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American Physiological Society

January 19, 2007

(BETHESDA, MD) — A new study concludes that low birthweight babies born with low sodium (salt) in their blood serum will likely consume large quantities of dietary sodium later in life. In the study, researchers also found that newborns with the most severe cases of low sodium blood serum consumed ~1700 mg more sodium per day and weighed some 30 percent more than their peers. These data, taken together with other recent findings, make it clear that very low serum sodium in pre-term and new born infants is a consistent and significant contributing factor for long-term sodium intake, a key marker for obesity.

The results are from the study "Lowest Neonatal Serum Sodium Predicts Sodium Intake in Low-Birthweight Children," conducted by Adi Shirazki, Edith Gershon, and Micah Leshem, all of the University of Haifa, Haifa; Zalman Weintraub of the Galilee Medical Center, Nahariya; and Dan Reich of the Ha'Emek Medical Center, Afula, Israel. The study is published in the American Journal of Physiology - Regulatory, Integrative, and Comparative Physiology. The Journal is one of 11 peer-reviewed research journals published each month by the American Physiological Society (APS) (www.The-APS.org).

The Study: Methodology
Forty-one children born prematurely and identified through the archives of the Ha'Emek and Galilee Medical Centers (Israel) participated in the investigation with the written permission of their guardians. The youngsters were admitted to the study based on whether they had received neonatal diuretic treatment during their first month of life (n=23) or were a matched control having received no diuretic treatment (n=18). Of the total, 21 were Arabs (14 boys, 7 girls) and 20 were Jews (11 boys, 9 girls), ranging between 8-15 years of age.

The researchers analyzed each child's sodium appetite according to neonatal diuretic treatment, and used each child's lowest recorded serum sodium levels as an index of sodium loss. The latter was determined by screening all the serum sodium measurements of each infant's postnatal medical record, and selecting the lowest.

Each child underwent a pediatric physical examination. To estimate current sodium appetite, participants were tested for their preferred concentration of salt in soup and sugar in tea, followed by orally administered spray tests involving table salt and table sugar. Between the tests the children and escorting parent(s) were interviewed about dietary and seasoning preferences. The children were then invited to eat freely from a table of salty and sweet snacks.

The researchers used trained experts to collect the above data. The investigators used ANOVA, correlational analysis (Spearman), and SPSS to analyze the data. Alpha was fixed at 0.05 and SEM was the measure of variability.

The Study: Results
Upon review of the data, the researchers concluded that:

- reported dietary sodium consumption in childhood (ages 8-15) was predicted by neonatal lowest serum sodium (NLS) and not by neonatal diuretic treatment, as they originally proposed.

- NLS predicted dietary sodium intake in both ethnic groups and both boys and girls.

- the 14 children with the most severe NLS (serum sodium<130 mEq/L) ate double the number of salty snacks (p<0.05) and their dietary sodium intake was substantially higher — 4515 ±310 mg/day vs. 3307± 248 (p=0.0054) — than their peers.

- no relationship was found between neonatal lowest serum sodium and a preference for salt per se. Rather, the preference was for the foods that contain it.

- gestational age and birthweight were not predictors of childhood sodium intake.

Conclusions
The researchers concluded that low sodium blood serum in infants - not gestational age, birthweight or neonatal diuretic treatment - predicts an increased intake of dietary sodium later in life. As neonatal serum sodium is a marker of future sodium intake, clinicians may wish to advise families of these children about the increased risk of sodium intake and obesity later in life.

American Physiological Society