Fundamentals of Human Nutrition
Potassium

9.3 Potassium

Potassium is an essential mineral found inside the cells of our bodies. It is important for the proper function of all body cells, tissues, and organs. Specific roles include nerve function, blood pressure regulation, and muscle control (Potassium, n.d.). It is also an electrolyte, a substance that conducts electricity. Potassium levels are controlled by the kidneys and come from many different sources including banana and tomatoes (Micronutrient Information Center, n.d.).

9.3.1 Sources

Potassium can be found in a variety of vegetables, fruits, legumes, and meats. For example, foods with high levels (300 milligrams or higher) of potassium include baked potatoes with skin, dried plums, lima beans, yogurt, nonfat milk, chicken, canned tuna, and spinach (Micronutrient Information Center, n.d.). Foods with moderate levels (100-300 milligrams) of potassium include apples, peaches, lamb, broccoli, beets, ham, strawberries, and peas. Foods with less than 100 milligrams of potassium are bread, pasta, eggs, blueberries, bacon, corn, and black olives (Potassium and the Diet, n.d.).

9.3.2 Functions

Potassium function includes blood pressure regulation, muscle control, nerve impulse function, heart function, and electrolyte regulation. Its primary role is to regulate mineral and water balance throughout the body (Potassium and the Diet, n.d.).

Potassium works with sodium to maintain a person’s blood pressure. As sodium accumulates in the blood, the body holds onto water to dilute the sodium (Health Risks and Diseases, n.d.). This increases the amount of fluid around the cells and the volume of the blood in the bloodstream. The increased volume forces the heart to work harder and the pressure can harden blood vessels, leading to high blood pressure and cardiovascular diseases. Potassium have the opposite effect on blood vessels. High potassium levels can relax blood vessel and excrete sodium, which both lowers blood pressure (Health Risks and Diseases, n.d.).

Potassium plays a role in nerve conduction, specifically through the sodium-potassium pump. The sodium-potassium pump works to move three sodium ions out of the cell, while moving two potassium ions into the cell. There is a lower concentration of potassium ions outside the cell and a lower concentration of sodium ions inside the cell. Since the process requires active transport, the ions are moved across a membrane and against their concentration gradients; energy derived from ATP during cellular respiration is required (Nave, n.d.).

In nerve cells, the generation of an action potential is required to transmit electrical signals. The action potential is brought about by changes in the penetrability of the axon cell to sodium and potassium. The channels that allow sodium and potassium to pass through are voltage-gated. The channels remain closed when the cell membrane is at resting potential. An electric current can stimulate the channels to open, allowing sodium to flow in. Sodium ions flow inside in large quantities causing the charge on the inside of the cell to become more positive and results in depolarization. The sodium voltage-gated channels then close and the potassium ion channels open. Potassium moves out of the axon cell allowing the charge on the inside of the cell to become more negative, resulting in the repolarization of the cell. The sodium-potassium pump moves ions in either direction continuously so that many action potentials can be generated (Jones, Fosbery, Gregory, & Taylor, 2013, p. 319).

Potassium also functions to maintain pH levels. Sometimes, an individual can enter an alkalotic state where there is excess of base in the body fluids or tissues that can in turn produce weakness or cramps. The amount of hydrogen in the extracellular fluid is low during alkalosis, so the cells will release hydrogen to increase acidity. As a result, blood serum potassium is absorbed and its level drops. Overall potassium levels are stable, but it is the serum potassium that is affected. Should the level of serum potassium drop below 3.5 mEq/L, the individual is expected to exhibit symptoms of hypokalemia derived from the initial alkalotic condition (Vroman, 2011).

Potassium can help regulate water retention as well. An individual may develop edema, a condition where watery fluid accumulates in tissues and cavities throughout the body causing it to swell. Excess water is most commonly stored around the legs, feet, and ankles. Edema can be caused by overindulging in sodium. Potassium is able to combat sodium’s effects since consuming more potassium causes sodium to be removed from the body through urine. Even though potassium can reduce water retention, excess potassium in the blood can also be detrimental to an individual’s health (McNight, 2015).

9.3.3 Requirements

The adequate intake (AI) levels for potassium established by the Food and Nutrition Board of the Institute of Medicine is categorized by age and sex (Micronutrient Information Center, n.d.). For infants between ages 0–6 months, the recommended AI levels for potassium is 400 milligrams (mg) for both males and females. For children between 1–3 years old, 3,000 mg is adequate for both males and females. For children between ages 4–8, the AI is 3,800 mg. For children between ages 9–13, 4,500 mg is adequate. Adolescents between 14 years old and older for both male and female need about 4,700 mg (Micronutrient Information Center, n.d.). The difference between male and female is when the female is breast-feeding. The female needs more potassium (5,100 mg) to accommodate for their baby (Potassium and the Diet, n.d.).

9.3.4 Imbalance

Most people get their recommended levels of potassium from their diets. However, potassium imbalances and the consequences of an imbalance can still occur. For example, hypokalemia is a medical term for low levels of potassium with symptoms of muscle cramps, bloating, intestinal paralysis, weakness, nausea, upset stomach, and an irregular heartbeat. Hypokalemia can be life threatening and should be treated by a professional or doctor (Potassium, n.d.). Some causes of low potassium levels include use of diuretics, kidney diseases, metabolic disturbances, or excessive vomiting. The use of diuretics, severe vomiting or diarrhea, alcoholism, laxative abuse, eating disorders, and congestive heart failure are all conditions that increase the risk of hypokalemia (Micronutrient Information Center, n.d.).

References

1. Health Risks and Disease. (n.d.). Retrieved August 31, 2015, from http://www.hsph.harvard.edu/nutritionsource/salt-and-sodium/sodium-health-risks-and-disease/

2. Jones, M., Fosbery, R., Gregory, J., & Taylor, D. (2013). Regulation and control. In Cambridge International AS and A level biology (3rd ed., pp. 314–328). Cambridge: Cambridge University Press.

3. McNight, C. (2015, May 8). The Effects of Potassium on Water Retention. Retrieved December 2, 2015, from http://www.livestrong.com/article/225763-the-effects-of-potassium-on-water-retention/

4. Micronutrient Information Center. (n.d.). Retrieved August 27, 2015, from http://lpi.oregonstate.edu/mic/minerals/potassium

5. Nave, R. (n.d.). The Sodium-Potassium Pump. Retrieved December 2, 2015, from http://hyperphysics.phy-astr.gsu.edu/hbase/biology/nakpump.html

6. Potassium. (n.d.). Retrieved August 27, 2015, from https://umm.edu/health/medical/altmed/supplement/potassium

7. Potassium and the Diet. (n.d.). Retrieved August 27, 2015, from http://www.ext.colostate.edu/pubs/foodnut/09355.html

8. Vroman, R. (2011, January 17). Electrolyte Imbalances | EMSWorld.com. Retrieved December 2, 2015, from http://www.emsworld.com/article/10218948/electrolyte-imbalances