Reducing Population Salt Intake Worldwide: From Evidence to Implementation
Section snippets
Salt and sodium
The terms salt and sodium are often used synonymously. However, on a weight basis, salt comprises 40% sodium and 60% chloride. The conversion of different units for sodium and salt is as follows: 1 g sodium = 2.5 g salt; 1 mmol sodium = 23 mg sodium; 1 g salt = 0.4 g sodium; and 1 g salt = 17 mmol sodium. Salt is the major source of sodium in the diet (approximately 90%). Throughout this review, we use the term salt for simplicity.
Salt and BP
Raised BP is a major cause of CVD, responsible for 62% of stroke and 49% of coronary heart disease. Importantly, the risk of CVD increases throughout the range of BP, starting at 115/75 mm Hg.17 It has been shown that a high salt intake, a low consumption of fruit and vegetables (ie, low potassium intake), obesity, excess alcohol intake, and lack of physical exercise all contribute to the development of high BP. However, the diversity and strength of the evidence is much greater for salt than
Infants
A meta-analysis of 3 controlled trials with 551 infants showed that a 54% reduction in salt intake for an average duration of 20 weeks reduced systolic BP by 2 mm Hg (P < .01). Among the 3 trials included in the meta-analysis, 2 were carried out in the early 1970s and 1980s, and at that time, salt concentrations in formula milk were approximately 3 times higher than in human milk.46 Currently, in most developed countries, salt is no longer added to formula milk or baby foods, and salt
Variations in BP response to salt reduction
Randomized trials have shown that, for a given reduction in salt intake, the falls in BP were larger in individuals of African origin, in older people, and in those with raised BP compared to whites, young people, and those with normal BP, respectively.59 The greater decreases in BP in these individuals were, at least in part, due to the diminished responsiveness of their renin-angiotensin system.56, 60
The term “salt sensitivity” has been commonly used to describe the variations of BP response
Salt and other dietary and lifestyle changes for lowering BP
There is evidence that a reduction in salt intake is additive to other dietary and lifestyle changes for lowering BP.45, 62 The DASH (Dietary Approaches to Stop Hypertension)-Sodium trial,45 a well-controlled feeding trial, studied 3 levels of salt intake (8, 6, and 4 g/d) on 2 different diets, that is, the normal American diet and the DASH diet, which is rich in fruits, vegetables, and low-fat dairy products. The study demonstrated that a reduction in salt intake lowered BP both on the normal
Salt and antihypertensive treatments
Randomized trials have demonstrated that a reduction in salt intake causes further decreases in BP in individuals who are already on antihypertensive drug treatments. It also enhances BP control and reduces the need for antihypertensive drug therapy.62, 64 Salt restriction is particularly effective in lowering BP when the renin-angiotensin system is blocked by an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker because the reactive increase in plasma renin activity and
Role of the kidneys
The mechanisms whereby salt raises BP are not fully understood. However, there is much evidence that individuals who develop high BP have an underlying defect in the kidneys' ability to excrete sodium. The kidney cross-transplantation experiments clearly demonstrated the important role of the kidneys in BP regulation.67, 68 When a kidney from a normotensive rat was inserted into a young bilaterally nephrectomized spontaneously hypertensive rat, the BP of the hypertensive rat did not rise, and
Salt and CVD
A reduction in salt intake lowers BP, and as raised BP throughout its range is a major risk factor for CVD, this would be predicted to reduce CVD. Based on the falls in BP from a meta-analysis of randomized salt reduction trials,43 it was estimated that a reduction of 6 g/d in salt intake would reduce stroke by 24% and coronary heart disease (CHD) by 18%. This would prevent approximately 35,000 stroke and CHD deaths a year in the United Kingdom84 and approximately 2.5 million deaths worldwide.
Other harmful effects of salt
There is increasing evidence that salt has other deleterious effects on health, independent of and sometimes additive to its effect on BP.
Salt and the renin-angiotensin system, the sympathetic nervous system, lipids, and insulin sensitivity
When salt intake is reduced, there is a physiologic stimulation of the renin-angiotensin system and the sympathetic nervous system. These compensatory responses are bigger with sudden and large decreases in salt intake and much smaller or minimal with a modest reduction in salt intake for a more prolonged period, which is the current public health recommendation on population salt intake. Randomized trials have demonstrated that, with a longer term modest reduction in salt intake, there was
Cost-effectiveness of reducing population salt intake
Several studies have demonstrated that a reduction in population salt intake is very cost-effective.142, 143, 144, 145 For example, Murray et al145 showed that nonpersonal health interventions, including government action to stimulate a reduction in the salt content of processed foods, were cost-effective ways to limit CVD and could avert more than 21 million disability-adjusted life years per year worldwide. A study in Norwegian population documented that a 6 g/d reduction in salt intake with
Worldwide salt reduction programs
Many countries have developed their own guidelines on dietary salt intake. The United Kingdom and US guidelines recommend salt intake of less than 6 g/d for adults.146, 147 The WHO set a worldwide target of a maximum intake of 5 g/d.148 Through its regional directorates, the WHO is starting salt reduction strategies.149 Eleven countries in the European Union have signed up to make a 16% reduction in salt intake over the next 4 years.150 Several countries, for example, Finland, the United
The role of the food industry in salt reduction
In most developed countries, approximately 80% of salt we eat is added to foods at the stage of manufacturing,164 and the consumers have no say over how much salt is added. Therefore, to achieve a reduction in population salt intake, it is imperative that the food industry reduces the amount of salt they add to all foods. In view of the compelling evidence on the benefits of salt reduction, most food companies recognize that it is time to initiate salt reduction programs and start the process
Conclusions
There is now overwhelming evidence for a reduction in salt intake in populations worldwide. Reducing salt from the current intake of 9 to 12 g/d to the recommended level of 5 to 6 g/d will have a major effect on BP and thereby CVD and may have other beneficial effects on health as outlined in this article.
