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Children born with low birth weight are at heightened risk for an exaggerated blood pressure response to dietary salt, in concert with reduced renal mass, Swiss researchers report in the August 11 early online issue of Hypertension.

Children born with low birth weight are at heightened risk for an exaggerated blood pressure response to dietary salt, in concert with reduced renal mass, Swiss researchers report in the August 11 early online issue of Hypertension.

In this study of children at ages seven to 15 year years, "salt sensitivity is not reflected in the baseline 24-hour ambulatory blood pressure monitoring, suggesting at least in part a functional response to salt at this age," the authors state.

Dr. Markus G. Mohaupt and colleagues at the University of Bern note that low birth weight (LBW) is associated with an increased incidence of cardiovascular disease, hypertension, diabetes, and kidney disease in adulthood.

To test their theory that evidence of renal impairment would be present during childhood, they studied 50 healthy white children, including 35 born at < 2500 g and 15 born at term with birthweight appropriate for gestational age (AGA).

In the LBW group, six children were diagnosed with white coat hypertension and two with sustained hypertension, and mean systolic office blood pressure was higher than in children born at term AGA. Although calculated glomerular filtration rate was within normal limits in all subjects, it was significantly lower in children with LBW.

To assess salt sensitivity, subjects maintained a regular diet omitting food high in sodium for seven days, followed by a regular diet enriched with salt tablets for 7 days.

Twenty-four LBW children were compliant with the study protocol. Nine subjects (37 per cent), including eight (47 per cent) who were born small for gestational age, were salt sensitive, defined as having higher mean arterial pressure during 24-hour ambulatory blood pressure monitoring when salt intake was increased.

The authors observed a negative linear correlation between the degree of salt sensitivity and kidney length and volume determined by ultrasound.

"These observations are evidence of the important role of early renal mass as an indicator of appropriate organ and functional development," the authors conclude.

They recommend dietary counseling to restrict dietary salt and continued health surveillance of children born with LBW.

Hypertension 2008;52