Policy options to reduce population salt intakeBMJ 2011; 343 doi: http://dx.doi.org/10.1136/bmj.d4995 (Published 11 August 2011) Cite this as: BMJ 2011;343:d4995
- Francesco P Cappuccio, Cephalon professor of cardiovascular medicine and epidemiology, head of WHO collaborating centre1,
- Simon Capewell, chair of clinical epidemiology2,
- Paul Lincoln, chief executive 3,
- Klim McPherson, visiting professor of public health epidemiology4
- 1University of Warwick, Warwick Medical School, WHO Collaborating Centre for Nutrition, Coventry CV2 2DX, UK
- 2University of Liverpool, Liverpool, UK
- 3National Heart Forum, London, UK
- 4University of Oxford, Oxford, UK
- Correspondence to: F P Cappuccio
- Accepted 31 July 2011
Blood pressure and cardiovascular disease
Raised blood pressure is the dominant cause of death and disability in adults worldwide,1 responsible for approximately 50% of deaths from coronary heart disease and over 60% of those from stroke. The risk of cardiovascular disease increases with increasing blood pressure,2 and causality is supported by randomised controlled clinical trials, in which lowering blood pressure over five years reduces cardiovascular disease by approximately the amount predicted from larger observational studies.3 But the majority of cardiovascular disease events attributable to blood pressure occur in people with untreated “normal” pressure (about 130/80 mm Hg), with additional events occurring even with blood pressure levels down to 115/75 mm Hg. 2 Even a small downward shift in the distribution of blood pressure in the whole population would achieve a large drop in cardiovascular disease.2
Evidence relating salt to blood pressure
Evidence from a very wide variety of studies shows a consistent direct relation between salt intake and blood pressure. A 4.6 g reduction in daily dietary intake of salt (equivalent to a 1840 mg reduction in daily sodium) decreases blood pressure by about 5.0/2.7 mm Hg in individuals with hypertension and by 2.0/1.0 mm Hg in normotensive people.4 Randomised controlled trials have consistently shown dose-response effects.5 The blood pressure lowering effect of reducing salt intake is effective in men and women, in all ethnic groups, in all age groups, and all starting blood pressures.
Population based interventions indicate that when salt intake is reduced, blood pressure in the community falls. An intervention study in two Portuguese villages over two years achieved a difference between intervention and control villages of about 50% in salt intake and a difference of 13/6 mm Hg in blood pressure.6 A randomised community based intervention trial in villages in northeastern Japan, which tested the effects of dietary counselling for one year, reduced mean salt intake by 2.3 g/day (920 mg of sodium) as measured by 24 h urinary sodium, and was associated with a decrease of 3.1 mm Hg in systolic blood pressure.7 Citizens in most countries eat salt far in excess of healthy physiological requirements (about 1 g per day).
Evidence relating salt to cardiovascular disease
No randomised controlled trials have studied the effect of reducing the salt intake of populations on cardiovascular disease—the ethical and methodological problems with such trials are similar to those with trials involving tobacco and obesity8—but the link is strong and is now accepted. In cohort studies, a 5 g per day higher salt intake (2000 mg of sodium) is associated with a 17% greater risk of total cardiovascular disease, and, crucially a 23% greater risk of stroke.9
Since the 1970s, Finland has aimed to reduce the population’s salt intake10 by collaboration with the food industry to develop food products with reduced salt and by raising awareness among consumers. Over 30 years salt intake has reduced by a third (6 g per person per day). Systolic blood pressure fell by over 10 mm Hg, while mortality from stroke and coronary heart disease decreased 75-80%, with an increase of five to six years in life expectancy.10 Similarly, in Japan, a government campaign to reduce salt intake saw a fall from 13.5 g/day to 12.1 g/day (from 5400 mg to 4840 mg sodium) in a decade. This was associated with a substantial reduction in stroke mortality,11 despite increases in the population’s fat intake, cigarette smoking, alcohol consumption, and body mass index.
