Sodium is an essential mineral that we cannot live without. Sodium is what allows our nerves to send electrical signals throughout the body, our muscles to work, and it helps us to control blood pressure and blood volume. As with most things we consume, too much or too little sodium intake can have detrimental effects on the body. Too little sodium in the diet can cause hyponatremia, low blood sodium, which causes our cells to swell up with water to balance the concentration of electrolytes between the blood and inside cells. Hyponatremia can be caused by excessive water intake, excessive sweating, and/or extremely low sodium intake. Despite the high consumption of sodium in the U.S., hyponatremia is surprisingly common, especially in endurance athletes, but is also easily treated if symptoms aren’t ignored (muscle weakness, spasms, nausea, headaches, fatigue, etc.). The opposite problem, hypernatremia, is mostly a result of dehydration rather than excessive sodium intake. In the case of hypernatremia, water is drawn out of cells and into the blood to dilute the high concentration of sodium. Hypernatremia can also be easily treated (Medscape, 2015). However, in the case of chronically high sodium intake, the potential damage that occurs over time may be next to impossible to reverse, which is why it is essential to understand what is going on and how much sodium you are actually consuming on a daily basis.
Proper sodium balance in the body is tightly controlled by several physiologic mechanisms that influence thirst, fluid excretion by the kidneys, and indirectly, sodium intake. No one is perfect, and sodium/water intake is not going to be exactly the same on any two days, but the body is extremely flexible, with many different systems in place to tackle any problem and still maintain its composure. But when you constantly push your body to its limits, the body has to make adjustments and adapt. When it comes to excessive sodium intake, the changes that your body is forced to make are not exactly advantageous. High sodium intake has been linked to elevated blood pressure, and although there are many possible causes for this phenomenon, it is clear that the heart and kidneys play a main role (Farquhar, Edwards, Jurkovitz, & Weintraub, 2015).
Normally, as blood passes through the kidneys and any waste is filtered out, your kidneys are noticing how much water or sodium is in the blood and they also take note of blood volume and pressure. When we become dehydrated, the kidneys sense a high concentration of electrolytes in the blood and decreased blood volume. To combat this problem, less water is excreted in the urine, and most is reabsorbed back into the blood stream. If the blood is too dilute, excess water is excreted, diluting the urine (Stanhewicz & Kenney, 2015). When sodium intake is excessive, the kidneys will retain water in an attempt to dilute the blood. The renin-angiotensin-aldosterone hormone system will also tell the kidney to excrete sodium, but any defects in this system tend to lead to sodium-induced hypertension (Farquhar et al., 2015; Choi, Park, & Ha, 2015). The body is particularly good at retaining sodium, but some evidence suggests that excreting sodium doesn’t work as well from an evolutionary standpoint (our ancestors probably only ate up to 1g of sodium a day) (Choi et al., 2015). Certain populations have evidence of an impaired renin-angiotensin-aldosterone system, such as African Americans, who seem to have an impaired renin response to changes in plasma sodium levels (Farquhar et al., 2015).
Some studies suggest that the increase in extracellular volume—due to water leaving the cells to balance out the sodium concentration and fluid retention by the kidneys—causes an increase in cardiac output, which is a measure of the amount of blood pumped by the heart in a given amount of time. If blood vessels in the periphery don’t decrease resistance to the blood flow, blood pressure increases and the heart has to work harder to pump more volume throughout the body (Farquhar et al., 2015). At this point, a vicious cycle begins as high blood pressure continues to wear out the heart and start causing problems elsewhere, especially at the kidneys. When the kidneys are subject to high blood pressure, proteins, and other precious molecules start leaking into the filtrate and get excreted in the urine. The kidneys, like the heart, have to work harder to keep doing their job well. For someone who already has kidney disease, this can be especially dangerous.
