Point/Counterpoint
The Population Risks of Dietary Salt Excess Are Exaggerated

https://doi.org/10.1016/j.cjca.2014.02.003Get rights and content

Abstract

Policy positions on salt consumption (based largely on the association of sodium and blood pressure [BP]) has remained unchanged since the 1970s, until recently. However, this is beginning to change as new evidence emerges. The evidence supports a strong association of sodium with BP and cardiovascular disease events in hypertensive individuals, the elderly, and those who consume > 6 g/d of sodium. However, there is no association of sodium with clinical events at 3 to 6 g/day and a paradoxical higher rate of events at < 3 g/day. Therefore, until new evidence emerges, the optimal range of sodium consumption should be considered to be between 3 and 6 g/d. Population-wide sodium reduction is not justified in countries such as Canada.

Résumé

Les positions sur les politiques de consommation de sel (basées en grande partie sur le lien entre le sodium et la pression artérielle [PA]) sont demeurées inchangées depuis les années 70 jusqu'à tout récemment. Cependant, des changements s’amorcent étant donné que de nouvelles données scientifiques apparaissent. Les données soutiennent qu’il existe un lien important entre le sodium et la PA et les événements cardiovasculaires chez les individus hypertendus, les personnes âgées et les personnes qui consomment > 6 g/j de sodium. Cependant, on n'observe aucun lien entre le sodium et les événements cliniques à raison de 3 à 6 g/j, et l'incidence paradoxalement plus élevée d'événements à < 3 g/j. Par conséquent, jusqu’à ce que de nouvelles données scientifiques voient le jour, l’étendue optimale de la consommation de sodium devrait être située entre 3 et 6 g/j. La réduction de sodium à l’échelle de la population n’est pas justifiée dans des pays comme le Canada.

Section snippets

Sodium and BP: A Historical Overview

Dahl in the early 1960s showed that chronic excess salt ingestion led to sustained hypertension in rats who were fed extremely large amounts of salt.6 Only rats selectively bred to be “susceptible” to hypertensive responses to salt showed pronounced BP increases, whereas “resistant” rats did not.7 In 1970, a National Academy of Sciences committee concluded that the accumulated evidence incriminating salt as causing hypertension was inconclusive. Nevertheless, the food industry saw a market for

The Population Urban Rural Epidemiologic (PURE) Study

INTERSALT (with 10,000 individuals) was not large enough to assess the nature of the relationship (eg, whether the association is linear or nonlinear) between sodium and BP or the effects in key subpopulations (eg, hypertensive patients or different ethnic groups). To address these questions, a substantially larger study of sodium and BP would be needed.

Recently, new data were reported from the PURE study (presented at the European Society of Cardiology meeting in September 2013) on over

Is Sodium Reduction to Low Levels Feasible?

Some guidelines recommend reducing the sodium consumption of the general population to < 2.3 g/d, and some recommend reduction to even 1.5 g/d. Currently the average intake of sodium in Western populations is about 3.5-4.0 g of sodium per day. In the United States, only 9% of adults consume < 2.3 g/d, and just 0.6% consume < 1.5 g/d.17 In the PURE study of over 100,000 individuals globally,21 very few individuals consumed < 2300 mg of sodium, and practically none consumed < 1500 mg. This

Shortcomings of BP as a Surrogate to Predict Effects of Sodium Reduction on Clinical Outcomes

The contention that BP reductions, irrespective of the approach and the baseline level of BP, will translate into reduction of CVD reductions is not proved. For instance, recent trials showed that some agents reduce BP but have no effect on clinical outcomes,27 other agents reduce BP only modestly but produce a substantial reduction in CVD,28 and different agents reduce BP to similar extents and yet differ in their impact on CVD and individual CVD outcomes.29, 30 Further, even in high-risk

Shift in Focus From Surrogate Measures to Clinical Outcomes

In recent years, there has been a shift in focus from surrogate measures (eg, BP) to clinical outcomes (eg, MI, stroke, heart failure, CVD, and mortality).

Cohort studies

A 2009 meta-analysis of 13 prospective cohort studies that compared highest vs lowest quantiles of sodium intake among studies reported that a 2 g/d increase in sodium intake (5 g of salt) was associated with an increased risk of stroke (relative risk [RR], 1.23; 95% CI, 1.06-1.43) and composite of all CV events (RR, 1.14; 95% CI, 0.99-1.32).38 However, for both outcomes, there was significant heterogeneity across studies. Given the differing ranges of sodium intake of populations included in

Conclusions

The evidence supports a strong association between sodium and BP in individuals with hypertension, the elderly, and those who consume > 5-6 g/d of sodium. There is little impact on BP and clinical events at lower levels of consumption and concerns about harm at sodium intake < 3 g/d. Therefore, until new evidence (ideally from large RCTs) emerges, the optimal range of sodium consumption should be considered to be between 3 and 6 g/d. The vast majority of Canadians (94%) have sodium intakes < 6

Funding Sources

S.Y. holds the Heart and Stroke foundation/Marion W. Burke Chair in Cardiovascular Disease.

Disclosures

The authors have no conflicts of interest to disclose.

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