Blood Pressure and Sodium Intake: The Established Link

The link between dietary sodium intake and blood pressure has been established by numerous clinical studies over the last 30 years. The connection is strongest between excess sodium intake and hypertension, but decreasing sodium intake can also lower blood pressure in “high normal” or prehypertensive individuals.1

Several studies, including DASH-Sodium (Dietary Approaches to Stop Hypertension; identifier: NCT00000544), have demonstrated that reducing sodium intake to as low as <1.5 g/d lowered blood pressure to a modest degree.2,3 The findings from DASH-Sodium in particular have strongly influenced guidelines for blood pressure management. The American Heart Association (AHA) recommends maintaining sodium intake levels below 1.5 g/d to help prevent cardiovascular disease (CVD).2,3

However, it is unclear whether lowering blood pressure by reducing sodium intake improves CV outcomes and overall mortality. “There is much controversy regarding the effects of sodium on mortality, especially with lower sodium intake,” Nancy R. Cook, ScD, of Brigham and Women’s Hospital in Boston, said in an interview with Cardiology Advisor. “While decreasing sodium intake clearly improves blood pressure, not all studies have found a benefit for CVD or mortality.”

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To that point, excess sodium intake can raise the risk for CVD, but surprisingly, very low levels of sodium intake have also been associated with increased CVD and mortality. In contrast, a study that evaluated 10- to 15-year follow-up data from  TOHP (Trials of Hypertension Prevention; identifier: NCT00000528) demonstrated that the lowest levels of sodium intake correlated with the lowest CV risk.1

To investigate the relationship between sodium intake and total mortality, Dr Cook and colleagues examined long-term mortality data from phase 1 and phase 2 of TOHP (TOHP I and TOHP II). Their findings were recently published in the Journal of the American College of Cardiology.1

Long-Term Mortality in TOHP

In TOHP I, 744 participants were randomly assigned to active sodium reduction or usual care for 18 months.5 In TOHP II, 2382 participants were treated with sodium reduction, weight loss intervention, combined sodium plus weight loss intervention, or usual care for 36 to 48 months.6 Both studies found that urinary sodium excretion and blood pressure were significantly lower in the reduced-sodium groups compared with usual care.5,6

In the current trial, mortality data spanning 23 to 26 years after randomization were collected on TOHP participants. Mortality rates among patients treated with sodium reduction and usual care in TOHP I were 10.1% and 10.6%, respectively; in TOHP II, 6.9% and 7.7%, respectively. This translated into a 15% lower mortality risk, albeit nonsignificant, in patients receiving the reduced sodium intervention (hazard ratio [HR]: 0.85; 95% confidence interval [CI], 0.66-1.09; P =.19).1