Reducing salt intake can lower the long-term risk of cardiovascular events: TOHP follow-up

April 23, 2007

Boston, MA - Cutting back on salt, while known to lower blood pressure, also appears to significantly reduce the long-term risk of cardiovascular events[1]. Observational follow-up from the Trials of Hypertension Prevention (TOHP) showed that a reduction in salt intake could reduce the risk of cardiovascular disease outcomes by 25%.

"The TOHP interventions reduced sodium intake by about 25% to 30%, approaching current recommendations for a 50% decrease in the amount of sodium in food in the United States," write Dr Nancy Cook (Brigham and Women's Hospital, Boston, MA) and colleagues in a report published online April 19, 2007 in the BMJ. "The observed reduction in cardiovascular risk associated with this sodium decrease was substantial and provides strong support for populationwide reduction in dietary sodium intake to prevent cardiovascular disease."

Reducing events, not risk factors

To date, long-term clinical trials evaluating the efficacy of sodium reduction on clinical events have not been conducted because of logistical and feasibility concerns, and previous population-based studies evaluating hard clinical end points have been limited and inconclusive, the authors note.

In this analysis investigators followed up on participants in two randomized lifestyle-intervention trials—TOHP I and TOHP II—for subsequent cardiovascular outcomes 10 to 15 years after the completion of these studies. Both of these trials, which included 744 subjects in TOHP I and 2382 subjects in TOHP II, found small but significant effects of sodium reduction on reducing blood pressure in normal-weight and overweight adults aged 30 to 54 years with high-normal blood pressure. Net sodium reductions in the intervention groups were 44 mmol/24 h and 33 mmol/24 h, respectively, or approximately 25% to 30%.

The relative risk of a cardiovascular event, defined as MI, stroke, revascularization, or cardiovascular death, was 25% lower among those randomized to the sodium-reduction intervention arm. When further adjusted for baseline sodium excretion and weight, as well as age, race, sex, trial, and clinic, the risk of a cardiovascular event was 30% lower in the intervention arm. Although there were trends for reductions in total mortality, these results did not achieve statistical significance.

Relative risk of cardiovascular disease overall, in TOHP I, and TOHP II

Group Salt intervention (%) Control (%) Hazard ratio (95% CI)
CVD*, overall 7.5 9.0 0.75 (0.57-0.99)
CVD, TOHP I 7.4 10.3 0.48 (0.25-0.92)
CVD, TOHP II 7.6 8.6 0.79 (0.57-1.09)
*Cardiovascular disease is a composite of MI, stroke, revascularization, or death due to cardiovascular causes

While the size and duration of the study are one of the strengths of the analysis, the investigators acknowledge that they achieved less-than-complete follow-up, obtaining information from 77% of study participants. In addition, the authors note that there were no direct measurements of blood pressure, weight, and sodium intake during follow-up, and they have only questionnaire data to support the long-term effects of the intervention.

Still, despite these drawbacks, Cook and colleagues conclude that the results of the TOHP follow-up "reinforce recommendations to lower dietary sodium intake as a means of preventing cardiovascular disease in the general population" and should alleviate residual concerns that sodium reduction might be harmful.

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