Essentiality and Toxicity for Man

Essentiality and Toxicity for Man For humans, sodium (and chlorine) are essential nutrients, the deficiency of which frequently and acutely leads to premature death, usually from circulatory failure. The second most frequent consequence is diarrhea. The physiology of man is, consequently, characterized by multiple control mechanisms which act to maintain and control the NaCl content and concentrations within the body. Sodium deficiency symptoms in humans are not well known nonetheless, a sodium chloride deficit as a common cause of death is quite treatable with minimum effort, provided that some basic principles are remembered. Body weight change is the best indicator of a sodium deficit. Except in the presence of imminent circulatory collapse, oral treatment is usually possible. Except in case of cholera, the colon usually responds to aldosterone, and quite low sodium concentrations are adequate for the rehydration solutions. In the case of cholera, near-isotonic solutions are necessary (Harper et al. 1997). 

The normal sodium concentration in human serum or plasma is 136- 

Sodium comprises -90% of the cations present in plasma. By contrast, the normal intracellular sodium concentration is generated and controlled by various types of channel proteins such as Na , K -ATPase and Na -glucose cotransporters inserted into the cell membrane, and these play an important role in the transmission of nerve impulses and translocation of biorelated substances across the cell membrane. The normal sodium ion concentrations in body fluids are listed in Table 1.2-12. 

Sodium deficiency during long-term endurance exercise may cause dehydration. A sodium content of 300-800 mg in saliva seems to provide an adequate sodium supply during endurance exercise, without impairing the flavor of beverages (Zapf etal. 1999). The importance of taste to individuals on a low-sodium diet has been demonstrated. It is interesting to observe that a low-sodium diet maintained over a long period leads to a shift in preference toward less salty foods (Bertino et al. 1982). 

Erom a physiological viewpoint, sodium provides the bulk of osmotically active sol- 

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