Benefits of Salt Restriction for Cardiovascular Disease Prevention and Treatment Questioned

DynaMed Weekly Update - Volume 6, Issue 31

Observational data have long suggested that higher dietary salt intake is associated with increased risk of cardiovascular disease (JAMA 1999 Dec 1;282(21):2027, BMJ 2009 Nov 24;339:b4567, Arch Intern Med 2011 Jul 11;171(13):1183). Results from randomized trials on the effects of restricting salt intake have been less consistent, and the clinical benefits of reduced sodium remain unclear. A recent Cochrane review examined 7 randomized trials evaluating interventions to reduce dietary salt intake (including either active salt restriction or advice to reduce salt use) in 6,489 adults, the largest collection of data to date. Trial durations ranged from 7-36 months, and the longest follow-up was 12.7 years.

In normotensive adults, reduced dietary salt was associated with a trend toward reduced all-cause mortality at trial end (up to 3 years) (relative risk [RR] 0.67, 95% CI 0.4-1.12), but not at longest follow-up (up to 12.7 years) in an analysis of 3 trials with 3,518 participants. Additionally, no significant differences in cardiovascular morbidity were found in an analysis of 2 trials with 2,505 participants at longest follow-up. Salt restriction significantly reduced diastolic blood pressure and trended toward reduced systolic pressure.

In trials with hypertensive adults, reduced dietary salt was associated with a trend toward reduced cardiovascular mortality at trial end in an analysis of 2 trials with 2,058 patients (RR 0.69, 95% CI 0.45-1.05). However, there were no significant differences in all-cause mortality at any time point or in cardiovascular morbidity at longest follow-up in this population. Salt restriction significantly reduced systolic but not diastolic blood pressure.

One trial compared low sodium vs. standard diets for 6 months in 232 patients with heart failure. In this population, reduced salt was associated with increased all-cause mortality (13.2% vs. 5.1%, p = 0.041, NNH 12).

Despite the large numbers of patients analyzed, there remains insufficient statistical power to confidently exclude the possibility of benefit from salt restriction for cardiovascular health (level 2 [mid-level] evidence) (Cochrane Database Syst Rev 2011 Jul 6;(7):CD009217).

For more information, see the Dietary recommendations for cardiovascular disease prevention topic in DynaMed.