Cardiology Update: High Sodium bad, low sodium worse

CV events more with more sodium in hypertension also more with low sodium in non hypertensive

Sodium has been traditionally associated with hypertension and with more cardio vascular mortality. Restriction of sodium has been recommended as the treatment of hypertension as well as prevention of hypertension

Several recent studies in a variety of different populations have reported a U-shaped association between sodium consumption and cardiovascular disease and mortality, with increased risk at both high and low sodium intakes.

Whether these associations vary between those individuals with and without hypertension is uncertain. Mente et al conducted a pooled analysis of a large sample of individuals with and without hypertension to better define the association between sodium intake and cardiovascular disease events and all cause mortality according to hypertension status.

The researchers studied data from 4 international prospective studies on 133,118 individuals (63,559 with hypertension and 69,559 without hypertension) from 49 countries. Mean estimated 24-h urinary sodium excretion values were computed overall (as group-level measure of intake) and according to hypertension status.

Mean age was 54.4 years overall, 58.6 years in individuals with hypertension and 50.5 years in those without hypertension. Almost three quarters (74%) were without previous cardiovascular disease and 89% were without diabetes. Mean estimated sodium excretion was 4956 mg/day in those with hypertension and 4823 mg/day in those without hypertension.

Over a median follow-up of 4.2 years, increased sodium intake was associated with greater increases in systolic blood pressure in individuals with hypertension (2.08 mm Hg change per g sodium increase) compared with individuals without hypertension (1.22 mm Hg change per g; p for interaction <0.0001).

The primary composite outcome of death and major cardiovascular disease events occurred in 6835 individuals with hypertension (11%) and in 3021 of those without (4%). Participants with 4-5 g/day of sodium excretion had the lowest risk and this was used as the reference category.

In patients with hypertension, sodium excretion of ≥7 g/day or less than 3 g/day both had increased risk for the primary outcome compared to those with sodium excretion in the 4 to 5-g/day reference range (hazard ratios [HR], 1.23 and 1.34, respectively; p<0.0001 for both comparisons).

However, a different pattern was noted for participants without hypertension: Compared to individuals with sodium excretion within the reference range, higher sodium excretion was not associated with increased risk of the primary outcome (HR, 0.90; p=0.2547), but sodium excretion of <3 g/day was associated with a significantly increased risk (HR 1.26; p=0.0009).

The investigators concluded that based on this large diverse sample, compared with moderate sodium intake, low sodium intake is associated with increased risk of death and cardiovascular disease in hypertensive and nor motensive individuals. High sodium intake, on the other hand, is only associated with an increased risk of adverse cardiovascular events and death in hypertensive individuals. The authors suggested that their data indicate that efforts to lower sodium intake might be best targeted to populations with hypertension who consume high sodium diets.

Reference

• 1Mente A, O’Donnell M, Rangarajan S, et al.Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies.Lancet. 2016; 388: 465-75.