Heart Health Controversy: Reducing Sodium Intake

rethink sodium restrictions For years, consumers have been advised to reduce their intake of sodium. The thinking was that sodium increases blood pressure which, in turn, elevates risk for heart disease. This led to the current Dietary Guidelines for Americans’ (DGAs) recommendation to reduce sodium consumption to less than 2,300 mg/day for those between the ages of 2 and 50 years and even lower, to less than 1,500 mg/day, for African Americans, those over 50 years and people with hypertension, diabetes or chronic kidney disease.1  

Needless to say, compliance with such strict sodium recommendations is very poor. Current consumption remains at about 3,500 milligrams per day in the U.S. and in developed countries around the world.2 Even in clinical situations, such as in chronic kidney disease, diets with sodium levels of <2,300 mg/day are extremely hard to follow unless a hospital cafeteria is providing all meals and snacks.  

The science behind salt

Beyond issues of feasibility and compliance, data is accumulating that calls into question the appropriateness of low sodium recommendations. For example, there is now evidence that low sodium intakes may do more harm than good for some individuals. 

A group of studies indicate that low-sodium diets increase risk for heart disease, and that the most beneficial intake is 3,000-5,000 mg/day, or what people are typically consuming.3,4 Another recent study, which tracked more than 100,000 people from 17 countries over an average of more than three years, found that those who consumed < 3,000 mg/day of sodium had a 27% higher risk of death or a serious event such as a heart attack or stroke than those whose intake was 3,000–6,000 mg/day.5  
Very little evidence is available to extend these recommendations to children, yet they are held to the same levels as adults under the assumption that elevated blood pressure starts in childhood.6 In a recent longitudinal study in 2,379 adolescent girls, researchers found that sodium intake was unrelated to blood pressure over a 10-year period, but potassium intake was inversely related.7

To address the disconnect between the newer sodium research and current sodium recommendations, the Institute of Medicine (IOM) convened an expert panel on the topic in 2013, resulting in a report that concluded that that there was insufficient evidence to support the current DGAs for dietary sodium.2 

Further, the report found no evidence to support treating some population subgroups (e.g., African Americans) differently from the rest of the US population.2 This shift reflects the first in a series of changes necessary to turn the tide on sodium policy. 

Why are sodium recommendations being taken with a grain of salt?

Frustrating as it might seem, there are some valid reasons why the new science does not validate the current sodium recommendations.

  • salt on In spite of the dogma that “less sodium is better,” many studies have shown a U- or J-shaped curve for sodium and risk of heart disease. In other words, at very high AND very low sodium intakes, the risk of heart disease increases. The optimal intake range appears to be between 3,000 and 6,000 mg/day, interestingly about what the average American consumes.3,4,8,9 
  • Additional factors are now being seen as instrumental in the sodium-blood pressure relationship that were not recognized in the past. For example, potassium intakes may lower blood pressure.4,6,7  Body mass index, physical activity levels, smoking and alcohol are additional mitigating factors.  Further, the real problem may not be excess sodium but the lack of fruits, vegetables, dairy foods and physical activity.
  • The public health sodium recommendation neglects to take individual variation into account. Often, people are labeled “salt sensitive” if their blood pressure increases with higher salt intake.10 Only about one-third of our population is considered salt-sensitive; the other two-thirds are salt-resistant and do not react significantly to dietary sodium. Still, the recommendation is to restrict sodium across the population, in spite of the fact that low sodium diets may be harmful, linked to a higher risk of death, stroke or heart attack.
  • Emerging research suggests that sodium intake is regulated by our brains—that there are various stimulatory and inhibitory regulators acting on the brain controlling sodium appetite.11 So, when sodium levels are low, aldosterone-sensitive neurons are activated to increase sodium intake.12
  • Supporting this “neuro regulation” theory, sodium intake across 45 countries and spanning five decades has remained amazingly constant between 2,600 and 4,800 mg/day, indicating that intakes are determined by physiologic needs.13 Additionally, in countries like the UK where the sodium content of many foods have been reduced by 25-30 percent, sodium consumption decreases less than 10 percent, which means either people are consuming more food or they are selecting foods that are higher in sodium.14

Coping with controversy

As health professionals, just like in any other field, it is important to acknowledge that politics can get in the way of effective decision-making. Well-meaning groups, individuals following agendas and old paradigms can influence committees to formulate policies that don’t align with the scientific facts.

In addition, the body of science has to reach “critical mass” before policy changes are made, which is actually a good thing. Viewing policy—e.g. the DGAs—as a cruise liner, it cannot be changed like a speed boat, by a simple correction of the steering wheel. It needs to be done little by little, slowly over time. It may be frustrating in the interim, but the resulting policy will be less confusing to consumers who become exasperated when recommendations flip flop.

Until the recommendations catch up with the science, health professionals need to individualize, individualize, individualize. Acknowledge that the DGAs are a starting point for the public, and were never intended to be rigidly adopted by the individual. 

Ask about family history; assess body weight; examine other lifestyle factors; consider taste, culture, tradition, preferences … and then make recommendations that are feasible, realistic and appropriate for each individual client and patient.

After all, isn’t that what health professionals are trained to do?

Lori Hoolihan, Ph.D., R.D.N. 

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References

1http://www.health.gov/dietaryguidelines/dga2010/dietaryguidelines2010.pdf 
2Institute of Medicine. Sodium Intake in Populations: Assessment of Evidence.  2013. National Academies Press: Washington, DC, 2013.
3Graudal N, Jurgens G, Baslund B, Alderman MH. Compared With Usual Sodium Intake, Low- and Excessive-Sodium Diets Are Associated With Increased Mortality: A Meta-Analysis. Am J Hypertens 2014.
4O'Donnell M, Mente A, Rangarajan S et al. Urinary sodium and potassium excretion, mortality, and cardiovascular events. N Engl J Med 2014.
5Mente A, O'Donnell MJ, Rangarajan S et al. Association of urinary sodium and potassium excretion with blood pressure. N Engl J Med 2014.
6National High Blood Pressure Education Program Working Group. The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. Pediatrics 2004.
7Buendia et al. Longitudinal effects of dietary sodium and potassium on adolescent blood pressure. JAMA Ped 2015.
8Pfister et al. Estimated urinary sodium excretion and risk of heart failure in men and women in the EPIC-Norfolk study. Eur J Heart Failure 2014.
9Ekinci et al. Dietary salt intake and mortality in patients with type 2 diabetes. Diabetes Care 2011.
10Franco et al. Salt sensitivity, a determinant of blood pressure, cardiovascular disease and survival. J Am Coll Nutr 2006.
11Geerling,JC, Loewy AD. Central regulation of sodium appetite. Exp Physiol 2008.
12Geerling et al. Aldosterone target neurons in the nucleus tractus solitarius drive sodium appetite. J Neurosci 2006.
13McCarron et al. Normal range of human dietary sodium intake: a perspective based on 24-hour urinary sodium excretion worldwide. Am J Hyper 2013. 
14McCarron et al. Can Dietary Sodium Intake Be Modified by Public Policy? Clin J Am Soc Nephrol 2009.