Background

The goal of this systematic review was to determine whether sodium intake is associated with risk of cardiovascular disease (CVD). In order to answer this question, the 2015 Dietary Guidelines Advisory Committee (DGAC) updated systematic reviews done on this topic by the Institute of Medicine (IOM) and the National Heart, Lung, and Blood Institute (NHLBI) in 2013.

Conclusion statement

The DGAC concurs with the IOM review, which concluded that “although the reviewed evidence on associations between sodium intake and direct health outcomes has methodological flaws and limitations, when considered collectively, it indicates a positive relationship between higher levels of sodium intake and risk of CVD. This evidence is consistent with existing evidence on blood pressure as a surrogate indicator of CVD risk.”

IOM Grade: Grade not determined, outside the statement of task

2015 DGAC Grade: Moderate

The DGAC concurs with the IOM conclusion that “evidence from studies on direct health outcomes is inconsistent and insufficient to conclude that lowering sodium intakes below 2,300mg per day either increases or decreases risk of CVD outcomes (including stroke and CVD mortality) or all-cause mortality in the general US population.”

IOM Grade: Grade not determined, outside the statement of task

2015 DGAC Grade: Not Assignable

The DGAC concurs with the NHLBI review, which concluded that “a reduction in sodium intake by approximately 1,000mg per day reduces CVD events by about 30%” and that “higher dietary sodium intake is associated with a greater risk for fatal and nonfatal stroke and CVD.”

NHLBI Strength of Evidence: Low

2015 DGAC Grade: Limited

The DGAC concurs with the NHLBI conclusion that “evidence is not sufficient to determine the association between sodium intake and the development of heart failure.”

NHLBI Strength of Evidence: Not assigned due to insufficient evidence

2015 DGAC Grade: Not Assignable

Methods

To update the 2013 IOM and NHLBI systematic reviews on this topic, literature searches were conducted using PubMed, Embase, Navigator (BIOSIS, CAB Abstracts and Food Science and Technology Abstracts) and Cochrane databases to identify studies that evaluated the association between sodium and cardiovascular disease. Studies that met the following criteria were included in the review: randomized controlled trials (RCTs), non-randomized controlled trials or prospective cohort studies; human subjects who were healthy or at elevated chronic disease risk; subjects from countries with high or very high human development (2012 Human Development Index) (if a study included subjects from multiple countries with differing Human Development Index ratings, the study was included); and published in English in peer-reviewed journals. The date range was from January 2013 to September 2014. The intervention or exposure was sodium intake, and the outcome was myocardial infarction (MI), stroke, coronary heart disease (CHD), CVD-related mortality, incidence of hypertension and congestive heart failure.

Data from each included article were extracted, and risk of bias was assessed. The evidence was qualitatively synthesized, a conclusion statement was developed and the strength of the evidence (grade) was assessed using pre-established criteria including evaluation of the quality and risk of bias, quantity, consistency, magnitude of effect and generalizability of available evidence. The 2015 DGAC then considered the studies published since 2010 on sodium and cardiovascular, and determined whether the conclusions reached by the IOM and NHLBI needed to be modified.

Findings

• The DGAC updated systematic reviews done in 2013 by the IOM and NHLBI, and identified four additional articles published since 2013, all of which were prospective cohort studies
• The evidence reviewed for the 2013 IOM report was published between 2003 and December 2012
• The DGAC considered the conclusions reached by the IOM and NHLBI related to dietary sodium intake and risk of CVD, and determined that the findings from the four new studies identified in the updated search did not warrant changes to the conclusion statements. In aggregate, the data indicate a relationship between higher sodium intake and higher risk of CVD.

Limitations

The ability to draw strong conclusions was limited by the following issues:

• A small number of well-conducted studies evaluating sodium intake and direct health outcomes
• Inconsistency in findings across the published literature, possibly due to methodological factors
• Lack of comparability in sodium intake levels across studies, particularity in international studies
• Absence of strong data related to sodium goals and direct health outcomes, not including hypertension.