THE INFLUENCE OF SODIUM ON GROWTH IN INFANCY

Sodium (Na) is an important growth factor, stimulating cell proliferat ion and protein synthesis and increasing cell mass. Sodium chloride (N aCl) deprivation inhibits growth, as reflected by reduced body and bra in weight, length, muscle and brain protein and RNA content and brain lipid content compared with controls. This is not due to deficiency of other nutrients since control and experimental diets were identical e xcept for NaCl content. Subsequent NaCl supplementation restores growt h velocity to control values but does not induce ''catch-up'' growth. In humans, salt loss causes growth failure and subsequent salt repleti on improves growth. Preterm infants <32 weeks' gestation at birth are renal salt losers in the first 2 weeks of post-natal Life and are vuln erable to hy ponatraemia. This can be prevented by increasing Na intak e, which also produces accelerated weight gain that persists beyond th e period of supplementation. Early nutrition in preterm infants can af fect subsequent growth and also cognitive function: this is probably m ultifactorial, but NaCl intake differed substantially between study gr oups and is likely to be an important factor. The mechanism whereby Na promotes cell growth is not understood, but stimulation of the membra ne Na+,H+-antiporter with alkalinization of the cell interior is a lik ely possibility.