BACKGROUND: High serum sodium (sNa) concentrations may be associated with hypertension, which deteriorates kidney function. However, it is equivocal whether high sNa concentrations are associated with impaired kidney function independently of blood pressure (BP) or serum chloride (sCl). Therefore, we addressed this issue in an apparently healthy population.
METHODS: Clinical variables including estimated glomerular filtration rate (eGFR) were examined in 3603 men and women (aged 25-75 years) who underwent health-screening check-ups. sNa concentrations were classified into five categories.
RESULTS: Most parameters, including age and BP, increased with increasing sNa, whereas eGFR decreased. Logistic regression analysis showed that, compared with low-normal sNa (≤ 140 mEq/l), high sNa (≥ 144 mEq/l) was significantly associated with elevated BP (≥ 130/85 mmHg) even after adjustment for blood hematocrit, eGFR, serum potassium (sK) concentration and sCl. The highest sNa category was significantly associated with reduced eGFR (< 60 ml/min/1.73 m(2)) independently of elevated BP. Unlike adjustment for sK, adjustment for sCl strengthened the association between high sNa and elevated BP but attenuated the association between high sNa and reduced eGFR.
CONCLUSIONS: These results suggest that high sNa concentrations, even within the normal range, are independently associated with elevated BP and impaired kidney function. These associations may be substantially modified by sCl.
