Calcium Intake

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Calcium intake also varies widely according to the quantity and composition of the diet. Dairy products are a major source of calcium intake. Nuts, pulses, some green vegetables (broccoli) and seafoods as well as calcium from drinking water may further contribute. Daily calcium intake depends both on food selection and the total food/energy intake.

Athletes with low daily energy intake or those who follow a weight reduction programme may therefore have a marginal calcium intake. Females, especially long distance runners, have often been found to have calcium intakes that are lower than the RDA, probably as a result of relatively low energy intakes (37, 59, 84,131, 206). It has been reported (87) that a calcium intake of 1500 mg/day is required to achieve calcium balance in postmenopausal women not receiving oestrogen replacement therapy. Barr (9) concluded from these data that female athletes who are amenorrhoeic and have low oestrogen levels should ingest 1500 mg

Figure 34 Calcium intake in athletes increases with higher energy intakes. E, endurance athletes; S, strength athletes; T, teamsports athletes. Reproduced from Erp-Baart et al. (59), with permission from Georg Thieme Verlag, Stuttgart and New York

calcium/day. On this basis, all amenorrhoeic athletes (at risk groups include runners, dancers, gymnasts, bodybuilders) would have inadequate intakes.

PHOSPHATE

Phosphate is the counterpart of calcium in bone formation. About 85% of the total phosphate is present in the skeleton. The remainder is distributed between extracellular and intracellular space in soft tissue. Phosphate is an essential element in numerous enzymes as well as in energy metabolism (nucleotides and conjunction with B vitamins). Phosphate intake, and consequently supply to the blood, is known to affect bone formation. Therefore, the intake of phosphate and calcium should be balanced. The fractional phosphate absorption in the gut is approximately 70%, which is about twice as high as that of calcium absorption (131). Phosphate is mainly excreted in the urine, the unabsorbed fraction in the intestine leaves the body with the faeces and minor amounts are lost with sweat.

Influence of Exercise

Exercise that leads to a substantial sweat loss results in haemoconcentration, which in turn will elevate plasma phosphate levels. Phosphate losses through sweat are negligible. In addition, changes in alkalosis (inducing a fall in phosphate levels), acidosis and cell damage (inducing an increase in phosphate levels) are known to influence plasma levels (104).

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