Does low sodium increase cardiovascular disease risk?

In individuals with or without hypertension, low urinary sodium excretion is associated with an increased risk of death and cardiovascular death, according to a controversial meta-analysis published in The Lancet

The researchers analyzed pooled data on more than 133,000 individuals from 49 countries drawn from four large prospective studies. About 64,000 participants were classified as having hypertension defined as untreated BP of 140/90 mm Hg or greater or prescribed antihypertensive medications at baseline. The relationship between estimated 24-hour urinary sodium excretion and a composite outcome of death and major cardiovascular disease events was assessed for the groups with versus without hypertension.

At a median 4.2 years of follow-up, there were 6835 events in individuals with hypertension and 3021 in those without hypertension. Per gram of increased sodium, systolic BP increased by 2.08 mm Hg in the hypertensive group versus 1.22 mm Hg in the nonhypertensive group. In the hypertensive group, risk of death or cardiovascular events was increased at sodium excretion of 7 g/d or greater and at less than 3 g/d (hazard ratios of 1.23 and 1.34, respectively).

In individuals without hypertension, higher sodium excretion was not significantly associated with risk of death or cardiovascular disease events. However, risk was elevated for nonhypertensive subjects with sodium excretion of less than 3 g/d (hazard ratio of 1.26). In both groups, 11 percent of participants had sodium excretion less than 3 g/d.

The results suggest that, in individuals with hypertension, both high and low sodium intakes are associated with an increased risk of cardiovascular disease and death. Among those without hypertension, risk is increased only for those with low sodium intake. The investigators conclude that “[t]hese data suggest that lowering sodium intake is best targeted at populations with hypertension who consume high sodium diets” [Mente A, 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, DOI: http://dx.doi.org/10.1016/S0140-6736(16)30467-6].