Abstract and Introduction
Abstract
Effective population-based interventions are required to reduce the global burden of cardiovascular disease (CVD). Reducing salt intake has emerged as a leading target, with many guidelines recommending sodium intakes of 2.3 g/day or lower. These guideline thresholds are based largely on clinical trials reporting a reduction in blood pressure with low, compared with moderate, intake. However, no large-scale randomized trials have been conducted to determine the effect of low sodium intake on CV events. Prospective cohort studies evaluating the association between sodium intake and CV outcomes have been inconsistent and a number of recent studies have reported an association between low sodium intake (in the range recommended by current guidelines) and an increased risk of CV death. In the largest of these studies, a J-shaped association between sodium intake and CV death and heart failure was found. Despite a large body of research in this area, there are divergent interpretations of these data, with some advocating a re-evaluation of the current guideline recommendations. In this article, we explore potential reasons for the differing interpretations of existing evidence on the association between sodium intake and CVD. Similar to other areas in prevention, the controversy is likely to remain unresolved until large-scale definitive randomized controlled trials are conducted to determine the effect of low sodium intake (compared to moderate intake) on CVD incidence.
Introduction
Population-based interventions to reduce the risk of cardiovascular disease (CVD) should target a common risk factor, which is modifiable through simple effective interventions and may be implemented in a range of settings and populations. Reducing excess sodium intake presents a compelling target for population-based prevention of CVD, given its association with blood pressure and that interventions to reduce sodium intake may be targeted at individual, community, societal, and policy levels.
In 2003, the World Heart Organization (WHO) recommended that adults ingest <2.0 g/day of sodium (which corresponds to 5 g of salt/day), based on an assessment of the best available evidence. At that time, some epidemiological studies reported an association between higher levels of sodium intake and CV events, and clinical trials had demonstrated that reduced sodium intake to low levels was associated with a reduction in blood pressure which formed the basis for guideline thresholds. Since then, however, there have been a number of studies that have questioned whether the recommended target of sodium intake is optimal, with some recent studies reporting that intakes of under 3 g/day may be associated with an increased risk of CV death. These recent studies, and the absence of a definitive randomized controlled trial indicating that reducing sodium intake to low levels will reduce CVD, have re-ignited the controversy surrounding the optimal target for sodium intake. Despite a large number of studies evaluating the association between sodium intake and blood pressure and CVD, there are few areas in CVD prevention that evoke more diverse opinions.
In this article, we explore potential reasons for the differing interpretations of existing evidence on the association between sodium intake and CVD, such as differences in methods of measurement, population characteristics, study designs, and outcome measures. In addition, reduction in sodium intake may have differing effects on other dietary factors known to affect CV risk, which may vary by population. We also contend that there may be a J-shaped association between sodium intake and CVD, which is the principal reason for different findings between studies. Finally, we present some approaches that are required to clarify the uncertainty, and discuss what further research is required to determine the optimal sodium intake range.