NUTRITION IN SPORT

(Martin Jones) #1

(Reckeret al.1992). The combination of subopti-
mal calcium intakes by female athletes (Chen
et al.1989; Steen et al.1995; Peters & Goetzsche
1997) and differences of opinion regarding rec-
ommended dietary guidelines for this mineral
(Health and Welfare Canada 1983; National
Research Council 1989; Department of Health
1991) prompts some concern and questions
among those who care for, work with or feed
female athletes.
Why should one have concern? Since physical
activity, particularly high impact, is associated
with greater bone density (Dook et al.1997), one
might expect that female athletes need not worry
about the possibility of bone loss. However, iden-
tification of a syndrome of disordered eating,
amenorrhoea and reduced bone density (Loucks
1987) overshadows this positive aspect of physi-
cal activity and may contribute to a greater con-
sideration for adequate calcium intakes in female
athletes.
The important questions regarding calcium
are:
1 What is an optimal calcium intake to promote
and support adequate bone density in a female
athlete?
2 How can suboptimal calcium intakes be
improved?
The answer to the first question is currently
unknown. Differences of opinion regarding
optimal calcium intakes for adults exist among
countries, agencies and researchers. Even though
physical activity has been identified as a positive
factor in promoting greater bone density, no one
has identified either the optimal level of exercise
or calcium intake to support adequate bone
density in the female athlete. To recommend an
appropriate level of calcium intake, one needs to
rely on a thorough nutritional, exercise and
medical history of the athlete. Answers to ques-
tions about the following will provide added
perspective on whether to recommend the
dietary guideline for calcium or potentially a
higher level.



  • Family history of osteoporosis

  • Typical intake of calcium, fluoride, other bone-
    related minerals, protein and energy

  • Training intensity and type of sport


424 special considerations



  • Menstrual history and current status

  • Supplement and/or drug use and any malab-
    sorption conditions
    For the athlete who avoids calcium-rich foods
    or is restricting energy intake to lose weight,
    discussion of low-fat calcium-rich foods, food
    choices not normally recognized as calcium-rich
    or those that are fortified with calcium, e.g.
    calcium-fortified orange juice, is recommended.
    Consumption of a mineral water that has a high
    calcium content may also be appropriate for a
    possible source of dietary calcium (Couzy et al.
    1995).
    The second choice would be that for supple-
    mentation of the female athlete’s diet with
    calcium tablets. Determination of the typical
    calcium intake from food will help determine the
    appropriate level of supplement to recommend.
    However, supplementation with minerals is
    not without potential adverse effects. Wood and
    Zheng (1997) report that high dietary calcium
    intakes during a 36-day study reduced zinc
    absorption in healthy postmenopausal women.
    Limitations of the study include that activity
    level was not reported for the subjects and
    that differences will exist in nutrient absorption
    between a postmenopausal female and a young
    female. Cook et al.(1991) reported calcium sup-
    plements could inhibit the absorption of ferrous
    sulphate when consumed with food, although
    Reddy and Cook (1997) found no significant
    influence of calcium intake on non-haem iron
    absorption when varying levels of calcium
    (280–1281 mg · day–1) were consumed as part of
    the diet.
    In general, most experts agree that a calcium-
    rich diet is the most appropriate dietary prescrip-
    tion to promote and support optimal bone
    density. If this is not possible, consideration for
    low to moderate levels of a calcium supplement
    in addition to the dietary calcium intake to meet
    optimal levels is reserved for an alternative
    action.
    The relationship between the macrominerals
    and microminerals warrants more attention as
    athletes look to supplementation as solutions to
    their possible dietary inadequacies. Lukaski
    (1995) has expressed concern for the adverse

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