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(Hannon et al., 1976). Pugh (1965) reported that two climbers who kept a cursory food journal while climbing from 6,400 to 7,600 m (20,984 to 24,918 ft) altitude on Mount Everest consumed 500 and 750 mg of calcium. Rupp et al. (1982) measured a variety of electrolyte changes in blood and urine of members of a Kanchenjunga expedition. They reported a slight, transient (8 percent) decrease in plasma calcium at higher altitudes, which returned to normal within a few days at altitude.

During the 9-wk On Top Everest '89 nutrition research expedition, the 15 members (10 males, 5 females) maintained full dietary records every day, regardless of their camp location. While some of the records were inadvertently lost, there were a total of 842 dietary records collected (out of a possible 945, for an 89 percent completion rate) and analyzed for intake of energy and various nutrients. The calculated intake of calcium was 910 ± 579 mg/d, with no changes or trends occurring as a result of increasing altitudes.

During this expedition, 24-h urine samples were collected at 28 separate times and analyzed for various compounds. Urinary excretion of calcium and of hydroxyproline, both markers for bone demineralization, were within normal ranges, which suggests that there was no loss of calcium. Also, single and dual photon absorptiometry performed immediately prior to departure from the United States, and at approximately 4 weeks following return to the United States, showed no indication of bone demineralization during exposures to these high altitudes.

Author's Recommendation

Because intakes of calcium have been reported to be near that suggested by the RDA and there have been no indications of an inadequate intake or adverse change in status of calcium during the 9-wk period at high and extreme altitude, there is no basis for recommending the micronutrient intake goal of calcium above the current RDA and MRDA levels of 800 to 1,200 mg/d (Table 13-1).

Phosphorus
Functions

Phosphorus is required for bone formation and integrity, with approximately 85 percent of the total phosphorus in the adult body localized in the bones (NRC, 1989). Phosphorus is involved also in energy metabolism in its role as an enzyme modulator and its essentiality for high-energy bonds in ATP and creatine phosphate.



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