Nutrition Basics: Sodium and Chloride (aka, Salt)

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People often use the terms sodium and salt interchangeably. However, they are not the same thing and the misnomer causes confusion (at best) and health problems (at worst).

Salt is a molecule made of ~40% sodium and ~60% chloride. This distinction is important because sodium and chloride have some distinct functions in the body. As well, the “problem” of “too much salt” in our diets is technically too much sodium and has nothing to do with chloride. (Not to mention there is some discussion yet to be had about the impact sodium is having to our health; more on that below.)

Functions in the Body

Sodium and chloride are critical for proper functioning of the body. Without them, we would die.

Sodium’s primary job in the body is fluid regulation. Think of sodium and water as being best friends that go everywhere together holding hands. If you eat a bunch of salty potato chips and your fingers or ankles feel swollen the next day, it’s because the excess sodium held onto extra water. (More about this below in the Symptoms of Toxicity section.)

Just as potassium is the primary cation inside the cell, sodium is the primary cation outside the cell. The balance of potassium and sodium on either side of the cell membranes allows nerve impulse transmission and muscle contraction, including proper cardiac function.

Absorption of sodium in the small intestine and reabsorption in the kidneys is also linked to the absorption of chloride, amino acids, glucose, and water (remember, they are best friends).

Chloride is the second most abundant electrolyte outside the cell (i.e., in the extracellular fluid). However, it is an anion, meaning it has a negative charge in water. (The positive charge of sodium and the negative charge of chloride is the reason they stick together so easily.) As such, it helps to maintain a neutral charge in the extracellular fluid.

Chloride also functions as a:

  • Catalyst of protein digestion in the form of hydrochloric acid in the stomach,
  • Component of the “poison” used by white blood cells to destroy invaders, and
  • Player in helping red blood cells carry carbon dioxide from the tissues to the lungs so it can be exhaled.

Causes of deficiency

Deficiency of sodium and chloride rarely occurs as a result of insufficient intake. Most of the time, deficiency occurs in situations where there is excessive water loss such as:

  • Severe diarrhea,
  • Severe vomiting, and
  • Excessive sweating (as would occur in endurance events, especially in hot and humid environments).

Apparent deficiency of sodium may also occur with excessive water intake. You may have heard of situations where an endurance athlete chooses to drink plain water (i.e., without electrolytes) and ends up with hyponatremia, which is low serum sodium. This occurs because they are losing sodium in the sweat without replacing it while continuing to dilute the sodium that remains in the blood.

Symptoms of deficiency

Symptoms of sodium deficiency include muscle cramps (as happens with magnesium and potassium deficiency also), nausea, vomiting, dizziness, loss of appetite, muscle atrophy, shock and coma. In children, you may also notice a lack of growth.

With severe chloride deficiency, convulsions are the most common indicator, although symptoms of chloride inadequacy include heartburn due to hypochlorhydria (inadequate production of stomach acid). In infants, you may also see loss of appetite, failure to thrive, weakness, lethargy and severely low levels of blood potassium.

Causes of toxicity

The causes of toxicity include excessive intake, inadequate water intake and kidney dysfunction.

Above I mentioned that the body will hold onto extra water when sodium intake is excessive. Remember, they are best friends. Under normal circumstances, the kidneys will eventually filter out the extra sodium and water so that both return to a normal level within the body. However, if the kidneys are not functioning properly, they may not perform this task to a sufficient level. The result may be that the kidneys excrete excess water, but not enough sodium which can lead to hypernatremia (i.e., too much sodium in the blood).

Symptoms of toxicity

The friendship between sodium and water is crucial to our health because it keeps us from drying up and crumbling in a pile of dust. However, it’s also the reason that excess sodium intake may cause increased blood pressure in some people and may be dangerous for someone with heart failure. In those who are considered “salt sensitive”, the extra sodium holds onto extra water for an extended period of time which causes the blood vessels to be filled up with fluid. The result is that the heart has to work harder to move the extra fluid through the completely filled blood vessels. (Think of this like a water hose that is turned on high. The hose becomes really taut and the excess volume is harder to move through the hose.)

I use “may” above because many studies have failed to show a connection between high sodium intake and increased blood pressure. In fact, research which has significantly reduced sodium intake (including the infamous DASH study) has only lowered blood pressure by ~1 point… in other words, not enough to change someone’s hypertension status.

As well, high blood pressure may be caused by insufficient intake of potassium, magnesium, calcium and/or omega-3 fatty acids rather than being caused by too much sodium. (Note: I am in no way discounting the role sodium plays in blood pressure. Rather I want to draw attention to the conclusions of the research and to other factors that may contribute to high blood pressure / hypertension.)

