Introduction
Calcium is a micronutrient with great impor-
tance to many cellular events in different tissues
in the body, as well as forming the major struc-
tural component of bone. Athletes are often con-
cerned that their normal diet will not provide
sufficient micronutrients, and the need for an
adequate dietary intake of calcium is as much a
concern for athletes as it is for the general popu-
lation. Augmentation of the diet with specific
calcium supplements and with calcium-enriched
foods is common practice among athletes and
non-athletes alike, but there is limited informa-
tion as to whether the need for calcium is
increased by physical activity, and whether such
supplementation is warranted.
The US Surgeon General’s Report (1988) states
that ‘inadequate dietary calcium consumption in
the first three to four decades of life may be asso-
ciated with increased risk for osteoporosis in
later life due to a low peak bone mass’. Osteo-
porosis is a chronic disease characterized by a
progressive loss of bone mass: it affects women
more than men, partly because of the role played
by a falling oestrogen level after the menopause.
Bone loss is widely accepted as a normal part of
the ageing process, and occurs at a rate of about
0.5–1.0% per annum after the age of 40 (Cohn
et al. 1976): by age 90, one third of women and
one sixth of men will have suffered hip fractures
as a consequence. However, a number of nutri-
tional and lifestyle factors have a major impact
on the rate of mineral loss from the skeleton:
these factors can be important in slowing
this process, and thus in delaying the point at
which the bone mineral density becomes so low
that the fracture threshold is easily exceeded.
Other important factors reported to be associated
with the maintenance of bone health are an
adequate level of physical activity and avoidance
or cessation of cigarette smoking and excess
alcohol intake. However, while there is a clear
role for physical activity in maintaining bone
mass, very high levels of exercise in women have
been associated with some degree of bone loss
(Drinkwateret al. 1990), so there are clearly a
number of issues of importance for women,
and perhaps also to a lesser extent for men,
involved in sports where high training loads are
involved.Roles of calcium in the body
Calcium is an essential nutrient and a major com-
ponent of mineralized tissue and is the mineral
found in the largest quantity in the body, repre-
senting about 1.5–2% of body mass in the
average adult: for men, total body calcium
content is about 1000–1100 g, and for women,
about 800 g (Cohn et al. 1976). Approximately
99% of the total body calcium is located in the
bones. The remaining 1% is accounted for by the
calcium found in the blood, muscle and nervous
tissue where calcium is necessary for blood coag-
ulation, muscle contraction and nerve conduc-
tion: although the amounts are small, the role of
calcium is crucial for normal functioning.