Sodium intake was positively associated with cortisol excretion in a cross-sectional sample of Australian school children

Background: The detrimental effects on health of high sodium intake and chronically elevated cortisol levels are well known. There is also evidence in adults that high sodium intake is associated with high levels of urinary cortisol excretion (1). We aimed to assess in children if urinary excretion of sodium was related to urinary excretion of cortisol and cortisol metabolites. Methods: A cross-sectional sample of school children and their mothers who performed 24 hour urine collection in which sodium, potassium, free cortisol (enzyme-linked immunosorbent assay) and cortisol metabolites (gas chromatography-mass spectrometry) were measured. Results: School children (n=120; mean(±SD) age = 9.2±2.0 years) and their mothers (n=102; 41.7±5.1 years) participated. Sodium and potassium excretion was 104.2±61.8 (mean±SD) and 46.8±18.5 mmol/24h, respectively, in children and 120.0±41.3 and 67.6±18.5 mmol/24h, respectively, in mothers. Multiple regression analysis adjusting for age, sex and BMI z score indicated that children's urinary sodium excretion was positively associated (P<0.01) with urinary free cortisol (β=0.38 (0.13, 0.61; 95% CI)) and urinary cortisol metabolites (β=0.009 (0.004, 0.013)). Positive associations (P<0.001) were also observed between potassium excretion and urinary free cortisol (β=1.08 (0.53, 1.62)) and urinary cortisol metabolites (β=0.03 (0.01, 0.04)). There were no relationships between urinary electrolytes and cortisol excretion in mothers. Conclusions: Sodium and potassium intake was positively associated with urinary free cortisol and cortisol metabolites in children but not in mothers. Population salt reduction programs may have additional beneficial effects on reducing cortisol levels in children.