Pass the Salt? A Look at Population-Based Sodium Reduction Interventions

September 24, 2010

By Ryan Macht, MS4

Faculty Peer Reviewed

On January 11th, the New York City Health Department announced its plans for the National Salt Reduction Initiative, a public health proposal designed to decrease sodium consumption throughout the country. High levels of dietary sodium have frequently been associated with increased rates of hypertension and adverse cardiovascular events.[1,2] The mean salt intake in the United States is extremely high in all age groups and well above the current recommendations of 5.8 g (2300 mg sodium) for those under 40 and 3.8 g (1500 mg sodium) for older adults and those with hypertension.[3] Around 75-80% of this sodium intake is from processed foods, with much less from the salt added when cooking or seasoning at the table.[3] The goal of the initiative is to improve cardiovascular health by reducing the amount of salt in packaged and restaurant foods by 25% over five years, which would in turn reduce the nation’s salt intake by an estimated 20%.[4]

The plan consists of specific targets of sodium reduction for 61 categories of packaged food and 25 classes of restaurant food.[5,6] However, these targets would be completely voluntary, only aimed at “quick service” restaurants, and based on the companies’ overall portfolio of food, not individual products. For instance, if a company made two types of equally popular chips, it would be able to keep a saltier variety as long as the average sodium content of both chips was under the target goal. There is no punishment for not reaching the target goals, but companies and restaurants that are successful will be publicly recognized.[4]

This initiative has generated a significant amount of controversy since being announced. A recent post on the New York Times “Room for Debate” blog highlighted the reactions to the proposed plan from a variety of people including a physician, nutritionist, food critic, public policy advocate, and chef.[7] Most of the opposition is focused on the effect it will have on the taste of food, the ethics of government control of what we eat, and how effective the plan will be in reducing clinically significant disease.

The physiology of how salt intake contributes to hypertension is likely multifactorial. One possible mechanism involves the kidney’s decreased functioning with age, which leads to an inability to excrete excess salt, greater plasma volume, and higher blood pressure.[8] Another hypothesis is that a combination of excess sodium and insufficient potassium intake adversely affects vascular smooth muscle cells, which in turn causes reduced vascular elasticity and higher blood pressure.[8] Regardless of the mechanism, high dietary salt has been found to be strongly associated with hypertension and cardiovascular disease, and may also be associated (independent of its effect on blood pressure) with an increased incidence of stroke, left ventricular hypertrophy, renal disease, stomach cancer, renal stones, osteoporosis, and obesity.[9]

A recent study in the New England Journal of Medicine used a computer model to quantify the estimated effect of a population-wide reduction in dietary salt.[10] The authors found that a reduction of 3 grams per day would decrease the annual number of new cases of coronary disease by 60,000 to 120,000, stroke by 32,000 to 66,000, myocardial infarction by 54,000 to 99,000, and the annual number of deaths from any cause by 44,000 to 92,000.[10] Additionally, they reported that even a modest decrease of salt by 1 gram per day would have a substantial reduction in cardiovascular events and deaths. Finally, they estimated that a 3-gram-per-day reduction would produce 194,000 to 392,000 quality-adjusted life-years (QALYs) and save $10 billion to $24 billion in health care costs, indicating that a decrease in salt intake would be very cost effective.[10]

The proposal by the National Salt Reduction Initiative was largely modeled after plans already implemented in other countries and most closely resembles the United Kingdom model. The strategy has been successful in the UK, where since 2003, sodium levels in many processed foods have voluntarily been reduced by 20-30%.[9] Before and after the initiative was in place, the average salt intake of the UK population was estimated using 24-hour urine collections from random samples. They found that salt intake decreased from an average of 9.5 g/day in 2003 to 8.6 g/day in 2008.[11] However, another research group has criticized this study on the grounds that this estimated reduction is based on a normal variation in a relatively narrow and unchanging range of urinary sodium excretion measured in the UK between 1983 and 2008.[12] They argue that sodium is under strict homeostatic control and human salt intake is set within a physiologic range that is unlikely to be altered by public-policy initiatives.[12]

Some of the most compelling evidence for a population-based salt-reducing intervention comes from Finland. As early as the late 1970s, Finland became one of the first countries to institute public health strategies to reduce salt consumption. By 2002, salt intake had decreased by 40%, diastolic blood pressure had decreased by more than 10 mm Hg, and mortality from stroke and coronary heart disease had decreased by 75% to 80%.[13] These changes are largely attributed to the reduction in salt intake, because other risk factors such as obesity and alcohol consumption increased over the same period.[13]

Cardiovascular disease is the leading cause of death in the United States, and hypertension is an important risk factor that accounts for nearly two-thirds of all strokes and half of all ischemic heart disease.[8] Population-based approaches to reducing salt intake represent a relatively new approach to combating hypertension. It is thought that these initiatives can have profound effects on disease reduction, although their feasibility, ethics, and long-term efficacy are all still strongly debated.

