Key Concepts

  • Adequate Intake – 1,500 mg/day (or 3,600 mg of salt)
  • Upper Level Intake – 2,300 mg/day (1 teaspoon of salt)
  • Food sources – processed foods primarily
  • Intake of Sodium for Americans – 3,400 mg/day
  • 75% of intake comes from processed foods; 15% from salt shakers; 10% from natural sodium in foods
  • Sodium has many essential functions in the body but too much can cause a number of health challenges

 

Introduction

Sodium! It’s been demonized for a long time. We are commonly taught that salt is terrible for us and if we consume too much it will surely give us a heart attack, and at the least increase our blood pressure and make us thirsty. In excess, salt has been shown to be a menace for most people, but it is a crucial mineral for the maintenance of life at the proper dose.

Functions

First, let me clear up what typical salt consists of. Salt (sodium chloride) is about 40% sodium and 60% chloride. One gram of salt contributes about 400 mg of sodium. 6 grams of salt equals a teaspoon. And 1 teaspoon of salt contributes about 2300 mg of sodium.

Sodium is the most abundant cation in the extracellular fluid (ECF). Sodium is responsible for resting membrane potential, maintaining blood volume, nerve impulse contraction, and muscle contraction (including cardiac muscle). Absorption of sodium in the small intestine is important in ensuring proper absorption of chloride, amino acids, glucose, and water. In general, when sodium is retained, water is retained, and when sodium is lost, water is also lost.

A cell’s membrane potential is maintained in the cell membrane by ion pumps, including the sodium/potassium pump. It is estimated that 20-40% of resting energy expenditure is spent in the activity of these pumps which are ATP-dependent. The large amount of energy required to maintain these pumps is indicative of sodium’s importance in maintaining life. If cell membrane potential was not tightly controlled then nerve impulse transmission, muscle contraction, and cardiac function would all be negatively affected.

Adequate Intake (AI)

The Food and Nutrition Board at the Institute of Medicine provides an adequate intake (AI) of 1,500 mg/day (or 3,600 mg of salt). The American Heart Association is in agreeance with the set standards.

Upper Intake Level (UL)/Excess/Toxicity

The upper intake level (UL) is set at 2,300 mg/day. This is the amount recommended not be exceeded to ensure adverse effects do not occur, both acute and chronic. Nausea, vomiting, diarrhea, and abdominal cramps could occur if large amounts of salt were consumed in one sitting. Hypernatremia (an elevated serum concentration) could also occur although this is rarely caused by excessive sodium intake.

It is interesting to note that the average intake of sodium for a person in the United States is 3,400 mg per day. This is over two times the AI recommendation. About 75 percent of this sodium is coming from the salt added to processed foods. About 15 percent comes from the salt added during cooking and at the table. And only about 10 percent comes from the natural salt found in foods. (Interesting tangent: it is estimated that reducing sodium content in processed foods could prevent an estimated 100,000 deaths and $24 billion in health care costs in the U.S. each year).

Research on Sodium

Our current guidelines for sodium intake are based on evidence that hypertensive individuals whom restricted their sodium intake had improvements in blood pressure readings. There are a number of studies corroborating this finding. The DASH diet, which is low in sodium and high in potassium and emphasizes fruits, vegetables, whole grains, poultry, fish, nuts, and low-fat dairy products, has proven particularly effective in reducing blood pressure.

Unfortunately, salt appears to have different effects person to person, and these recommendations do not take into consideration salt’s effects on individuals without hypertension. Some individuals are salt-resistant – they have little to no change in blood pressure in response to sodium intake, even at intakes 2-3 times higher than AI levels. Others are salt-sensitive and have significant changes in blood pressure in response to increased dietary intake. In fact, 51 percent of hypertensive individuals are estimated to be salt-sensitive while only 26 percent of individuals with normal blood pressure are estimated to be salt-sensitive. Prospective cohort studies have suggested that salt sensitivity may be an independent risk factor for cardiovascular disease. Tangent: no gene polymorphisms have been identified to play a significant role in salt-sensitivity. Testing for salt sensitivity is not standard in clinical care and there does not appear to be an easy test to determine salt sensitivity.

The DASH diet and low-sodium diets have been shown to reduce blood pressure significantly in those with high blood pressure. In pre-hypertensive patients, the effect does not appear to be as dramatic. And in those with normal blood pressure, some studies show that lowering sodium intake has no effect on blood pressure. Additionally, consuming sodium at levels below 2.3 g/day has been shown to be potentially unsafe in individuals with certain medical conditions including diabetes mellitus, kidney disease, and cardiovascular disease.

What really fascinating to note is that the literature suggests that lowering sodium intake does not actually reduce the risk of all-cause mortality in hypertensive and non-hypertensive individuals. High dietary sodium intake has been shown to be a risk factor for cardiovascular disease and coronary heart disease in some studies but not in others.

Deficiency

Sodium deficiency is called hyponatremia and can lead to headache, thirst, confusion, coma, and death. It can be caused by excessive sweating, vomiting, diarrhea, reduced sodium intake, and diuretic medications.

Food Sources

As I mentioned earlier, most Americans get their sodium through processed foods.

  • Salted Peanuts – 1 oz = 116 mg
  • Corn flakes – 1 cup = 182 mg
  • Whole-wheat bread – 2 slices – 291 mg
  • White Bread – 2 slices = 344 mg
  • Salted Potato Chips – 8 ounces (1 bag) = 1,196 mg

If you do consume processed foods regularly (e.g. fast food, prepared meals, frozen dinners, etc…) I encourage you to look at the sodium content provided. You will quickly realize that you are getting a ton of sodium!

And if you do not eat processed foods, it is pretty difficult to exceed the UL or even AI for sodium.

You may also note that a serving of salted peanuts actually has less salt than a serving of cereal. Usually, one does not think of cereal as being a salty food but salted peanuts sure taste salty. The thing about processed foods is the sodium in them is often masked by additives such as sodium bicarbonate or sodium saccharin. Your tongue’s taste receptors immediately pick up the sodium on the salted peanuts and they taste salty because the salt is on the surface of the peanut. In cereal, the salt is not on the surface and the salt receptors on your tongue do not readily pick it up.

The moral of that is if you added as much salt to the surface of your whole foods as what is contained in processed foods, it would taste terrible. Hence, simply by avoiding processed foods you’re intake of sodium would be lowered tremendously. You can also add salt from a shaker liberally without much concern for overdoing it.

 

References/Resources

http://lpi.oregonstate.edu/mic/minerals/sodium

Nutrition for Health and Healthcare

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3724405/

 

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