Little information is available on the effects of sodium on blood pressure in infants. The effect of two levels of dietary sodium on blood pressure and dynamic skinfold thickness was examined in 124 infants (Bernstein et al., 1990). Newborn infants were fed one of three diets: 43 infants were exclusively fed human milk (0.15 g of sodium [6.6 mmol]/L), 42 infants were fed a low sodium formula containing 0.23 g of sodium [10.2 mmol/L]), and 39 infants were fed a formula containing 0.31 g of sodium (13.9 mmol)/L. There were no significant differences among the three groups for either dynamic skinfold thickness or blood pressure at 6 weeks of age.
The data on the role of sodium intake during infancy on blood pressure in later years are also very limited. The most rigorous study was conducted with infants in Holland with a subsequent follow-up 15 years later. In this randomized, controlled trial of 476 Dutch infants fed a usual (≈ 0.33 g [≈ 14.3 mmol]/day) or low sodium (≈ 0.12 g [≈ 5.1 mmol]/day) formula, there was a small but significant reduction in blood pressure at 6 months among infants fed the low sodium formula (Hofman et al., 1983). After 25 weeks of age, systolic blood pressure in the low sodium group was 2.1 mm Hg lower (p < 0.01) than the normal sodium group. A 15-year follow-up of these children revealed that adjusted systolic and diastolic blood pressures were 3.6 mm Hg and 2.2 mm Hg lower, respectively, in children who had been assigned the low sodium diet during infancy (Geleijnse et al., 1997).
Although not frequently seen, hypernatremic dehydration has been reported in exclusively breast-fed infants (Kini et al., 1995; LSRO, 1998; Peters, 1989; Sofer et al., 1993). Sodium concentrations of the human milk consumed by some of these infants with hypernatremic dehydration ranged from 0.71 to 2.1 g (31 to 92 mmol)/L, which is significantly above the estimated typical content of human milk (0.13 to 0.16 g [5.6 to 7.0 mmol]/L) (see Table 6-8) (Kini et al., 1995; LSRO, 1998).
For infants, a UL could not be established because of insufficient data documenting the adverse effects of chronic intakes of overconsumption of sodium in this age group. To prevent high levels of sodium chloride intake, the only source of intake for infants should be human milk (or formula) and food to which as little sodium as possible is added during processing. Although evidence is limited, the potential long-term effects of reduced sodium formulas on blood pressure measured 15 years later (Geleijnse et al., 1997) suggest persistent adverse effects. Hence, as with other nu-