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consumption beyond need must necessarily provide some kind of strong reward. People generally do not become highly attracted to substances unless these substances have powerful positive physiological effects. Greater understanding of the basis for high salt preference would help guide efforts to reduce that preference. Thus, there is a need to examine the existing knowledge about the origin of preference during human development.

EARLY DEVELOPMENT OF HUMAN SALT TASTE

Although human infants need sodium in moderation (IOM, 2005), at birth, they are indifferent to salt or reject it, particularly at concentrations higher than found in human blood (hypertonic). By approximately 4–6 months of age, infants show a preference (relative to plain water) for saline solutions around the level found in blood (isotonic) or even higher (Cowart et al., 2004). This age-related hedonic shift may represent in part the maturation of the salt taste receptor cell. Some rodent studies have shown that the ability to detect salt taste matures after birth (Hill and Mistretta, 1990); this may also be the case for humans.

The amount of salt an infant consumes can influence the infant’s salt taste preference (Harris and Booth, 1985). In a study by Geleijnse et al. (1997) it was reported that children who had been randomized to either a low or normal sodium diet during the first 6 months of life exhibited differences in blood pressure when tested after 15 years of follow-up, with the low sodium group having lower blood pressures. These data are consistent with the hypothesis that lowered exposure to salt in infancy results in lower preference and intake later in life. Unfortunately data were not collected to specifically test this hypothesis.

The most dramatic effects of early environmental variation on later salt preference and intake have been observed following large sodium loss (true sodium depletion, which is very rare in adulthood) during late fetal life or early infancy. Clinical observations (Beauchamp, 1991) and studies of clinical populations (Leshem, 2009) indicate that true sodium depletion during this period may enhance later salt liking, perhaps permanently. These human studies are consistent with a large body of experimental rodent studies indicating that early depletion causes permanent changes in neural circuits that mediate salt intake. Since there is very little evidence that adult salt depletion has comparable long-term effects on salt liking (Beauchamp et al., 1990; Leshem, 2009), one may speculate that variation in salt exposure during a critical period of maturation permanently alters peripheral or central structures or both and is thereby particularly potent in establishing childhood and perhaps even adult patterns of sodium intake.

Children have been reported to have higher preference for salt than do adults (Beauchamp and Cowart, 1990; Beauchamp et al., 1990; Desor



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