Potassium as a Plant Nutrient
- Arden D. Day
- Kenneth L. Ludeke
Potassium is one of the macronutrients and it is an essential element for plant growth and reproduction. Potassium is usually present in plants in quantities larger than any other nutrient except nitrogen. Some plants and plant tissues accumulate relatively large quantities of potassium. Tobacco (Nicotiana tobacum L.) leaves, for example, may contain as much as 8% potassium on a dry weight basis and they may show symptoms of potassium deficient if the content falls below 3%. Although plants are capable of absorbing relatively large quantities of potassium from soils, a deficiency of potassium in soils is not as widespread as a deficiency of nitrogen. Experience in the midwestern USA has shown that nitrogen may be deficient for a number of years before potassium becomes deficient. Then, within a period of a few years, a definite potassium deficiency may develop. The explanation for this behavior appears to be that many soils originally have a large reserve of potassium, from which potassium may be withdrawn at a rate determined, to a large extent, by the plant. The behavior of potassium in this respect is in contrast to the behavior of nitrogen, because the maximum rate of withdrawal of nitrogen from the soil is largely beyond the control of the plant (Black 1957).
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Every heartbeat, contraction and muscle impulse relies on potassium. The third most-abundant mineral in the human body, potassium is an electrolyte, regulating fluid balance by transferring nutrients and waste in and out of cells.
Awareness of potassium’s role in health has been heightened by its repeated classification by the Dietary Guidelines for Americans as an under-consumed nutrient. Potassium was declared a “nutrient of public health concern” by the 2015 Dietary Guidelines Advisory Committee because research has associated poor health outcomes, including hypertension and cardiovascular diseases, with low intake. It is estimated that less than 3 percent of the U.S. population achieves potassium intake above the Adequate Intake, or AI. Thus, the new Nutrition Facts label will list potassium and the Daily Reference Value will reflect an increase from 3,500 milligrams to 4,700 milligrams for the percent Daily Value.
Roles in Health
Potassium can blunt the effects of dietary sodium and help lower high blood pressure. Reducing hypertension in turn reduces risk of associated diseases such as heart disease, stroke and kidney disease. Highlighting potassium’s health impact, the U.S. Food and Drug Administration authorized the following health claim based on the Food and Drug Administration Modernization Act of 1997: “Diets containing foods that are a good source of potassium and low in sodium may reduce the risk of high blood pressure and stroke.”
Research shows potassium also may play a role in decreasing bone loss and reducing risk of kidney stones.
The Dietary Reference Intakes for potassium are under review by a scientific expert panel because of potassium’s perceived impact on chronic disease. The current daily AI is 3,000 milligrams for children 1 to 3; 3,800 milligrams for ages 4 to 8; 4,500 milligrams for ages 9 to 13; 4,700 milligrams for ages 14 and older, including pregnant women; and 5,100 milligrams for lactating women.
These values are based on dietary consumption amounts that were shown to maintain lower blood pressure, reduce risk of kidney stones and possibly minimize bone loss. Excess physical activity, sweating and diarrhea can increase demands for potassium.
Sources of Potassium
Potatoes, beans and many fruits and vegetables contain potassium. While milk and bananas contain some potassium, neither is considered a good source, contrary to popular belief (see chart below for other food sources of potassium).
One of the most-studied evidence-based approaches to helping people consume more potassium is the Dietary Approaches to Stop Hypertension, or DASH diet. For the past eight years, U.S. News & World Report ranked DASH “best overall diet” because it contains low-fat or fat-free dairy, fruits, vegetables, whole grains, fish, poultry, beans, seeds, nuts and vegetable oils. DASH also includes foods that are rich in potassium, dietary fiber and nutrients associated with good health and lower blood pressure.
|1 large baked potato (with skin)||1,644mg||Excellent|
|1 cup canned white beans||1,189mg||Excellent|
|1 cup sweet potato baked (with skin)||950mg||Excellent|
|1 cup acorn squash, cooked||896mg||Good|
|1 cup spinach, cooked||839mg||Good|
|1 cup avocado, cubed||728mg||Good|
|1 ⁄4 cup roasted soybeans||632mg||Good|
|1 cup orange juice||496mg||Good|
Signs of Deficiency
Although low levels of potassium, or hypokalemia, can have serious health consequences, low potassium intake alone rarely causes deficiency in the general, healthy population because kidneys can lower excretion. The most common cause of hypokalemia is excessive losses, including profuse sweating, diarrhea, vomiting and kidney disease. Some diuretics, laxatives, steroids and types of antibiotics also can result in hypokalemia.
Temporary decreases in serum potassium normally are corrected after eating or drinking electrolytes; however, severe deficiency can be serious. Signs may include extreme fatigue, muscle spasms, weakness, cramping and irregular heartbeat.
Populations at Risk
Individuals at risk for hypertension and stroke, including African-Americans, older adults and people with diabetes and kidney disease, may be at risk for potassium deficiency. People with inflammatory bowel disease may have low potassium levels due to increased losses through the intestines.
Potassium is an important nutrient for heart health and the prevention and management of high blood pressure. In addition to recommending mindful sodium consumption, registered dietitian nutritionists should emphasize the importance of potassium for cardiovascular health.The third most-abundant mineral in the human body, potassium is an electrolyte, regulating fluid balance by transferring nutrients and waste in and out of cells. ]]>