
Dental caries is a chronic disease caused
by cariogenic bacteria

168. Cariogenic bacteria are naturally present
in the oral cavity
They metabolize carbohydrates into
organic acids (pyruvic and lactic acids)
These acids can dissolve tooth enamel
This produces cavities in teeth (dental
caries)

169. Dental caries

170. Teeth are made up mainly of calcium
hydroxyapatite
Fluoride ions displace the hydroxyl ions
forming fluoroapatite
This hardens the tooth enamel, and
makes it resistant to dissolution
Fluoride ions also decrease acid
production by inhibiting bacterial enzymes

171. The fluoride content of most foods is very
low
Exceptions are tea, grape juice and
marine fish
Some fruits and vegetables may acquire
fluoride from fluoride-based pesticides

172. Main source of fluoride is drinking water
In tropical countries like India, water
intake is relatively high
Drinking water provides enough fluoride if
its fluoride content is 0.5-0.8 ppm (parts
per million)

173. If fluoride content of water is low, dental
caries becomes a public health problem
In such areas, fluoride must be added to
the source of drinking water (fluoridation)
The aim is to raise the fluoride content to
0.5-0.8 ppm

174. Excess of fluoride in drinking water is
harmful
If the fluoride content of water exceeds
1.5 ppm, it can cause fluorosis
If the excess is mild, only the teeth are
affected (dental fluorosis)
If the excess is severe, the bones are
affected (skeletal fluorosis)

175. In early stage, the teeth appear mildly
discoloured
Later on, stains ranging in colour from
yellow to dark brown appear on teeth
The surface of teeth becomes irregular
with noticeable pits
Dental fluorosis

176. Moderate fluorosis Severe fluorosis
Dental fluorosis
Normal teeth Mild fluorosis

177. Prolonged intake of excessive fluoride
affects the bones
The bones of vertebral column, pelvis and
limbs get deformed
There is calcification of ligaments and
tendons, immobility and muscle wasting
Skeletal fluorosis

178. Skeletal fluorosis can also result in
neurological problems
Neurological problems are caused by
spinal cord compression

179. Skeletal fluorosis

180. Fluorosis occurs in certain areas where
fluoride content of water is high
There are several such areas in the world

181. There are
some high-
fluoride areas
in India also
Defluoridation
of drinking
water is
required in
such areas