these vitamins (Weight et al. 1988b; Guilland et al.
1989; Fogelholm et al. 1992). Serum vitamin A
levels of 5% of 182 athletes investigated had a
value of less than 30mg·dl–1(Chenet al. 1992).
There has been no evidence of serious biochemi-
cal deficiencies of vitamin A existing in athletes.
It is unlikely that vitamin A supplementation will
enhance performance. Vitamin A supplementa-
tion is not necessary for athletes on an adequate
diet (Williams 1985; Clarkson 1991). Whether the
antioxidant role of b-carotene can reduce exercise
damage due to free radical activity remains to be
studied.
Vitamin A is one of the fat-soluble vitamins
and hence may be stored in the body for consid-
erable periods of time, unlike water-soluble vita-
mins. Overdosage over a period of time may
cause a condition known as hypervitaminosis,
characterized by anorexia, hair loss, hypercal-
caemia, and kidney and liver damage (Aronson
1986). Sustained daily intakes exceeding 15 000
mg · day–1of retinol can produce signs of toxicity
(US National Research Council 1989). However,
high doses of b-carotene are not generally con-
sidered to be toxic (US National Research
Council 1989; Clarkson 1995). Bodily stores are
available for short-term deficiency periods, and
thus, no significant decrements would be
revealed during short periods of reduced dietary
intake of vitamin A. Good sources of vitamin A in
the diet include liver, fish liver oils, butter, whole
milk, cheese and egg yolk. Rich sources of the
carotenoid are dark-green leafy vegetables, the
yellow or orange fruits and vegetables (see
Chapter 20).
Vitamin D
Vitamin D represents any one of several sterol
compounds in the body; vitamin D 2 (ergocalcif-
erol) is the result of the irradiation of ergosterol.
D 3 (cholecalciferol) is the naturally occurring
compound in the skin, formed by exposure to the
sunlight. The major function of vitamin D is its
hormone-like action in the process of mineraliza-
tion of bones and teeth and the regulation of
calcium metabolism. It promotes absorption of
288 nutrition and exercise
calcium from the intestine and helps to prevent
calcium deficiency. The RDA for vitamin D is
5 mg · day–1 for adults (US National Research
Council 1989), and no separate recommenda-
tions appear to have been made for athletes.
Overdoses of vitamin D are potentially toxic and
result in hypercalcaemia and hypercalciuria (US
National Research Council 1989). Levels of five
times the RDA are considered dangerous; intakes
of 50mg · day–1(2000 IU · day–1) for a prolonged
time may pose considerable risk. Hypervita-
minosis D leads to loss of weight, vomiting,
nausea, lethargy and loss of muscle tone; calcium
released from the bones may deposit in the soft
tissues, in the walls of the blood vessels and in
the kidneys.
Vitamin D deficiencies are rare in athletes with
adequate intake of dairy products and exposure
to sunlight, but those who have inadequate milk
consumption and lack of sunshine may be at
some risk for inadequate vitamin D nutriture. No
known controlled research has been conducted
on the role of vitamin D in physical performance
(Van der Beek 1991). The role of vitamin D in pro-
viding calcium for newly forming muscle tissue
is not clear and needs further investigation
(Clarkson 1991). Vitamin D is present in fish liver
oil and milk fortified with vitamin D (see
Chapter 20).Vitamin E
Vitamin E is a fat-soluble vitamin. Its activity is
derived from a number of tocopherols, the most
active one of which is a-tocopherol. Vitamin E
functions as an antioxidant of polyunsaturated
fatty acids in cellular and subcellular mem-
branes, and thus it serves as a free radical scav-
enger to protect cell membranes from lipid
peroxidation. The RDA for vitamin E is 8–10 mg
ofa-tocopherol · day–1. Vitamin E is relatively
non-toxic up to 800 mg · day–1 (US National
Research Council 1989). Dietary records showed
that between one third and one half of the ath-
letes investigated consumed less than two thirds
of the RDA (Loosli et al. 1986; Guilland et al.
1989). Guilland reported that the mean vitamin E