All countries should adopt a coherent and workable strategy to reduce salt intake in the whole population. In most developed countries, approximately 80% of salt is hidden in foods, that is,
Statement of Conflict of Interest
All authors declare that there are no conflicts of interest.
References (164)
- et al.
Urinary sodium excretion and cardiovascular mortality in Finland: a prospective study
Lancet
(2001) - et al.
Efficacy and variability of the antiproteinuric effect of ACE inhibition by lisinopril
Kidney Int
(1989) A diet rich in sodium may potentiate asthma. Epidemiologic evidence for a new hypothesis
Chest
(1987)- et al.
Molecular mechanisms of human hypertension
Cell
(2001) - et al.
Blood pressure of Qash'qai pastoral nomads in Iran in relation to culture, diet, and body form
Am J Clin Nutr
(1981) - et al.
Blood pressure and urinary sodium in men and women: the Norfolk Cohort of the European Prospective Investigation into Cancer (EPIC-Norfolk)
Am J Clin Nutr
(2004) Treatment of hypertensive vascular disease with rice diet
Am J Med
(1948)- et al.
Double-blind randomised crossover trial of moderate sodium restriction in essential hypertension
Lancet
(1982) - et al.
Randomized trials of sodium reduction: an overview
Am J Clin Nutr
(1997) - et al.
Double-blind study of three sodium intakes and long-term effects of sodium restriction in essential hypertension
Lancet
(1989)
Changes in childhood food consumption patterns: a cause for concern in light of increasing body weights
Am J Clin Nutr
Double-blind randomised trial of modest salt restriction in older people
Lancet
Salt inactivates endothelial nitric oxide synthase in endothelial cells
J Nutr
Effects of a low-salt diet on flow-mediated dilatation in humans
Am J Clin Nutr
Salt-more adverse effects
Lancet
Sodium intake and hypertension
Prog Cardiovasc Dis
Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I)
Lancet
Sodium intake and mortality
Lancet
Salt intakes around the world: implications for public health
Int J Epidemiol
Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion
BMJ
A comprehensive review on salt and health and current experience of worldwide salt reduction programmes
J Hum Hypertens
Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP)
BMJ
Salt intake and renal outcome in patients with progressive renal disease
Miner Electrolyte Metab
Modest salt reduction reduces blood pressure and urine protein excretion in black hypertensives: a randomized control trial
Hypertension
Salt intake and stroke: a possible direct effect
J Hum Hypertens
Sodium intake and risk of death from stroke in Japanese men and women
Stroke
Correlates of left ventricular mass in a population sample aged 36 to 37 years. Focus on lifestyle and salt intake
Circulation
Effect of salt intake on renal excretion of water in humans
Hypertension
Salt intake is related to soft drink consumption in children and adolescents: a link to obesity?
Hypertension
Unravelling the links between calcium excretion, salt intake, hypertension, kidney stones and bone metabolism
J Nephrol
Salt and salted food intake and subsequent risk of gastric cancer among middle-aged Japanese men and women
Br J Cancer
Age-specific relevance of usual blood pressure to vascular mortality: a meta-analysis of individual data for one million adults in 61 prospective studies
Lancet
The effect of increased salt intake on blood pressure of chimpanzees
Nat Med
Change in salt intake affects blood pressure of chimpanzees: implications for human populations
Circulation
Antecedents of cardiovascular disease in six Solomon Islands societies
Circulation
Evidence on salt and blood pressure is consistent and persuasive
Int J Epidemiol
Intersalt revisited: further analyses of 24 hour sodium excretion and blood pressure within and across populations
BMJ
Nutrient intakes of middle-aged men and women in China, Japan, United Kingdom, and United States in the late 1990s: the INTERMAP study
J Hum Hypertens
Migration, blood pressure pattern, and hypertension: the Yi Migrant Study
Am J Epidemiol
The Kenyan Luo migration study: observations on the initiation of a rise in blood pressure
BMJ
Salt and blood pressure: a community trial
J Hum Hypertens
Changes in sodium intake and blood pressure in a community-based intervention project in China
J Hum Hypertens
Salt intake and blood pressure in the general population: a controlled intervention trial in two towns
J Hypertens
Community-based prevention of hypertension in North Karelia, Finland
Ann Clin Res
Blood pressure change in a free-living population-based dietary modification study in Japan
J Hypertens
By how much does dietary salt reduction lower blood pressure? III-Analysis of data from trials of salt reduction
BMJ
Effect of reduced dietary sodium on blood pressure: a meta-analysis of randomized controlled trials
JAMA
Effects of sodium restriction on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride: a meta-analysis
JAMA
Systematic review of long term effects of advice to reduce dietary salt in adults
BMJ
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Statement of Conflict of Interest: see page 378.