The AIs given above are for individuals who are moderately active in temperate climates. As was discussed in Chapter 4, high levels of activity or exposure to high temperature or humidity results in increased needs for water to replace sweat losses. In these settings, additional sodium above the AI may be required as well, but experimental data are lacking, especially at dietary intakes of 1.5 g (65 mmol)/day.
Still, for most physically active individuals, the AI should be adequate. Of the 1.5 g (65 mmol)/day, only about 0.23 g (10 mmol) is needed to replace insensible losses, exclusive of sweat and urine, in acclimatized individuals. Hence, approximately 1.3 g (55 mmol) is available to replace sodium loss in sweat. This amount should be adequate even in unacclimatized, untrained individuals, depending on the duration of activity and exposure. However, for such individuals who are unacclimatized to a heavy heat load over long periods of time—such as that resulting from infrequent heavy physical activity at high temperature and humidity over several hours—additional sodium may be needed. As stated earlier, the AI does not apply to individuals who lose large volumes of sodium in sweat, such as competitive athletes and workers exposed to extreme heat stress (e.g., foundry workers and fire fighters). Sodium intake invariably rises with increased energy intake in physically active individuals and this increase usually is enough to compensate for sweat sodium losses. However, some individuals in the situations described above can lose excessively large amounts of sodium in sweat and on those occasions they should ingest a diet that contains sodium in excess of the AI.
Total iodine intake includes iodine that is naturally present in foods as well as iodine from iodized salt. While iodine from iodized table salt has been available in the United States and Canada since the 1920s, the extent to which iodized salt currently contributes to meeting iodine needs is unknown. Iodide was originally added to table salt in order to address the problem of endemic goiter, a problem found in the Great Lakes region and the Pacific Northwest. Previously, the food supply in these regions was limited to