tion and bone metabolism and these have been
summarized in the US Surgeon General’s Report
on Nutrition and Health (1988) (see Chapter 7).
Exercise and calcium balance
Acute exercise results in a prompt increase in
serum calcium, both in its ionized and non-
ionized forms. This may be due in part to lactic
acidosis rather than to changes in PTH and calci-
tonin concentrations, and haemoconcentration is
also likely to be a significant factor (Vora et al.
1983; Cunningham et al. 1985). Marathon
running was found to be accompanied by a tran-
sient decrease in urinary calcium and serum
osteocalcin levels (Malm et al. 1992). Endurance
322 nutrition and exercise
training has been reported to be associated with
increased serum levels of the active form of
vitamin D, leading to increased calcium absorp-
tion and a rise in total body calcium (Yeh & Aloia
1990). A few studies have demonstrated exercise-
related elevations in PTH (Ljunghall et al. 1985,
1986; Salvesen et al. 1994), but this has not been
confirmed in other studies (Aloia et al. 1985).
The influence of calcium intake and physical
activity on peak bone mass has been the subject
of much attention (Kanders et al. 1988; Mazess &
Barden 1991; Recker et al. 1992). There are both
cross-sectional and longitudinal studies that
favour a beneficial effect of calcium on the adult
skeleton and there are others that find no rela-
tionship between dietary calcium and bone mass
and rate of bone loss. Peak bone mass is achieved
during the third decade of life. Apart from
calcium intake, heredity is also an important
factor determining peak bone mass. A study on
identical twins, where one twin in each pair
received calcium supplementation and the other
a placebo, suggested that extra calcium in the
diet is beneficial to the achievement of peak bone
mass prior to puberty (Johnston et al. 1992).
The role of physical activity in optimizing
bone growth as well as maintaining bone mass is
well established (Torgerson et al. 1995): acute
reductions in weight-bearing activity are associ-
ated with a dramatic loss of calcium. Measure-
ments of prolonged bed rest in healthy
volunteers and in patients, as well as in astro-
nauts subjected to microgravity, have all shown
an increased calcium loss and a reduced skeletal
mass (Anonymous 1983). Increased physical
activity, and in particular running, has been
shown to be associated with an increased bone
density (Lane et al. 1986), and it seems clear that
the physical stress imposed on the bone is an
important factor (Lanyon 1992; Wolman 1994).
This is supported by a recent study showing
increases in bone area in adult male rats sub-
jected to a resistance training programme
(Westerlind et al. 1998). There is, however, little
information on the type, frequency, duration and
intensity of exercise that will optimize bone mass
and minimize the age-related loss.Fig. 23.1Most forms of exercise are good for bone
health and should be encouraged in youngsters. Only
a few athletes, most commonly young women in
sports where low body mass confers an advantage, are
likely to suffer accelerated bone mass. Photo ©
Allsport / M. Powell.