Elevated Breast Milk Sodium and Seasonal Variation in Neonatal Hypernatremic Dehydration: A Descriptive Study from Northern Tunisia

Abstract

Background: Neonatal hypernatremic dehydration (NHD) is an underrecognized and a potentially serious condition, particularly in exclusively breastfed infants. Frequently overlooked in the early postnatal period, it may cause severe complications. While postnatal weight loss is a known indicator, the specific role of breast milk composition and environmental factors remains understudied. This study describes the clinical features, contributing factors, management, and outcomes of newborns diagnosed with NHD in a neonatal unit in northern Tunisia. Methods: We performed a retrospective descriptive study including all neonates admitted for NHD to the neonatal unit of Habib Bougatfa Hospital (Bizerte, Tunisia) between January 2022 and December 2025. Hypernatremia was defined as serum sodium >145 mmol/L and classified as moderate (150–159 mmol/L) or severe (>160 mmol/L). Demographic, clinical, laboratory data, management, breast milk sodium levels and outcomes were analyzed. Results: Thirty-two neonates were included (sex ratio 1.13), with a mean age of 3.85 ± 1.88 days at admission. Most infants (84%) were exclusively breastfed. A striking seasonal clustering was observed, with all cases admitted between May and October. The mean weight loss was 13.5%, and fever was the predominant symptom. The mean serum sodium level was 150.8 ± 4 mmol/L (50% had moderate hypernatremia and 3% severe hypernatremia). The mean breast milk sodium concentration performed in 24 mothers was elevated at 59.3 ± 20.5 mmol/L (normal <7 mmol/L). Functional renal impairment was common (78.1%). All infants recovered fully with controlled fluid correction without neurological sequelae or mortality. Conclusion: NHD is preventable and primarily affects exclusively breastfed infants, especially during warm periods. Early recognition of feeding difficulties, monitoring of postnatal weight loss, and controlled correction of sodium imbalance are crucial. Enhanced breastfeeding support and maternal education are essential to prevent this condition while promoting safe exclusive breastfeeding.