usually in the form of reindeer liver. Hasunen and Pekkarinen (1976) also reported that Finnish Skolt (a subpopulation of the Lapps) children consumed amounts of vitamin A well in excess (two- to fourfold) of the RDA. Rodahl and Issekutz (1965) reported that Alaskan Eskimos consumed approximately twice as much vitamin A as did U.S. Army or Air Force personnel living under similar conditions (3,750 versus 1,900 µg RE, respectively, or 3.6- and 1.9-fold higher than the RDA, respectively). Thus, indigenous persons living in the higher latitudes of the world continue to demonstrate comparatively high dietary intake of vitamin A.

Compared to the 1989 RDA (NRC, 1989), it was reported that subjects in the 38-d Operation Everest II consumed increased amounts of vitamin A (Rose et al., 1987) as did subjects during an exercise at 3,500 to 4,050 m (11,475 to 13,279 ft) altitude in Bolivia (Edwards et al., 1991). However, Hannon et al. (1976) reported a transient reduction in the consumption of vitamin A by eight women during a sojourn to 4,300 m (14,098 ft) altitude. In addition to a decreased intake, it has been suggested that a malabsorption of fat may occur at high altitudes (Boyer and Blume, 1984; Ward et al., 1989b). This interpretation of the data has been criticized because two of the three subjects were reported to have been fat malabsorbers at sea level altitude prior to the experiment. Thus, it is not known whether impaired intestinal fat absorption occurs at high altitude, and if it does, whether it would be sufficient to affect absorption of the fat-soluble vitamins.

Caution is recommended regarding the consumption of even modest supplements of vitamin A by persons working in cold or high-altitude environments due to the mobilization and utilization of body fat that often occurs under these circumstances and the resultant release of vitamin A stores into the circulation.

It has been reported that 6 months to 2 years is required for a person consuming a vitamin A-deficient diet to become deficient. Thus, there is little justification to recommend intakes of vitamin A above RDA or MRDA levels because most expeditions or maneuvers are of a much shorter duration than the time required to become deficient. Deficiency of the vitamin is initially characterized by a reduction in night vision and dark adaptation, symptoms that are readily noticed by the person involved. Only under such instances of suspected vitamin A deficiency should a supplemental regimen of no more than the current RDA of 1,000 µg RE (NRC, 1989) be considered. Administration of supplemental vitamin A to a person with an adequate vitamin A status does not improve night vision further. Therefore, the suggested micronutrient intake goal for vitamin A is set at the RDA and MRDA level of 1,000 µg RE (Table 13-1). This recommendation is in contrast to the Thomas et al. (1993b)