Salt- Heart Disease and Industry

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There is of course a well-known relationship between sodium chloride and hypertension[1] and we all make comments when we see the enthusiastic application of table salt onto food or add in the making of food. These are the visible uses of this flavour enhancer, but it is the salt used in food manufacturing that represents the largest exposure for most people.

A recent paper out in Nov 2010 in the BMJ Heart & Education explores the painfully slow progress towards suitable reductions.[2] Many countries do recommend restricting daily sodium intake to 100 mmol (approximately 6 g of table salt) or less, but in a recent review of world salt levels, only seven out of the 25 countries reviewed met this goal suggesting a lack of legislative pressure and social interest.[3]

In countries in which a western style diet is consumed some 75% of all ingested salt comes from food processing techniques.[4] We all recognise that our initial enthusiasm with clients and patients for total salt reduction can reduce consumption through immediate changes in behaviour, but this is attenuated over time making what little gains in BP that were initially achieved too small to impact on significant numbers of the population.

Many countries, including Finland, the USA, the UK, Canada, France, Australia and New Zealand, have implemented salt reduction programmes based on product reformulation, labelling and/or public education to inform and encourage change in individual dietary choices and food industry practices.[5] The population health benefits, however, are largely unknown except in Finland where the use of a replacement salt was made part of public health policy and included; Potassium, half the sodium of normal table salt and, more importantly, adds magnesium, potassium, lysine and iodine.[6]

Adherence to antihypertensive drug therapy has been quite good. However, the drug treatment does not seem to account for more than 5-6 % of the observed fall of blood pressure, and 10-15 % of the decrease in deaths from strokes and ischaemic heart disease. The report went on to note that during the same time period …marked increases in the intake of alcohol, obesity among men, and smoking among women have been observed.

A follow up review noted that during the past 30 years, the one-third decrease in the average salt intake has been accompanied by a more than 10-mm Hg fall in the population average of both systolic and diastolic blood pressure, and a 75% to 80% decrease in both stroke and coronary heart disease mortality in Finland.[7]

These are impressive improvements in mortality for a single intervention – if this was been achieved by medication the results would be lauded from all points of the media. Salt replacement may not be sexy but reducing sodium and increasing potassium in the diet has a dramatic impact on cardiovascular outcomes and represents the single most effective public health policy anywhere.

Overall, Cobiac and her colleagues calculated, 610,000 disability-adjusted life years could be avoided over the course of the lifetime of the population if everyone reduced their salt intake to recommended limits.

Salt Reduction is better than Cholesterol, Smoking and Weight Loss

Simulations in the USA even suggest that achieving a salt reduction of 3 g/day in the American diet (approximately 29% of daily intake for men and 41% for women) could benefit public health more than targeting tobacco, weight loss or cholesterol levels, and prevent as many deaths as antihypertensive drugs would prevent if given to everyone with hypertension.[8]

It is not clear, however, if salt reductions of this magnitude are achievable with current measures that rely on voluntary changes by food manufacturers and informed choice by consumers.

Comment

Salt is added to processed foods for many reasons; to entice further consumption, to bulk a product up cheaply by increasing water-holding capacity, or to promote drink sales by increasing thirst. The idea that an alternative to salt may prevent CV disease by an amazing 75-80% suggests that the food industry looking to add value to their products would do well to exchange this ingredient quickly and the national government may be persuaded to seek legislation not to add or fortify as with folic acid, but to remove an ingredient closely linked to poor health and reduce the enormous economic burden related to CV disease.

References


[1] Law MR, Frost CD, Wald NJ. By how much does dietary salt reduction lower blood-pressure? 1. Analysis of observational data among populations. BMJ 1991;302:811–15. View Abstract

[2] Cobiac LJ, Vos T, Veerman JL. Cost-effectiveness of interventions to reduce dietary salt intake.Heart. 2010 Nov 1 View Abstract

[3] Brown I,Tzoulaki I, Candeias V, et al. Salt intakes around the world: implications for public health. Int J Epidemiol 2009;38:791–813. View Full Paper

[4] Mattes RD, Donnelly D. Relative contributions of dietary sodium sources. J Am Coll Nutr 1991;10:383–93 View Abstract

[5] Mohan S, Campbell NRC, Willis K. Effective population-wide public health interventions to promote sodium reduction. Can Med Assoc J 2009;181:605–9 View Abstract

[6] Karppanen H, Mervaala E. Adherence to and population impact of non-pharmacological and pharmacological antihypertensive therapy. J Hum Hypertens. 1996 Feb;10 Suppl 1:S57-61. View Abstract

[7] Karppanen H, Mervaala E. Sodium intake and hypertension. Prog Cardiovasc Dis. 2006 Sep-Oct;49(2):59-75. Review. View Abstract

[8] Bibbins-Domingo K, Chertow GM, Coxson PG, et al. Projected effect of dietary salt reductions on future cardiovascular disease. N Engl J Med 2010;362:590–9. View Abstract

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2 Comments. Leave new

  • I was under the impression that salt was no longer the monster it has always been held to be with relation to high blood pressure and that genetics plays a much stronger role in whether salt is a problem for an individual.

    The idea being that there is an association between salt intake and HBP, but that this is due to a poor diet low in other minerals such as magnesium, and the connection is not a causal one.
    http://www.ukprwire.com/Detailed/Health_Wellbeing/SALT_POLICY_COULD_BE_A_DISASTER_WAITING_TO_HAPPEN__8552.shtml

    Reply
    • Hi Roger
      The relationship between salt (sodium chloride) and hypertension – in relation to increased intake of sodium is understood and generally accepted to be causal, albeit that it is competetively inhibited in its effects by the inclusion of amongst other minerals – potassium.

      It is not true to say as the nutritionist quoted in the linked article says that there has been no long term population based studies, the Finnish experiment described in my article was repeated in Australia and Thailand, albeit in smaller numbers.

      In the Taiwanese study, the researchers examined the effects of a potassium-enriched salt on cardiovascular disease mortality and medical expenditures in elderly veterans. Five kitchens of a retirement home serving 1,981 veterans were randomised into two groups, “experimental” using potassium-enriched salt or “control” using regular (sodium-chloride) salt.
      After 31 months, researchers observed a significant reduction in cardiovascular disease mortality in the “experimental” salt group. The people in the potassium-enriched salt group also spent significantly less for in-patient care for cardiovascular disease than people in the control group. The researchers concluded: “The effect was likely due to a major increase in potassium and a moderate reduction in sodium intakes.” http://www.ncbi.nlm.nih.gov/pubmed/10578223

      And earlier last year (2009), researchers from Harvard Medical School reported that urinary sodium/potassium ratios have predictive value, too. They concluded: “A higher sodium to potassium excretion ratio is associated with increased risk of subsequent cardiovascular disease.” They also noted that the actual ratio of the nutrients is a stronger predictor than either one on its own. http://www.ncbi.nlm.nih.gov/pubmed/19139321

      I would suggest that he has some evidential base for his comments, and certainly seeing a greater consumption of vegetables overall is to be recommended, but public health policies are broad brushes and the remarkable benefits seen by Finland in the salt replacement strategy deserves a serious review by the UK and other governments.

      Reply

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