Commentary by Dr. Andrew Wallach

Ryan Macht succinctly summarizes the current debate surrounding the recently announced plan by the New York City Department of Health and Mental Hygiene (NYC DOHMH) to restrict sodium content of processed foods–the source of nearly three-quarters of daily sodium intake in the United States.  This plan, similar in scope to the NYC DOHMH’s plan to restrict trans fatty acids and increase consumption of fruits and vegetables and its ban on smoking in restaurants and bars, seeks to address pressing public health issues at the population level.  In doing so, the probability of success and improved health outcomes is greatly improved.  In the current environment of health care reform, which has focused primarily on insurance and financial issues, it is refreshing to see the government re-focus its efforts on prevention measures.  However, how the ethical debate of big government dictating our diet plays out is yet to be seen.

Ryan Macht is a fourth-year medical student at NYU School of Medicine

Andrew Wallach, MD is a Clinical Assistant Professor, Department of Medicine at NYU School of Medicine

Image courtesy of Wikimedia Commons.

References:

1. Intersalt Cooperative Research Group. Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. BMJ. 1988;297(6644):319-328.  http://www.bmj.com/content/297/6644/319.abstract

2. He FJ, MacGregor GA. Effect of modest salt reduction of blood pressure: a meta-analysis of randomized trials. Implications for public health. J Hum Hypertens. 2002;16(11):761-770.

3. Appel L, Anderson C. Compelling evidence for public health action to reduce salt intake. N Engl J Med. 2010;362(7):650-652.  http://www.nejm.org/doi/full/10.1056/NEJMe0910352

4. Health Department announces proposed targets for voluntary salt reduction in packaged and restaurant foods [news release].   New York, NY: New York City Department of Health and Mental Hygiene; January 11, 2010.  http://www.nyc.gov/html/doh/html/pr2010/pr002-10.shtml.  Accessed January 26, 2010.  http://www.nyc.gov/html/doh/html/pr2010/pr002-10.shtml

5. National Salt Reduction Initiative packaged food categories and proposed targets.  New York City Department of Health and Mental Hygiene web site.  http://www.nyc.gov/html/doh/downloads/pdf/cardio/cardio-salt-packagedfood-targets.pdf. Accessed January 26, 2010.

6. National Salt Reduction Initiative Restaurant categories and proposed targets. New York City Department of Health and Mental Hygiene web site.  http://www.nyc.gov/html/doh/downloads/pdf/cardio/cardio-salt-restaurantfood-targets.pdf. Accessed January 26, 2010.

7. Kurlansky M, Willett W, Kimball C, Sheraton M, Jacobson MF, Kazaks A, Earl R.  Big Brother and the salt shaker. NYTimes.com Room for Debate blog. January 14, 2010.  http://roomfordebate.blogs.nytimes.com/2010/01/14/big-brother-and-the-salt-shaker/?emc=eta1. Accessed January 26, 2010.

8. Mohan S, Campbell NR. Salt and high blood pressure. Clin Sci (Lond). 2009;117(1):1-11.  http://www.ncbi.nlm.nih.gov/pubmed/19476440

9. He FJ, MacGregor GA. A comprehensive review on salt and health and current experience of worldwide salt reduction programmes. J Hum Hypertens. 2009;23(6):363-384.  http://www.nature.com/jhh/journal/v23/n6/full/jhh2008144a.html

10. Bibbins-Domingo K, Chertow GM, Coxson PG, et al. Projected effect of dietary salt reductions on future cardiovascular disease. New Engl J Med. 2010;362(7):590-599.  http://www.nejm.org/doi/full/10.1056/NEJMoa0907355

11. Food Standards Agency. An assessment of dietary sodium levels among adults (aged 19-64) in the UK general population in 2008, based on analysis of dietary sodium in 24 hour urine samples. June 2008. National Centre for Social Research.  http://www.food.gov.uk/multimedia/pdfs/08sodiumreport.pdf.  Accessed January 26, 2010.

12. McCarron D, Geerling JC, Kazaks AG, Stern JS. Can dietary sodium intake be modified by public policy? Clin J Am Soc Nephrol. 2009;4(11):1878-1882.  http://cjasn.asnjournals.org/cgi/content/full/4/11/1878

13. Karppanen H, Mervaala E. Sodium intake and hypertension. Prog Cardiovasc Dis. 2006;49(2):59-75.  http://www.ncbi.nlm.nih.gov/pubmed/17046432

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