Evidence

There are a multitude of different types of studies that have examined the effects of salt on health. They range from small laboratory-based projects to large population-based investigations. While the results of individual pieces of work have varied, the totality of the evidence is incontrovertible – most of the world’s population eats far more salt than it needs and the adverse effects on global health are enormous.

Salt Intake and Blood Pressure

The clearest adverse effect of salt is on blood pressure. Observational studies comparing individuals and populations that eat different amounts of salt show a striking association of salt consumption with blood pressure. The more salt eaten, the higher is the blood pressure and the greater is the increase in blood pressure with age. And this is true not just for people with hypertension, but for the majority of the world’s population. Salt consumption is above that required for good health in most of the world’s population. Salt consumption above this level will cause some rise in the blood pressure of billions of people worldwide every year with consequent effects on the risk of stroke, heart attack, heart failure and kidney disease.

Salt Reduction and High Blood Pressure

Experimental studies confirm the observational studies. Overviews of more than thirty randomised trials in which people were assigned to eat different amounts of salt showed clear benefits of reducing salt consumption on blood pressure. And the greater the salt reduction, the greater was the blood pressure reduction. Once again, the effect was observed not just in people with hypertension but also in people with normal blood pressure levels.

Salt Reduction and Health Outcomes

There are strong data linking salt consumption to major adverse health outcomes. First, salt has clear effects on blood pressure, and high blood pressure is the biggest single cause of death in the world. Blood pressure lowering with drug therapies bring about substantially reduced risks of heart attack, stroke and heart failure and there is every expectation that the same effects would be achieved by blood pressure reduction through reduced salt consumption.

While studies of the direct effects of salt on mortality have shown varied results, the majority show adverse effects and those that do not have significant limitations in their design. Most recently, long-term follow-up of the participants of two large-scale randomised trials have shown that people assigned to reduced salt 10-15 years earlier had a 25-30% lower risk of cardiovascular events than those who continued with their usual salty diets. This evidence has greatly strengthened the argument for salt reduction.

Further Information

Summaries and Reports

Reducing Salt Intake in Populations
WHO Forum and Technical Meeting on Reducing Salt Intake in Populations.

Reviews and Meta-Analysis

He FJ, MacGregor GA. Effect of longer-term modest salt reduction on blood pressureCochrane Database Syst Rev. 2004;3:CD004937.

Gelenijnse JM, Kok FJ, Grobbee DE. Blood pressure response to changes in sodium and potassium intake: a metaregression analysis of randomised trialsJ Human Hypertens. 2003; 17:471-80.

He FJ, MacGregor GA. Effect of modest salt reduction on blood pressure: a meta-analysis of randomized trials. Implications for public healthJ Human Hypertens. 2002;16:761-70.

Key Papers

Alderman M H, Madhavan S, Cohen H, Sealey J E, Laragh J H. Low urinary sodium is associated with greater risk of myocardial infarction among treated hypertensive menHypertension. 1995;25:1144-52.

Alderman M H, Cohen H, Madhavan S. Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I)Lancet. 1998;351:781-5.

de Wardener H E. Salt reduction and cardiovascular risk: the anatomy of a mythJ Human Hypertens. 1999;13:1-4.

Denton D, Weisinger R, Mundy NI, et al. The effect of increased salt intake on blood pressure of chimpanzeesNat Med. 1995;1:1009-16.

Geleijnse JM, Hofman A, Witteman JC, et al. Long-term effects of neonatal sodium restriction on blood pressureHypertension. 1997;29:913-7.

Hofman A, Hazebroek A, Valkenburg HA. A randomized trial of sodium intake and blood pressure in newborn infantsJAMA. 1983;250:370-3.

INTERSALT. Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Intersalt Cooperative Research Group. BMJ. 1988;297:319-28.

MacGregor G A, Markandu N D, Sagnella G A, et al. Double-blind study of three sodium intakes and long-term effects of sodium restriction in essential hypertensionLancet. 1989;2:1244-7.

Nagata C, Takatsuka N, Shimizu N, Shimizu H. Sodium intake and risk of death from stroke in Japanese men and womenStroke. 2004;35:1543-7.

Page L B, Vandevert DE, Nader K, Lubin NK, Page JR. Blood pressure of Qash’qai pastoral nomads in Iran in relation to culture, diet, and body formAm J Clin Nutr. 1981;34:527-38.

Poulter NR, Khaw KT, Hopwood BE, et al. The Kenyan Luo migration study: observations on the initiation of a rise in blood pressureBMJ. 1990;300:967-72.

Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA, Harsha D, et al. Effects on blood pressure of reduced dietary sodium and the dietary approaches to stop hypertension (DASH) dietN Engl J Med. 2001;344:3-10.

Tuomilehto J, Jousilahti P, Rastenyte D, Moltchanov V, Tanskanen A, Pietinen P, Nissinen A. Urinary sodium excretion and cardiovascular mortality in Finland: a prospective studyLancet. 2001;357:848-51.