Blog entry by Meguid El Nahas
Two articles have been published this month in the NEJM relating to the PURE study outcomes:
N Engl J Med. 2014 Aug 14;371(7):601-11. doi: 10.1056/NEJMoa1311989.
N Engl J Med. 2014 Aug 14;371(7):612-23. doi: 10.1056/NEJMoa1311889.
The FIRST PUBLICATION, showed that a high urinary excretion of sodium correlates, in a large population (>100,000) in 18 countries worldwide, with systolic and diastolic blood pressure (BP). The slope of the association was steeper for those with hypertension and in older age (>55 years).
An inverse relationship was noted with high urinary potassium excretion.
SO FAR SO GOOD, SO A HIGH URINARY SODIUM EXCRETION = A HIGH SODIUM INTAKE IS ASSOCIATED IN THOSE AT HIGHER RISK WITH A RISE IN BP. THIS ALL THE WAY AS FAR AS SODIUM EXCRETION TO <3G/DAY.
THE SECOND PUBLICATION, showed that a urinary sodium excretion/intake of <3g and >6g/day is associated with increased CARDIOVASCULAR EVENTS. In this study, low <3g/day and high >6g/day sodium intake was associated with increased CVD events. Those individuals between 3 and 6g/day of sodium intake had the lowest CVD. Thus defining a U shape curve with increased risk at high and low sodium intake levels.
In fact, such J/U shaped curve also goes along a similar curve profile for BP and in that respect does not contradict the first study; low BP like High BP are associated with increased mortality. High BP leads to increased risk of CVD and low may reflect the presence of severe CVD and heart failure, specially in the elderly.
Similarly, high sodium/salt intake is associated with high BP and increased CVD whilst low sodium intake may reflect poor health, poor food intake also reflecting an underlying higher comorbidity.
SO WHERE'S THE CONFUSION?
The confusion emanates from such observations (implying that a low sodium/salt intake may be potentially harmful) and current BP guidelines and recommendations including those for CKD patients that advise to reduce the sodium intake of patients to <2g/day:
Thus leaving us in a confused state:
Is lower sodium intake beneficial?
Is lower sodium intake harmful?
Is lower sodium intake beneficial in some age group; >55 years and/or hypertensive?
Is lower sodium intake harmful/unncessary in some age groups <55years and/or normotensive?
Which brings us back to guidelines and healthcare management in general that has to be tailored and adjusted to the individual under consideration as data derived from cross sectional observational studeis like PURE are at best hypothesis generating and not convincing facts we can build our practice upon.
So perhaps we would only be confused if we surrender our own common sense and judgement and apply guidelines an drecommendations blindly...
ONE SIZE NEVER FITS ALL IN MEDICINE...THIS IS HIGHLIGHTED IN REGARDS TO SODIUM INTAKE AS WELL AS BLOOD PRESSURE LEVELS AND CONTROL.
AGE AND COMORBIDITIES HAVE TO BE TAKEN INTO CONSIDERATION WHEN WE MAKE OUR OWN CLINICAL DECISIONS....MORE SALT IN SOME...LESS SALT IN OTHERS...PURE-LY CONVINCING!