The economic imperative
All countries need to satisfy stringent cost effectiveness criteria within a general climate of ageing populations, escalating healthcare demands, and recently reduced financial resources. Several economic modelling studies have assessed the health effects and financial cost of reducing population salt intake. Despite methodological differences, they all have consistently shown that a reduction in salt intake is associated with substantial cost savings (see webtable and web referencesw1-w12). For example, in the United States, a mean population salt reduction of 3 g per day would result in an estimated annual gain of 194 000-392 000 quality adjusted life years (QALYs), a measure of added healthy life, and savings of $10bn to $24bn (£6-15bn, €7-17bn) in healthcare costs.w11 This represents a $6-12 return on investment for each dollar spent on the regulatory programme. Cost savings are also estimated for a reduction in salt intake of 15% in low and middle income countries, with 13.8 million deaths averted over 10 years at an initial cost of less than $0.40 per person per year.w5
The prevention imperative
Unsurprisingly, the prevention of cardiovascular disease is now agreed as a top priority for action worldwide.12 Among the five priority interventions, reduction of populations’ salt intake is listed as second after global tobacco control. It is estimated that a 15% reduction in salt intake would avert 8.5 million deaths over 10 years worldwide.
The global goal set by WHO is to reduce salt intake to less than 5 g (2000 mg of sodium) per person per day by 2025,12 with some countries aiming for even lower levels in the longer term (table 1⇓).w13-w20 Progress towards this target could begin through mass media campaigns and reformulation of existing and new food products by industry. Since in most developed economies the majority of dietary salt is added during commercial food production, government regulation will also be needed.12 13
Many countries have committed themselves to salt reduction initiatives, often led by government, sometimes led by non-governmental organisations, but rarely led by industry (table 2⇓).14 In 2004 the British government, through the Food Standards Agency, started a programme of population salt reduction through a media campaign to increase public awareness and demand for change, engagement with the food industry on a voluntary basis to set targets for sodium content in foods, and to obtain reformulation of many common food categories, and repeated national surveys using 24 h urine collections to monitor intake. Ministers also proposed legislation if the industry refused to make reductions voluntarily. As a result the mean salt intake in the UK fell from 9.5 g (3800 mg sodium) per day in 2001 to 8.6 g (3440 mg sodium) per day in 2008. In England and Wales, the government target is now 6 g (2400 mg sodium) per day by 2012, sadly remaining higher than the target of 4 g (1600 mg sodium) per day achieved in the US DASH trial and of 3 g (1200 mg sodium) recommended by NICE by 2025.15 A reduction of 3 g per day in salt intake would result in a blood pressure fall of at least 2.5/1.4 mm Hg.15 This would reduce strokes by about 12-14% and coronary heart disease by 9-10%,9 15 equivalent to approximately 6500-8000 deaths from stroke and 7500-12 000 deaths from coronary heart disease per year.15
In the United States, a reduction in salt intake of 3 g per day would reduce the annual number of new cases of cardiovascular disease by approximately 10% (around 60 000-120 000 fewer cases of coronary heart disease, 32 000-66 000 strokes, and 54 000-99 000 heart attacks) with a corresponding reduction in all cause mortality.w11 The expected reductions in vascular events would be comparable with those currently projected for interventions targeting tobacco, obesity, or primary prevention with statins and antihypertensives.w5
Changing salt policies and perceived barriers
As with tobacco, some vested interests in the salt and food industries are fighting a rearguard action. The salt industry is reluctant to facilitate a reduction in salt intake across populations, but not because their major market is in food; less than 10% of the salt sold worldwide enters the food chain. Yet the use of salt in food is indirectly a source of revenue for food and beverage manufacturers more widely. High salt intake downregulates taste buds for saltiness, and makes food more palatable, thus increasing demand. Salt in meat products, in conjunction with other water binding chemicals, increases the amount of water that can be bound into the meat, increasing weight by up to 20% at no cost. High salt intake increases thirst and demand for sugary drinks.10 These increase calorie intake, particularly in younger people who are major consumers, thus contributing to obesity.16
The UK experience indicates that in the early stages of a salt reduction programme it is possible to take 5-15% of the salt out of a product gradually without noticeable change in flavour, sales, or complaints about taste. As salt intake falls, the salt taste receptors in the mouth adapt and become more sensitive to lower concentrations of salt within months.17 Once salt intake is reduced, people prefer the taste of food with less salt.18
Reports of paradoxical increases in cardiovascular risk in those on a low sodium intake have recently sparked some debate.w21-w24 However, these studies are seriously flawed.w25-w28
The International Council for the Control of Iodine Deficiency Disorders estimates that about 1.5 billion people worldwide live in areas of iodine deficiency. In 1996, in conjunction with WHO and Unicef, they started a universal salt iodisation programme, using salt as a vehicle to deliver supplementary iodine in the diet. If salt intake is reduced, these policies will remain compatible, cost effective, and of great public health benefit, if the level of iodine fortification can be adjusted to changing sodium intake.
