Introduction to Human Nutrition

Minerals and Trace Elements 189

mendations but are highlighted in Figure 9.1, might
prove to be essential for the optimum health and well-
being of humans.
Major constraints to the elucidation of the poten-
tial roles of minerals and trace elements in the onset
of degenerative diseases include diffi culties in assess-
ing status, and thereby defi ning requirements, and
myriad interactions among minerals and other nutri-
ent and nonnutrients in the diet. Sometimes, natural
experiments of genetic disorders can throw light on
the potential roles of minerals in disease processes
and these will also be discussed as appropriate in the
following sections.

9.2 Calcium

Calcium is a metallic element, fi fth in abundance in
the Earth’s crust, of which it forms more than 3%.
Calcium is never found in nature uncombined; it
occurs abundantly as chalk, granite, eggshell, sea-
shells, “hard” water, bone, and limestone. The metal
is used as a reducing agent in preparing other metals
such as thorium, uranium, and zirconium, and is
used as a deoxidizer, disulfurizer, or decarburizer for

various ferrous and nonferrous alloys. It is also used

as an alloying agent for aluminum, beryllium, copper,

lead, and magnesium alloys. Calcium was among the

fi rst materials known to be essential in the diet. All

foods of vegetable origin contain small but useful

amounts of calcium. Animals concentrate calcium

in milk, and milk and dairy products are the most

important food sources of calcium for many human

populations.

Absorption, transport, and

tissue distribution

The adult human body contains about 1200 g of

calcium, which amounts to about 1–2% of body

weight. Of this, 99% is found in mineralized tissues,

such as bones and teeth, where it is present as calcium

phosphate (together with a small component of

calcium carbonate), providing rigidity and structure.

The remaining 1% is found in blood, extracellular

fl uid (ECF), muscle, and other tissues.

Calcium is under close homeostatic control, with

processes such as absorption, excretion and secretion,

and storage in bone being involved in maintaining the

concentration of ionized calcium in the plasma within

1a

1

H

3

Li

11

Na

19

K

37

Rb

55

Cs

87

Fr

8 1b 2b 3b 4b 5b 6b 7b 8b

5

B

13

Al

6

C

14

Si

7

N

15

P

8

O

16

S

9

F

17

Cl

32

Ge

33

As

34

Se

35

Br

50

Sn

53

I

31

Ga

2

He

10

Ne

18

Ar

36

Kr

54

Xe

86

Rn

85

At

84

Po

83

Bi

82

Pb

49

In

81

Tl

51

Sb

52

Te

2a 3a 4a 5a 6a 7a

4

Be

12

Mg

20

Ca

38

Sr

56

Ba

88

Ra

23

V

41

Nb

73

Ta

105

25

Mn

43

Tc

75

Re

24

Cr

74

W

106

42

Mo

26

Fe

76

Os

44

Ru

30

Zn

80

Hg

48

Cd

27

Co

77

Ir

45

Rh

28

Ni

78

Pt

46

Pd

29

Cu

79

Au

47

Ag

21

Sc

39

Y

57

La

89

Ac

22

Ti

40

Zr

72

Hf

104

Lanthanides^71

Lu

70

Yb

69

Tm

68

Er

60

Nd

62

Sm

61

Pm

63

Eu

67

Ho

64

Gd

65

Tb

66

Dy

58

Ce

59

Pr

Actinides Th^9091 Pa^92 U Np^93 Pu^94 Am^95 Cm^96 Bk^9798 Cf Es^99100 Fm^101 Md^102 No^103 Lr

Figure 9.1 The periodic table of the elements. The widely accepted or putative essential elements are encircled.