Risk of hypertension and heart failure linked to high-normal serum sodium and tonicity in general healthcare electronic medical records.

Aims: Population ageing is fuelling an epidemic of age-related chronic diseases. Managing risk factors and lifestyle interventions have proven effective in disease prevention. Recent epidemiological studies have suggested poor hydration as a modifiable risk factor, linked to a higher risk of chronic diseases. We evaluate whether hydration-related markers, serum sodium and tonicity, can serve as risk factors for hypertension and heart failure informing hydration-focused interventions in general health care.

Methods and results: We analysed 407 187 adults (18-104 years) from 20-year electronic medical records from Israel's Leumit Healthcare Services. We included individuals without significant chronic diseases and water balance issues, having normal serum sodium (135-146 mmol/L). Cox proportional hazards models were used to assess the risk of developing hypertension and heart failure. Our analysis showed an increased risk of hypertension with higher serum sodium levels: a 13% rise at 140-142 mmol/L and 29% for levels above 143 mmol/L [hazard ratio (HR) 1.29, 95% confidence interval (CI): 1.25-1.33]. Tonicity over 287 mosmol/kg was associated with a 19% increased risk of hypertension (HR 1.19, 95% CI: 1.17-1.22). The risk of heart failure also increased, reaching 20% for sodium above 143 mmol/L (HR 1.20, 95% CI: 1.12-1.29) and 15% for tonicity above 289 mosmol/kg (HR 1.16, 95% CI: 1.08-1.21). Among current healthy Leumit members, 19% had serum sodium within the 143-146 mmol/L range and 39% were in the 140-142 mmol/L range.

Conclusion: A serum sodium and tonicity exceeding 140 mmol/L and 287 mosmol/kg are associated with increased risk of hypertension and heart failure in the general Israeli population. These thresholds could be used to identify individuals at risk, warranting additional clinical evaluations and guiding preventive intervention.