Various policy interventions are currently being tested or implemented worldwide through national and international initiatives (table 3⇓).14 International schemes have led to high level agreements among many governments for the implementation of national programmes to reduce population dietary salt for the prevention of cardiovascular disease. Salt substitution policies are being tested in China, where this alternative approach might be feasible. However, a regulatory approach is both necessary and acceptable,13 as demonstrated in Finland. This is more effective and cost effective than the voluntary approach alone.w12
Health policy makers and governments have to decide how best to reduce population salt intake at a population level, to save most lives and public money in shrinking economies; likewise, in low and middle income countries with very limited budgets, how best to afford cheaper and effective planning to prevent, ameliorate, and control their rapidly increasing burden of non-communicable diseases.
Changing personal behaviour and choice alone is not an effective or realistic option when the majority of salt is added to food before it is sold and food marketing relies on taste. Furthermore, the commercial addition of salt to food is becoming a global trend as the worldwide food economy changes. A four pronged approach is therefore required and should form the base for a comprehensive policy:
Communication—establishing and evaluating public awareness campaigns
Reformulation—setting progressive salt targets for reformulating existing processed food and engaging with the food industry in setting standards for new foods
Monitoring—surveying population salt intake, progress of reformulation, and effectiveness of communication
Regulation—engagement with industry, including regulation, to create a level playing field so as not to disadvantage more enlightened and progressive companies
The huge responsibility of food manufacturers in contributing to the epidemic of cardiovascular disease must be acknowledged, and prevention implemented through food reformulation and effective voluntary, market intervention, or mandatory action throughout the industry.19 Civil society, governments, academia, and health organisations all have a part to play. Denial and procrastination will be costly in terms of both avoidable illness and expenses.
Cite this as: BMJ 2011;343:d4995
We thank Robert Beaglehole and the reviewers for helpful and constructive comments.
Contributors: FPC prepared an Expert Opinion paper presented to NICE, took part in discussions, and drafted the manuscript. SC, PL, and KMcP all contributed to the discussions and made substantial contributions to the draft manuscript. FPC acts as guarantor.
Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years. No other relationships or activities that could appear to have influenced the submitted work, apart from FPC who is unpaid member of CASH, WASH, unpaid technical adviser to WHO and PAHO, individual member of the National Heart Forum and member of the executive committee and trustee of the British Hypertension Society; SC who is a trustee of the Heart of Mersey, and PL, KM, and SC who are chief executive, chair, and trustee, respectively, of the UK National Heart Forum. All the authors were members of the NICE cardiovascular disease population prevention guideline development group. This paper does not necessarily reflect the views of NICE nor does it represent the decisions or the stated policy of WHO and the designations employed and the presentation of material do not imply the expression of any opinion on the part of WHO.
Provenance and peer review: Commissioned, externally peer reviewed.