Besides blood pressure changes, symptoms of hypernatremia include edema (swelling especially in the hands and feet), rapid heart rate, difficulty breathing, convulsions, coma, and death.

If there is significant fluid loss with excess sodium intake or inadequate sodium excretion, symptoms may include dizziness or fainting, low blood pressure (because it’s the excess fluid that causes increased blood pressure, not the sodium itself), and diminished urine production (because the body is holding onto water to try and balance how much sodium is present).

There are no known symptoms of chloride toxicity specifically.

Measuring levels

As mentioned, sodium’s primary role in the body is fluid regulation and chloride is found primarily in the blood. As such, abnormal serum sodium and/or chloride levels are typically an indicator of hydration status. Low levels usually indicate over hydration or over retention of water; high levels indicate dehydration or excessive loss of water.

The amount of sodium in the urine is an indicator of sodium intake because the body maintains serum sodium within a small range and any excess is excreted. Of course, this method does not work if kidney function is compromised.

Sources of sodium and chloride

Although many foods naturally have very small amounts of sodium, the two biggest sources of sodium in our diets are salt and processed foods.

While salt has been victimized as the cause of our heart issues because of its sodium content, the fact is that 75% of the sodium in Americans’ diets comes from processed foods because it is used in various forms as a preservative, such as sodium acetate and sodium benzoate. Perhaps more surprisingly, the #1 source of sodium for most people is grain products like bread, crackers, pastries and cookies. It’s not because the amount of sodium used in these products is so much more than in other processed foods (i.e, those foods that require a Nutrition Facts label), but rather because our diets include so many grain-based options. After all, it wouldn’t be completely unheard of for a person to eat cereal for breakfast, a sandwich for lunch, crackers with cheese for a snack and pasta for dinner.

Hint: Read the Nutrition Facts label of every food you purchase. Start to notice how much sodium is in each of the foods you eat and feed your families.

As mentioned above, salt (NaCl) is a compound made of ~40% sodium (scientific element Na) and ~60% chloride (scientific element Cl). This is important because many people are told to reduce their salt intake, when really the goal is to reduce their sodium intake. Since salt added in cooking and at the table only accounts for ~15% of the sodium we consume, many people feel like they don’t get too much salt… when in reality they get tons of sodium from processed foods.

If you are someone who is “salt sensitive” (another misnomer) and you need to reduce your sodium intake (see the section above on toxicity), it is important to consider that most of your sodium is likely coming from processed foods and not from salt or natural foods.

Salt can be mined from the earth (which theoretically is there because of some sea that dried up at some point in the history of our phenomenal planet) or collected from what is left after all the water evaporates from sea water. Sea salt is slightly better for you than table salt because sea salt contains other trace elements that naturally occur in sea water. These may make up to 15% of the volume of sea salt (meaning the amount of sodium is lower for the same amount of sea salt as compared to the same amount of table salt) and include iodine, magnesium, calcium, potassium, selenium, copper, iron, zinc, manganese, and chromium, depending on where the salt came from. As well, sea salt has not been bleached and filtered the way regular table salt has been. And table salt has anti-caking additives, which can make up 2% of the salt.

The remainder of the sodium in our diets occurs naturally in foods. Of course, sea vegetables (like kelp) have a lot of salt because they absorb it from the ocean. However, beets, potatoes, carrots, leafy greens, celery, peanuts, garbanzo beans (chickpeas), mung beans and lots of other plant foods have small to moderate amounts of sodium in them as well.

Besides salt, natural sources of chloride include salt substitutes (which are potassium chloride rather than sodium chloride), seaweed, rye, tomatoes, lettuce, celery, olives, and lots of other vegetables which contain train amounts.

 

Sources:
— Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. 6th ed. Belmont, CA: Wadsworth Cengage Learning; 2013.
— Harrison C. Sea Salt vs. Table Salt – The Truth. Accessed on April 28, 2105.
— Institute of Medicine (US) Committee on Strategies to Reduce Sodium Intake. Henney JE, Taylor CL, Boon CS, editors. Strategies to Reduce Sodium Intake in the United States. Washington (DC): National Academies Press (US); 2010.
— Linus Pauling Institute. Sodium (Chloride). In Micronutrient Information Center. Accessed on April 28, 2015.
— Moyer MW. It’s time to end the war on salt. Scientific American. Accessed on April 28, 2105.
— National Center for Chronic Disease Prevention and Health Promotion, Division for Heart Disease and Stroke Prevention. Get the Facts: Sodium’s Role in Processed Food. Accessed on April 28, 2015.
— U.S. National Library of Medicine. Chloride in diet. In Medical Encyclopedia. February 2, 2015. Accessed on April 7, 2016.

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