Recommendations on sodium intake for cardiovascular health: conviction or evidence?

This commentary refers to ‘2018 ESC/ESH Guidelines for the management of arterial hypertension’, by B. Williams et al., 2018;39:3021–3104. To the Editor, Leading health organizations worldwide have endorsed empirical thresholds for sodium intake as a basic tenet in cardiovascular prevention. Such recommendations are largely based on evidence suggesting an unfavourable blood pressure increase with high sodium intake.1 However, given the absence of randomized controlled trials, the effects of dietary sodium restriction on patient-relevant endpoints are not entirely clear. Observational evidence points to a J-shaped association between sodium intake and cardiovascular mortality in both the general population and patients with hypertension. In contrast, high dietary potassium intake is consistently associated with prognostic benefit.2 We recently brought to attention a transposition error in the 2018 ESC/ESH Guidelines for the management of arterial hypertension.1 The discrepancy in the text mirrors the debate whether a daily intake of 5 g salt or 5 g sodium (12.5 g salt) is the better recommendation. In our opinion, 2 g sodium (5 g salt) as suggested by the authors for the correction of the guideline is too low. Our thoughts favouring a sodium intake between 3 and 5 g/day are summarized below. (1) Sodium is an essential mineral with important homeostatic functions. Not surprisingly, alike other essential nutrients, the intake of sodium may be too high, too low, or optimal for meeting physiological demands.3 (2) High sodium intake is often co-linear with low-quality dietary patterns (Figure 1). Vice versa, a high intake of unprocessed, ‘healthy’ food usually goes along with low sodium but high potassium intake. This might speak to food-based instead of salt-based dietary recommendations.4 Schematic representation of relative proportions of ‘healthy’ food (green bars) as compared to processed food (red bars), which is usually rich in salt and calories. The relative amounts of such high- and low-quality diets largely determine dietary sodium intake (black line) and other food constituents, which ultimately affect the risk of hypertension. At the lower end of food intake, malnutrition may likewise translate to unfavourable adaptations like the activation of the renin–angiotensin–aldosterone system (RAAS). (3) The physiological response to dietary sodium intake is complex and may depend on underlying medical conditions. Sodium handling in the kidney underlies and feeds back to a co-ordinated balance of hormones (i.e. angiotensin II, aldosterone, vasopressin, natriuretic peptides). Hyperinsulinaemia and increased fat mass alter this balance and increase salt sensitivity. Adipose tissue, in particular ectopic adipose tissue, drives an excess in aldosterone via its endocrine, secretory function. This promotes retention of sodium and loss of potassium. Furthermore, hyperinsulinaemia affects kidney function in a way that promotes uric acid and sodium retention and hypertension. Based on these considerations, it might be prudent to primarily address adiposity and hyperinsulinaemia in the subgroup at the highest risk for salt-sensitive hypertension and cardiovascular complications by advice for an appropriate diet.5 Overall, we believe that there is too much uncertainty to justify a sodium restriction to ≤2 g/day.1 The benefit from driving sodium intake way below the global average (the mean sodium intake worldwide is 4.77 g/day)2 is questionable and potential harm cannot be excluded. We interpret the data speaking to a moderate (3–5 g/day) dietary sodium intake and suggest a critical reappraisal of the markedly lower recommendation of ≤2 g/day. A more pragmatic approach—also in the interest of global cardiovascular health and feasibility—would be the implementation of food-based rather than salt-based dietary recommendations. Protective dietary patterns are characterized by an abundance of vegetables and legumes high in potassium, moderate consumption of high-quality animal source foods, and absence of processed foods high in sodium, sugar/refined starches, and trans-fats.4 Conflict of interest: K.L. and H.S. have no competing financial interests with respect to this manuscript.