Patients with CKD are known to be at an increased risk of CVD compared with the general population.
The outcomes of this study, which feature in the JAMA journal, attempt to clarify the association between sodium intake and CVD, which have produced contradictory research results.
According to the European Renal Association, 10% of the population in Europe are affected by CKD. Around 70 million Europeans have lost some of their kidney function and are at high risk of becoming dependent on dialysis or transplantation.
The study, which took place at the Tulane University School of Public Health and Tropical Medicine, New Orleans, found a significantly increased risk of CVD in individuals with the highest urinary sodium excretion.
This main conclusion was confirmed even when several CVD risk factors were taken into consideration including the use of antihypertensive medications and history of CVD.
This study enrolled 3,757 CKD patients into the Chronic Renal Insufficiency Cohort (CRIC) Study. These patients were followed up from May 2003 to March 2013.
Subjects were asked to provide urine samples at the start of the study and the first 2 annual follow-up visits.
Among the participants, who had an average age of 58 years and were 45% women, 804 CVD events (congestive heart failure, stroke, or heart attack) occurred during a median 6.8 years of follow-up.
The total incidence of CVD events in the highest quartile of calibrated sodium excretion compared with the lowest was 23.2% versus 13.3% for heart failure, 10.9% versus 7.8% for heart attack and 6.4% versus 2.7% for stroke.
Put simply, the higher the sodium concentrations in urine excreted by CKD patients the higher the risk of a CVD event.
“The findings in this analysis as a whole support a positive association between urinary sodium excretion and CVD, which is particularly strong in individuals with the highest urinary sodium excretion," the study noted.
Blood pressure of patients with CKD is more sensitive to high sodium intake than persons with normal kidney function due to a diminished capacity to excrete sodium.
Study limitations mentioned included inconsistencies in dietary sodium measurement methods, which could contribute to these conflicting findings.
Other mechanisms in play
The findings of this study were independent of adjustment for systolic blood pressure, suggesting other mechanisms might’ve played a role in the effect of dietary sodium on CVD in CKD patients.
This is consistent with previous findings of a positive association between dietary sodium and CVD independent of blood pressure.
Other possible mechanisms mentioned include endothelial dysfunction, increased oxidative stress leading to vascular damage, insulin resistance, and activity in the renin-angiotensin-aldosterone system activity.
In a statement by The Salt Association, the industry organisation said that the war on salt had continued for decades, without firm evidence of any long-term health benefits from restricted salt diets.
In particular, ‘sodium’s relationship to blood pressure is modulated by many dietary and non-dietary factors, including the interaction and balance of a range of essential minerals.’
Published online ahead of print, doi:10.1001/jama.2016.4447
“Sodium Excretion and the Risk of Cardiovascular Disease in Patients With Chronic Kidney Disease.”
Authors: Jiang He et al.