Since the 2010 Dietary Guidelines for Americans came out, it has been recommended that everyone age 2 and up should consume no more than 2,300mg everyday or up to 1,500mg for specific populations (e.g., adults over 51 years old, African Americans, or anyone with high blood pressure, diabetes, or kidney disease) (CDC, 2015). According to Harvard Health, Americans consume an average of 3,266mg of sodium a day (Skerrett, 2012). The Centers for Disease Control and Prevention states that 9 in 10 children in the U.S. eat more sodium than recommended. In addition, 1 in 6 of U.S. children have raised blood pressure, one of many strong risk factors for heart disease and/or stroke (CDC, 2015). It is estimated that reducing sodium intake by 400mg per day, 28,000 deaths could be avoided every year, and we could save $7 billion in healthcare costs alone (Skerrett, 2012). These numbers may seem drastic, but high blood pressure associated with high sodium intake is a leading cause of heart disease (heart attack, stroke, etc.) and kidney failure among many other problems (Skerrett, 2012). The best way to cut down on your sodium intake is to prepare more foods yourself, using only fresh or minimally processed ingredients. For most people, this isn’t always an option, so it is important to understand how much sodium you are consuming on a daily basis and where sodium might be hiding in unexpected places.
The most obvious way that we get sodium is from table salt in the form of sodium chloride (NaCl). To clarify, when someone talks about sodium, they are referring to the mineral Na, whereas salt generally refers to a compound like sodium chloride (NaCl). Just one teaspoon of salt has about 2,300mg of sodium. Less obvious sources of sodium are breads and rolls, pre-cooked/processed foods (like frozen entrees), cheeses, cold cuts/deli meats, poultry, soups, and basically any foods prepared outside the home, just to name a few (Skerrett, 2012). Frozen entrees are particularly dangerous—some brands may not go over 1,000mg of sodium in their products whereas others have meals with over 2,000mg of sodium in just one serving. Harvard Health suggests that despite the overwhelming sodium content of some items like frozen dinners, breads and rolls are the biggest contributors to sodium intake because bread products are consumed so frequently (Skerrett, 2012).6 Two slices of bread may provide about 300mg, whereas a typical plain bagel may have up to 500mg of sodium without any toppings that could easily take your breakfast or lunch up to 1,000mg of sodium (1 small package of cream cheese has about 270mg and 3 slices of deli turkey meat may have 600mg or more).
In order to be aware of your sodium intake, it is essential to read nutrition labels and to also take note of the serving size. In between meals, instead of snacking on chips, crackers, cookies or some other type of packaged good, try to eat fresh fruit, vegetables, or unsalted nuts instead. Choose low-sodium products whenever possible (especially when buying soups or canned foods), and take some time to become familiar with the sodium content of all the different types of products you might eat on a daily or weekly basis. The more you pay attention and learn about your sodium intake, the easier it will be to make better decisions and soon you will be able to effortlessly decrease your sodium consumption. Regardless of your current sodium intake, it’s never too late or too soon to start understanding what you’re putting into your body and how it affects your life.
Centers for Disease Control & Prevention (CDC). 2015. Salt. Retrieved from http://www.cdc.gov/salt/
Choi, H. Y., Park, H. C., & Ha, S. K. 2015, June. Salt Sensitivity and Hypertension: A Paradigm Shift from Kidney Malfunction to Vascular Endothelial Dysfunction. Electrolyte & Blood Pressure, 13(1):7–16.
Farquhar, W. B., Edwards, D. G., Jurkovitz, C. T., & Weintraub, W. S. 2015, March. Dietary Sodium and Health: More Than Just Blood Pressure. Journal of the American College of Cardiology. 65(10):1042–1050.
Medscape. 2015. Drugs and Diseases. Retrieved from http://reference.medscape.com/
Skerrett, P. J. 2012. Everyday Foods Are Top 10 Sources of Sodium. Harvard Health Blog. Retrieved from http://www.health.harvard.edu/blog/everyday-foods-are-top-10-sources-of-sodium-201202084215
Stanhewicz, A. E., & Kenney, W. L. 2015, September. Determinants of Water and Sodium Intake and Output. Nutrition Reviews. 73 Suppl 2:73–82.