11.6 – Potassium (Again)
Learning Objective
- Discuss the roles of potassium in the body
- List food groups that are dietary sources of potassium.
Potassium is the most abundant positively charged ion inside of cells. Ninety percent of potassium exists in the intracellular (inside the cell) fluid, with about 10 percent in the extracellular fluid (outside the cells), and only 1 percent in blood plasma. As with sodium, potassium levels in the blood are strictly regulated. The hormone aldosterone is what primarily controls potassium levels, but other hormones (such as insulin) also play a role. When potassium levels in the blood increase, the adrenal glands release aldosterone. The aldosterone acts on the kidneys, where it stimulates an increase in the number of sodium-potassium pumps. Sodium is then reabsorbed and more potassium is excreted. Because potassium is required for maintaining sodium levels, and hence fluid balance, about 200 milligrams of potassium are lost from the body every day.
Other Functions of Potassium in the Body
Potassium plays an important role in managing blood pressure. Potassium balances the effects of sodium on blood pressure because the more potassium you eat, the more sodium you lose through urine. Nerve impulses also involve both sodium and potassium. A nerve impulse moves along a nerve via the movement of sodium ions into the cell. To end the impulse, potassium ions rush out of the nerve cell, thereby decreasing the positive charge inside the nerve cell. This diminishes the stimulus. To restore the original concentrations of ions between the intracellular and extracellular fluid, the sodium-potassium pump transfers sodium ions out in exchange for potassium ions in. On completion of the restored ion concentrations, a nerve cell is now ready to receive the next impulse. Similarly, in muscle cells, potassium is involved in restoring the normal membrane potential and ending the muscle contraction. Potassium also is involved in making proteins, energy metabolism, and platelet function, and acts as a buffer in blood, playing a role in acid-base balance.
Imbalances of Potassium
Insufficient potassium levels in the body (hypokalemia) can be caused by a low dietary intake of potassium or by high sodium intakes, but more commonly it results from medications that increase water excretion, mainly diuretics. The signs and symptoms of hypokalemia are related to the functions of potassium in nerve cells and consequently skeletal and smooth-muscle contraction. The signs and symptoms include muscle weakness and cramps, respiratory distress, and constipation. Severe potassium depletion can cause the heart to have abnormal contractions and can even be fatal. High levels of potassium in the blood, or hyperkalemia, also affects the heart. It is a silent condition as it often displays no signs or symptoms. Extremely high levels of potassium in the blood disrupt the electrical impulses that stimulate the heart and can cause the heart to stop. Hyperkalemia is usually only seen in those with kidney dysfunction.
Needs and Dietary Sources of Potassium
The IOM based their AIs for potassium on the levels associated with a decrease in blood pressure, a reduction in salt sensitivity, and a minimal risk of kidney stones. The AIs for the different age groups are listed in Table 11.6.1.
| Age Group | Milligrams Per Day |
|---|---|
| Infants (0–6 months) | 400 |
| Infants (6–12 months) | 860 |
| Children (1–3 years) | 2,000 |
| Children (4–8 years) | 2,300 |
| Children (9–13 years)* | 2,300-2,500 |
| Adolescents (14–18 years)* | 2,600-3,400 |
| Adults (> 19 years)* | 2,600-3,400 |
*Females: Lower amount Males: Higher amount
Source: Dietary Reference Intakes for Sodium and Potassium. Institute of Medicine. https://www.nap.edu/read/25353/chapter/1 . Accessed May 30, 2019.
Food Sources for Potassium
Fruits and vegetables that contain high amounts of potassium are spinach, lettuce, broccoli, peas, tomatoes, potatoes, bananas, apples, and apricots. Whole grains and seeds, certain fish (such as salmon, cod, and flounder), and meats are also high in potassium. The Dietary Approaches to Stop Hypertension (DASH diet) emphasizes potassium-rich foods. See Chapter 3 for more details on the DASH diet.
Bioavailability
Greater than 90 percent of dietary potassium is absorbed in the small intestine. Although highly bioavailable, potassium is a very soluble mineral and easily lost during cooking and processing of foods. Fresh and frozen foods are better sources of potassium than canned.
Key Takeaways
- Potassium plays an important role in managing blood pressure. Potassium balances the effects of sodium on blood pressure because the more potassium you eat, the more sodium you lose through urine.
- Nerve impulses also involve both sodium and potassium. Similarly, in muscle cells, potassium is involved in restoring the normal membrane potential and ending the muscle contraction.
- Potassium also is involved in making proteins, energy metabolism, and platelet function, and acts as a buffer in blood, playing a role in acid-base balance.
- Fruits and vegetables that contain high amounts of potassium are spinach, lettuce, broccoli, peas, tomatoes, potatoes, bananas, apples, and apricots. Whole grains and seeds, certain fish (such as salmon, cod, and flounder), and meats are also high in potassium.
- The Dietary Approaches to Stop Hypertension (DASH diet) emphasizes potassium-rich foods. See Chapter 3.7 for more details.
Contributors
University of Hawai’i at Mānoa Food Science and Human Nutrition Program: Allison Calabrese, Cheryl Gibby, Billy Meinke, Marie Kainoa Fialkowski Revilla, and Alan Titchenal
