ciencies in athletes are invalid for methodologi-
cal reasons: a shortfall in recommended intake
relative to published recommended intakes is
not indicative of a deficiency (van der Beek 1991,
1994; Chen & Wu 1996). Athletes with a balanced
diet should receive the RDA provided energy
intake is sufficient to balance expenditure
(Shoorland 1988; Rokitzki et al. 1994a), although
it must be recognized that not all athletes have a
high energy intake, and not all eat a varied diet.
Unfortunately, there are limited and conflicting
data with regard to the micronutrient status of
physically active individuals (van der Beek 1985;
Belko 1987; Fogelholm 1992). Methods for the
assessment of vitamin status are often inade-
quate, as outlined in the preceding chapter.
Dietary surveys and food records have been used
to assess the vitamin status of athletes, but tables
of vitamin content are inherently unreliable, and
the vitamin loss attributed to vitamin availabil-
ity, processing, storage, and preparation of the
foods is often not taken into account. Blood or
other tissue levels of vitamins are affected by
several factors including acute exercise and they
may not be entirely accurate as measures of the
nutritional status of athletes; caution should
therefore be taken in interpreting the results
(see Chapter 20). Furthermore, the RDAs are
designed primarily to avoid nutritional deficien-
cies and do not focus on exercise or stressful
environments. The RDA is determined by
various professional bodies to designate the level
of intake of a micronutrient that will meet the
known nutritional needs of practically all
healthy persons (Armstrong & Maresh 1996),
and is based on an average-sized person with an
average amount of physical activity and an
average physiological requirement. This is then
adjusted by a variable factor to compensate for
incomplete utilization by the body, the variation
in requirements among individuals and the
bioavailability of the nutrients from different
food sources (US National Research Council
1989). The definition of RDA is not identical for
all nations and organizations (van der Beek
1991).
282 nutrition and exercise
It is not clear that the RDA established for
the general population may apply to athletes,
labourers, or soldiers in heavy training
(Shoorland 1988). There have been few reports
on the setting of separate RDAs for athletes
(Yakovlev 1957; Sports Science Committee of
Japanese Association 1977; Grandjean 1989;
Chenet al. 1992). The majority of dietary surveys
conducted on athletic population clearly indi-
cated that the vitamin intakes of all but a small
minority of athletes exceed the RDA levels if a
well-balanced diet is typically consumed (Sobal
& Marquart 1994). Although vitamin intakes of
less than the RDA do not indicate vitamin defi-
cienciesper se, the further the intake falls below
the RDA, the greater is the risk of developing a
deficiency state.
Athletes have been targeted as a significant
group for vitamin supplements, and dietary
surveys and questionnaires of athletes confirm
the widespread use of the vitamin supplements.
Questionnaires completed by 2977 college and
high school athletes have found that 44% of those
surveyed took one or more vitamin supplements
(Parret al. 1984). In other, smaller surveys, 31% of
80 Australian athletes and 29% of 347 non-elite
runners (Nieman et al. 1989) and 42–43% of foot-
ball players, gymnasts and runners (Sobal &
Marquart 1994) took vitamin supplements. Some
studies have documented even higher percent-
ages of athletes taking supplements, including
71% of female runners (Clark et al. 1988) and
100% of female bodybuilders (Lamar-
Hildebrandet al. 1989). Supplementation is pur-
ported to enhance performance, delay fatigue,
and speed up recovery by some ill-defined
ergogenic mechanism. Despite the lack of evi-
dence that large intakes of vitamin have positive
effects on performance, many athletes are still
taking vitamin supplements, because of a lack of
nutritional knowledge and lack of familiarity
with the dietary guidelines, and quite a number
take very large doses. The concern is that not
only the amounts of supplementation can be
financially costly because of the large doses of up
to 5000 times the recommended levels, but there