chloride together.⁴ Sodium and chloride are required to maintain extracellular fluid volume and serum osmolality. Human populations have demonstrated the capacity to survive at extremes of sodium intake from less than 0.2 g (10 mmol)/day of sodium in the Yanomamo Indians of Brazil to more than 10.3 g (450 mmol)/day in Northern Japan. The ability to survive at extremely low levels of sodium intake reflects the capacity of the normal human body to conserve sodium by markedly reducing losses of sodium in urine and sweat.

Under conditions of maximal adaptation and without sweating, the minimal amount of sodium required to replace losses is estimated to be no more than 0.18 g (8 mmol)/day. Still, it is unlikely that a diet providing this level of sodium intake is sufficient to meet dietary requirements for other nutrients. Given that dose-response data are lacking regarding the level of sodium and chloride intake from currently available foods in the United States and Canada at which half of the individuals in a group would have their needs met for other essential nutrients (which would be necessary to develop an EAR), an AI was developed instead.

The AI for sodium is set for young adults at 1.5 g (65 mmol)/day (3.8 g of sodium chloride) to ensure that the overall diet provides an adequate intake of other important nutrients and to cover sodium sweat losses in unacclimatized individuals who are exposed to high temperatures or who become physically active as recommended in other DRI reports. This 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.

The AI for sodium for older adults and the elderly is somewhat less, based on lower energy intakes, and is set at 1.3 g (55 mmol)/ day for men and women 50 through 70 years of age, and at 1.2 g (50 mmol)/day for those 71 years of age and older (see Table S-4).