Dietary salt-reduction benefits remain unproven
There is not enough evidence to prove that reducing dietary salt intake results in statistically significant reductions in overall mortality or cardiovascular morbidity, data from a systemic review of clinical trials that involved 6,500 participants indicated.
“Cutting down on the amount of salt has no clear benefits in terms of likelihood of dying or experiencing cardiovascular disease,” Rod S. Taylor, PhD, of the Peninsula College of Medicine and Dentistry in Exeter, England, and colleagues wrote in a report published in the Cochrane Database of Systemic Reviews.
Furthermore, the researchers observed increased mortality risk among patients with congestive heart failure who restricted salt, suggesting that more randomized clinical trials are needed to determine whether these dietary recommendations may actually be harmful for some people.
“With governments setting ever lower targets for salt intake and food manufacturers working to remove it from their products, it's really important that we do some large research trials to get a full understanding of the benefits and risks of reducing salt intake,” Taylor said in a press release.
Evidence supporting low sodium diets to promote cardiovascular health is based on the relationship between salt intake and BP, with research indicating that BP reduction of 2mm to 3 mm Hg are necessary to achieve clinically significant results, according to background information in the report.
However, data from a previous Cochrane review showed that intensive salt-reduction strategies resulted in only modest BP reductions, averaging 1.1/0.6 mm Hg. This earlier review was based on small numbers of clinical events and death, so Taylor et al set out to confirm whether salt-reduction actually reduce cardiovascular morbidity and mortality with a larger, updated analysis.
The researchers reviewed seven studies that included 3,518 normotensive participants, 758 hypertensive participants, 1,981 participants that were either normotensive or hypertensive, and 232 patients with heart failure. Follow-up ranged from seven to 36 months, with the longest at 12.7 years.
Analyses revealed the following:
- Among normotensive individuals, salt restriction reduced the risk of death 33% during the trial, but this waned to 10% during the follow-up period. These outcomes were not statistically significant due to overlapping confidence intervals.
- Among hypertensive participants salt restriction reduced mortality by 3% at trial end and 4% after the follow-up period.
- Reducing salt intake reduced cardiovascular events by 29% among normotensive participants and 16% among hypertensive participants; however, neither difference was statistically significant.
- Salt restriction increased mortality risk more than two-fold among patients with heart failure compared with a control group (RR= 2.59; 95% CI: 1.04-6.44).
“Intensive support and encouragement to reduce salt intake did lead to a reduction in salt eaten and a small reduction in BP after more than six months,” the researchers wrote. “[But] there was not enough information to understand the effect of these changes in salt intake on deaths or cardiovascular disease.”
The American Heart Association continues to recommend limiting daily salt intake to 1,500 mg, and issued a statement pointing out the limitations of the studies included in the analyses, including low representation of blacks and elderly populations — two groups at increased risk for hypertension. The AHA also questioned the adequacy of follow-up duration in the studies included, as well as the use of food diaries instead of urinary excretion to measure sodium intake.
“Nine out of 10 Americans will develop high blood pressure in their lifetime," AHA officials said in the statement. "Reducing sodium now — even for people who currently have normal blood pressure — can reap enormous long-term benefits by reducing the risk for developing high blood pressure and helping those with high blood pressure manage their condition more effectively."