The Skeletal System and Its Movements 7predominates, resulting in loss in bone density and
osteoporosis. However, for normal bone growth to
proceed in children, and for normal peak mineral
mass to develop in young adulthood, adequate
dietary intake of calcium and other nutrients is essen-
tial. Furthermore, even if there is adequate calcium
available and normal peak bone density is achieved,
osteoporosis develops earlier, tends to be more
severe, and is four times more common in women
than men (Dudek, 1997). In terms of gender, adult
females generally begin with about 30% less bone
mass than men (Rasch, 1989), start decreasing bone
density at an earlier age, and lose bone at a greater
rate than males. Osteoporosis affects approximately
40% of women after the age of 50 (Hall, 1999); and
in elderly females, spinal bone density is often 40%
of that at 20 years of age (Abernethy et al., 2005).
At age 80, women have one chance in five (Kenney,
1982) of sustaining a fracture of the hip (neck of the
femur), and osteoporosis-related fractures and asso-
ciated complications are among the leading causes
of death in the elderly population (Hall, 1999).
Unfortunately, this vulnerability of women to
osteoporosis is of particular concern to dancers,
and not just in later life. Although moderate activity
has been shown to increase bone density, strenuous
physical training combined with other factors still
under investigation, such as low energy availability,
extremely low percentage body fat, or failing to
menstruate normally, can result in loss of bone den-
sity rather than a gain in bone density (Myszkewycz
and Koutedakis, 1998; Williams, 1998). Estrogen
appears to be protective for bone density, and so
dancers who are low in estrogen production or not
menstruating (athletic amenorrhea) would be at risk
for lower bone density. This risk for early bone loss
is heightened by the common tendency for dancers
to smoke cigarettes and ingest large quantities of caf-
feinated beverages, including soft drinks (Clippinger,
1999). This loss of bone density, part of the female
athlete triad (American College of Sports Medicine,
1997), can occur with dancers as young as in their
teens, resulting in losses in bone density normally
not seen until after the fifth decade and markedly
increasing susceptibility to stress fractures (Khan et
al., 1999). Some of this loss in bone density may be
irreversible, and loss of bone density in young danc-
ers is particularly concerning when one realizes that
approximately 50% of bone mineralization and 15%
of adult height are normally established during the
teenage years (Hall, 1999).
Hence, dancers should be particularly conscien-
tious about eating a nutrient-dense diet with ade-
quate caloric and calcium content. Recommended
daily calcium intakes vary, according to source,
gender, and age, between 800 and 1,500 milligrams;
and a 1994 National Institutes of Health consensus
panel recommends 1,200 to 1,500 milligrams daily
for young adults between the ages of 11 and 24
years (Beck and Shoemaker, 2000; Clark, 1997).
One of the easiest ways to obtain adequate levels of
calcium is to regularly ingest three or four servings
of milk products per day. Any of the following foods
provides about 300 milligrams of calcium: 8 ouncesMeasurement of Bone Density
Various tests can be used for detecting osteoporosis through the measurement of bone density. In
the 1940s, plain X rays were used (Kaufman, 2000). However, since demineralization of bone is not
apparent until about 40% of the bone has been lost, other methods have been developed that are more
sensitive and can detect changes at a much earlier stage. One of the more precise tests currently used
is termed dual-energy X-ray absorptiometry (DXA). This method uses X-ray beams that have two distinct
energy peaks—one that will be absorbed more by soft tissue and the other by bone. This allows for
the soft tissue component to be subtracted and the bone mineral density to be determined. However,
many other tests are also available, some of which are less expensive and more accessible. In dancers,
testing of multiple sites is often recommended, as results from various sites may differ (Khan et al.,
1996). For example, due to the frequent loading of the lower extremity associated with dancing, the
bone density in the femur might appear normal while a site in the upper extremity may be low. Dancers
who have amenorrhea or have other reason for concern should discuss with their attending physicians
what their concerns are, whether testing is indicated, and what test would be best for them.