The association between serum sodium concentration, hypertension and primary cardiovascular events: a retrospective cohort study

Abstract

The mechanisms underlying the adverse cardiovascular effects of increased salt intake are incompletely understood, but parallel increases in serum sodium concentration may be of importance. The aim of this retrospective cohort study was to investigate the relationship between serum sodium, hypertension and incident cardiovascular disease (CVD). Routinely collected primary care data from the Royal College of General Practitioners Research and Surveillance Centre were analysed. A total of 231,545 individuals with a measurement of serum sodium concentration at baseline were included. Exclusion criteria were: age < 40 years; abnormal serum sodium; diabetes mellitus; prior CVD event; stage 5 chronic kidney disease; and liver cirrhosis. The primary outcome was incident CVD (myocardial infarction, acute coronary syndrome, coronary revascularisation, stroke, transient ischaemic attack or new heart failure diagnosis) over 5 years. There was a ‘J-shaped’ relationship between serum sodium concentration and primary cardiovascular events that was independent of established risk factors, medications and other serum electrolytes. The lowest cardiovascular risk was found with a serum sodium between 141 and 143 mmol/l. Higher serum sodium was associated with increased risk in hypertensive individuals, whereas lower concentrations were associated with increased risk in all individuals. Therefore, alterations in serum sodium concentration may be a useful indicator of CVD risk. Higher serum sodium could have a direct effect on the vasculature, particularly in hypertensive individuals. Lower serum sodium may be a reflection of complex volume and neuroendocrine changes.

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Acknowledgements

Patients and practices of the RCGP Research and Surveillance Centre who allow their data to be used for surveillance and research; EMIS, InPractice Computer Systems, TPP SystmOne and other computerised medical record system vendors; Apollo Medical Systems who facilitate data extraction; and Barbara Arrowsmith, SQL Developer, for support with data extraction.

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Correspondence to Nicholas I. Cole.

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Conflict of interest

FJH is a member of Consensus Action on Salt & Health (CASH) and World Action on Salt & Health (WASH). Both CASH and WASH are non-profit charitable organisations and FJH does not receive any financial support from CASH or WASH. GAM is Chairman of Blood Pressure UK (BPUK), Chairman of CASH, WASH and Action on Sugar (AoS). BPUK, CASH, WASH and AoS are non-profit charitable organisations. GAM does not receive any financial support from any of these organisations. SdeL is Director of the RCGP RSC. The remaining authors declare that they have no conflict of interest.

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Cole, N.I., Suckling, R.J., Swift, P.A. et al. The association between serum sodium concentration, hypertension and primary cardiovascular events: a retrospective cohort study. J Hum Hypertens 33, 69–77 (2019). https://doi.org/10.1038/s41371-018-0115-5

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