Reducing sodium and increasing potassium intakeBMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f2195 (Published 09 April 2013) Cite this as: BMJ 2013;346:f2195
- Pasquale Strazzullo, professor of medicine
- 1Department of Clinical Medicine and Surgery, Federico II University of Naples Medical School, 80131 Naples, Italy
Hypertension and its associated cardiovascular and renal complications is a global health problem that imposes a heavy burden in terms of individual disability and financial costs to individuals and communities. Prevention and treatment of hypertension therefore is a major challenge to health institutions. The recommendation to reduce dietary sodium intake has been incorporated into guidelines for preventing and treating hypertension for decades, yet it is widely ignored even by patients with hypertension. In addition, despite the robust evidence that underlies a reduction in sodium intake, its implementation at the population level remains the object of recurrent criticism, with counterarguments often based on confounded study results or analyses that lack statistical power.1
Two linked research papers that focus on the effects of reduced sodium intake on blood pressure and related health problems are timely and may help dissipate the public’s doubts about the value of reducing sodium intake.2 3 Another linked paper examines the health effects of higher potassium intake in adults and children and adds to earlier findings of an inverse association between potassium intake, as well as fruit and vegetable consumption, and blood pressure.4 5 Of note, the Department of Nutrition for Health and Development of the World Health Organization was directly involved in two of the three articles, and the results were used in the compilation of the recently updated WHO guidelines on sodium and potassium intake at population level.6 7
All three linked papers are systematic reviews and were conducted according to Cochrane Collaboration recommended methods. All report the results of updated meta-analyses of the findings of relevant studies conducted in healthy people (studies that recruited patients with major illnesses or diabetes were excluded). The authors mainly considered the results of randomised controlled trials of dietary interventions, but cohort studies were also included when information from such trials was unavailable or inconclusive.
The analysis by Aburto and colleagues and that by He and colleagues provide high quality evidence that moderately reduced sodium intake significantly reduces blood pressure in both hypertensive and normotensive adults, independent of sex. Meta-regression and subgroup analyses in both studies suggest a dose-effect relation between reduced sodium intake and blood pressure—the larger the reduction in salt intake the greater the effect on blood pressure down to salt intake of less than 3 g per day. The estimated falls of 10.8 mm Hg and 4.3 mm Hg in systolic blood pressure associated with a 6 g per day reduction in salt intake in hypertensive and normotensive adults, respectively, are impressive. Accordingly, such a dietary modification would be expected to greatly reduce the incidence of stroke and other cardiovascular events if extended to the whole population. A significant, albeit small, decrease in systolic blood pressure was also seen in an analysis of the findings of trials of reduced salt intake in children.
Reductions in salt intake of the size reported in the current studies were not associated with clinically important changes in blood lipids or a decline in renal function or sympathetic activation, and they led to only minor stimulation of the renin-angiotensin-aldosterone system. These results highlight that the significant changes in neuroendocrine and metabolic factors reported in previous studies occur only with brisk, short term, and extreme reductions in salt intake that are well beyond the range of guideline recommendations.8
Aburto and colleagues’ analysis of the relation between sodium intake and major cardiovascular outcomes confirms the strong direct association between habitual sodium intake and the incidence of stroke reported by a previous meta-analysis,9 after incorporating a few recently published studies. Moreover, it provides new evidence of a significant direct association between higher sodium intake and the incidence of fatal stroke and fatal coronary events. This evidence comes from cohort studies because of the lack of trials. Nevertheless, it is strongly supported by the robust evidence of the effect of reducing sodium intake on blood pressure—in almost all trials conducted so far, even modest differences in blood pressure were associated with substantial differences in the rate of stroke.
Aburto and colleagues’ second study provides high quality evidence of the beneficial effect of increasing potassium intake on blood pressure in people with hypertension, again with no evidence of untoward metabolic, neuroendocrine, or renal effects in adults free of major illnesses. It also confirms the recently reported inverse association of potassium intake with the risk of stroke,10 a conclusion based on cohort studies.
In most countries, most people—even those with hypertension—consume much more sodium and less potassium than is recommended. The current results should prompt doctors and public health professionals to maximise efforts to increase patients’ awareness and motivation regarding the benefits of reducing salt intake (ideally to less than 3 g per day) and of increasing the consumption of potassium-rich foods. To increase the chances that these efforts are successful, national strategies to support reduced salt intake at the population level are crucial and negotiations with food industry for the reformulation of most processed foods should be undertaken as a matter of urgency.11
In addition, the well known excess salt intake in children deserves greater attention and more intensive intervention.12 Because the effects of reduced sodium intake on blood pressure become progressively greater with advancing age, as shown in Aburto and colleagues’ and He and colleagues’ meta-analyses, policy makers may overlook the progressive, yet difficult to detect, vascular damage prematurely caused by excess salt intake in young people. Thus, research should be aimed at identifying more sensitive indicators of the harmful effects of high sodium intake in children and adolescents.
Cite this as: BMJ 2013;346:f2195
Competing interests: I/we have read and understood the BMJ Group policy on declaration of interests and declare the following interests: PS is an unpaid member of World Action on Salt and Health (WASH), coordinator of the Interdisciplinary Working Group for Reduction of Salt Intake in Italy (GIRCSI), a member of the SINU/INRAN committee for the preparation of the Italian dietary reference intakes, and a former member and treasurer of the executive committee of the Italian Society of Hypertension.
Provenance and peer review: Commissioned; not externally peer reviewed.