dium loss (Gardenswartz and Berl, 1981). In some elderly individuals with diabetes, hyporeninemic hypoaldosteronism may increase renal sodium loss (Schambelan et al., 1972). These individuals are usually identifiable by elevated serum potassium concentrations.
There has been limited research on sodium requirements for normal growth and development in humans. Growth failure has been recognized in young children with salt-wasting disorders, such as isolated hypoaldosteronism (Rosler, 1984), thus linking the need for adequate sodium in early life to normal growth. The addition of sodium to infant formula and its presence in commercially processed weaning foods has been the focus of debate since the 1970s. Issues debated have been the extent to which sodium is required in infancy for normal growth and the possibility that adult hypertension results from excess sodium intake during early years (Dahl, 1968; de Wardener and MacGregor, 1980). However, while animal studies indicate that sodium is required in normal growth of neonatal rats (Fine et al., 1987; Orent-Keiles and McCollum, 1940) and pigs (Alcantara et al., 1980), no studies were found that evaluated the effects of varying intakes of sodium on growth or other effects in normal, full-term human infants.
For preterm human infants, the few available studies indicate that sodium is indeed required for normal growth (Al-Dahhan et al., 1984; Bower et al., 1988; Chance et al., 1977). Two of these studies were conducted primarily in preterm infants (Al-Dahhan et al., 1984; Chance et al., 1977), while the other was among early and preterm infants with ileostomies (Bower et al., 1988).
When preterm infants born before 34 weeks gestation were given 92 to 115 mg of sodium per kg/day from 4 to 14 days postpartum, there was improved weight gain compared with infants who received 23 to 34 mg/kg/day of sodium (Al-Dahhan et al., 1984). When very-low-birth-weight premature infants were supplemented with sodium, weight gain was increased in a second study (Chance et al., 1977). Measurement of body water space and dynamic skinfold thickness indicated that the weight gain was partially due to water retention, with the remaining due to increases in lean body mass.
Sodium balance and growth was studied in 11 infants born fol-