9
Minerals and Trace Elements
JJ (Sean) Strain and Kevin D Cashman
Key messages- This chapter defi nes the essential minerals and trace elements.
- It describes the functions and routes of metabolism within the
body of each of the minerals and trace elements in turn. - Dietary requirements and dietary sources are discussed for each
mineral.
© 2009 JJ Strain and KD Cashman.
- Health effects and symptoms of both inadequate and toxic
intakes are described. - Methods of assessing the body status of each mineral and trace
element are reviewed.
9.1 Introduction
Essential minerals, including the trace elements, are
inorganic elements (see Figure 9.1) that have a physi-
ological function within the body. These must be
supplied in the diet (food and fl uids) and vary from
grams per day for the major (macro) minerals through
milligrams to micrograms per day for the trace
elements.
It has been proposed that the environment (most
probably in the primordial sea around hydrothermal
vents) in which living organisms evolved was a
primary determinant of which elements became
essential for life by providing structural integrity and
catalytic ability to the fi rst complex organic mole-
cules. As life evolved from the oceans on to land, a
natural selection process may have resulted in some
elements becoming relatively more important because
of superior catalytic abilities over other elements. In
any event, the uneven distribution of elements in a
land-based environment meant that effi cient homeo-
static mechanisms had to be in place to conserve
essential elements and to eliminate excesses of essen-
tial and nonessential elements. The processes of
absorption from the gastrointestinal tract and excre-
tion with body fl uids, therefore, are major ways in
which the concentration and amount of an element
can be controlled in the body. In addition, storage in
inactive sites or in an unreactive form can prevent an
element from causing adverse effects in the body, and
release from storage can be important in times of
dietary insuffi ciency.
All elements have the potential to cause toxic symp-
toms, whereas some, the known essential elements
in Figure 9.1, have the potential to cause defi ciency
symptoms. Even so, defi ciencies of only four of these
inorganic elements are known to be prevalent in
human populations. Two of these defi ciencies, iodine
and iron, are widespread in human populations
whereas the other two, zinc and selenium, only occur
in some population groups under specially defi ned
conditions. Overt clinical signs of defi ciency of any
of the other inorganic elements are exceptional in
humans and mainly occur secondary to other clinical
conditions. Such observations do not preclude the
possibility that suboptimum status of the great major-
ity of the elements indicated in Figure 9.1 is impor-
tant in human nutrition. Indeed, there is an increasing
awareness of the potential role of suboptimal as well
as supraoptimal nutritional status of minerals and
trace elements in the development of degenerative
age-related diseases, such as coronary heart disease,
cancer, and osteoporosis. Moreover, other elements,
which currently have no published dietary recom-