Reducing Population Salt Intake Worldwide: From Evidence to Implementation

https://doi.org/10.1016/j.pcad.2009.12.006Get rights and content

Abstract

Raised blood pressure is a major cause of cardiovascular disease, responsible for 62% of stroke and 49% of coronary heart disease. There is overwhelming evidence that dietary salt is the major cause of raised blood pressure and that a reduction in salt intake lowers blood pressure, thereby, reducing blood pressure-related diseases. Several lines of evidence including ecological, population, and prospective cohort studies, as well as outcome trials, demonstrate that a reduction in salt intake is related to a lower risk of cardiovascular disease. Increasing evidence also suggests that a high salt intake may directly increase the risk of stroke, left ventricular hypertrophy, and renal disease; is associated with obesity through soft drink consumption; is related to renal stones and osteoporosis; is linked to the severity of asthma; and is probably a major cause of stomach cancer. In most developed countries, a reduction in salt intake can be achieved by a gradual and sustained reduction in the amount of salt added to foods by the food industry. In other countries where most of the salt consumed comes from salt added during cooking or from sauces, a public health campaign is needed to encourage consumers to use less salt. Several countries have already reduced salt intake. The challenge now is to spread this out to all other countries. A modest reduction in population salt intake worldwide will result in a major improvement in public health.

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)

  • St-OngeM.P. et al.

    Changes in childhood food consumption patterns: a cause for concern in light of increasing body weights

    Am J Clin Nutr

    (2003)
  • CappuccioF.P. et al.

    Double-blind randomised trial of modest salt restriction in older people

    Lancet

    (1997)
  • LiJ. et al.

    Salt inactivates endothelial nitric oxide synthase in endothelial cells

    J Nutr

    (2009)
  • DickinsonK.M. et al.

    Effects of a low-salt diet on flow-mediated dilatation in humans

    Am J Clin Nutr

    (2009)
  • AntoniosT.F. et al.

    Salt-more adverse effects

    Lancet

    (1996)
  • KarppanenH. et al.

    Sodium intake and hypertension

    Prog Cardiovasc Dis

    (2006)
  • AldermanM.H. et al.

    Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I)

    Lancet

    (1998)
  • KarppanenH. et al.

    Sodium intake and mortality

    Lancet

    (1998)
  • BrownI.J. et al.

    Salt intakes around the world: implications for public health

    Int J Epidemiol

    (2009)
  • Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion

    BMJ

    (1988)
  • HeF.J. et al.

    A comprehensive review on salt and health and current experience of worldwide salt reduction programmes

    J Hum Hypertens

    (2009)
  • CookN.R. et al.

    Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP)

    BMJ

    (2007)
  • CianciarusoB. et al.

    Salt intake and renal outcome in patients with progressive renal disease

    Miner Electrolyte Metab

    (1998)
  • SwiftP.A. et al.

    Modest salt reduction reduces blood pressure and urine protein excretion in black hypertensives: a randomized control trial

    Hypertension

    (2005)
  • PerryI.J. et al.

    Salt intake and stroke: a possible direct effect

    J Hum Hypertens

    (1992)
  • NagataC. et al.

    Sodium intake and risk of death from stroke in Japanese men and women

    Stroke

    (2004)
  • KupariM. et al.

    Correlates of left ventricular mass in a population sample aged 36 to 37 years. Focus on lifestyle and salt intake

    Circulation

    (1994)
  • HeF.J. et al.

    Effect of salt intake on renal excretion of water in humans

    Hypertension

    (2001)
  • HeF.J. et al.

    Salt intake is related to soft drink consumption in children and adolescents: a link to obesity?

    Hypertension

    (2008)
  • CappuccioF.P. et al.

    Unravelling the links between calcium excretion, salt intake, hypertension, kidney stones and bone metabolism

    J Nephrol

    (2000)
  • TsuganeS. et al.

    Salt and salted food intake and subsequent risk of gastric cancer among middle-aged Japanese men and women

    Br J Cancer

    (2004)
  • LewingtonS. et al.

    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

    (2002)
  • DentonD. et al.

    The effect of increased salt intake on blood pressure of chimpanzees

    Nat Med

    (1995)
  • ElliottP. et al.

    Change in salt intake affects blood pressure of chimpanzees: implications for human populations

    Circulation

    (2007)
  • PageL.B. et al.

    Antecedents of cardiovascular disease in six Solomon Islands societies

    Circulation

    (1974)
  • Uzodike VO: Epidemiological studies of arterial blood pressure and hypertension in relation to electrolyte excretion in...
  • ElliottP. et al.

    Evidence on salt and blood pressure is consistent and persuasive

    Int J Epidemiol

    (2002)
  • ElliottP. et al.

    Intersalt revisited: further analyses of 24 hour sodium excretion and blood pressure within and across populations

    BMJ

    (1996)
  • ZhouB.F. et al.

    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

    (2003)
  • HeJ. et al.

    Migration, blood pressure pattern, and hypertension: the Yi Migrant Study

    Am J Epidemiol

    (1991)
  • PoulterN.R. et al.

    The Kenyan Luo migration study: observations on the initiation of a rise in blood pressure

    BMJ

    (1990)
  • ForteJ.G. et al.

    Salt and blood pressure: a community trial

    J Hum Hypertens

    (1989)
  • TianH.G. et al.

    Changes in sodium intake and blood pressure in a community-based intervention project in China

    J Hum Hypertens

    (1995)
  • StaessenJ. et al.

    Salt intake and blood pressure in the general population: a controlled intervention trial in two towns

    J Hypertens

    (1988)
  • TuomilehtoJ. et al.

    Community-based prevention of hypertension in North Karelia, Finland

    Ann Clin Res

    (1984)
  • TakahashiY. et al.

    Blood pressure change in a free-living population-based dietary modification study in Japan

    J Hypertens

    (2006)
  • LawM.R. et al.

    By how much does dietary salt reduction lower blood pressure? III-Analysis of data from trials of salt reduction

    BMJ

    (1991)
  • MidgleyJ.P. et al.

    Effect of reduced dietary sodium on blood pressure: a meta-analysis of randomized controlled trials

    JAMA

    (1996)
  • GraudalN.A. et al.

    Effects of sodium restriction on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride: a meta-analysis

    JAMA

    (1998)
  • HooperL. et al.

    Systematic review of long term effects of advice to reduce dietary salt in adults

    BMJ

    (2002)
  • Cited by (449)

    View all citing articles on Scopus

    Statement of Conflict of Interest: see page 378.

    View full text