Download Potassium and human nutrition: The soil-plant

Karnataka J. Agric. Sci.,24 (1) : (39-44) 2011
Potassium and human nutrition: The soil-plant-human continuum
K. BHASKARACHARY
Food Chemistry Division, National Institute of Nutrition, Hyderabad-500007, India
Email: [email protected]
(Received: November, 2010)
Abstract : Most potassium occurs in the earth's crust as minerals, such as feldspars and clays. Potassium ranks seventh in
order of abundance in the earth's crust. As rocks slowly disintegrate, potassium is released, but the rate of release is too slow
to provide the large amounts of this essential nutrient required by crops. Humans obtain the majority of their potassium either
directly from plants or indirectly through the animal products in their diet. Thus potassium is considered as an indispensable
macro element for sustenance of life on the earth. Starting from soil health which is essential for plant growth and subsequently
the health of animals and humans, potassium has important role to play. The current review covers the various roles
potassium play in soil, plant and human health. In view of the recent interest generated on the new roles of potassium in
human health i.e. control of hyper tension etc., particularly emphasis has been placed on the clinical significance and cellular
functions of this electrolyte in human health and disease.
Key words: Potassium, soil health, animal health, human health, clinical significance
Introduction
resistant to disease attack. Sound fertility management and
fertilization practices provide assurance that stress induced by
K defciency is not a factor in crop production (Cook and Duff,
1976). Several factors influence the effectiveness of K fertilizer
in reducing crop stress and disease incidence. Of all the nutrients
essential for plant growth and function, potassium (K) is most
often associated with reducing disease severity. It should be
recognized, however, that K does not work alone. The healthiest,
most profitable crops are produced with balanced fertility
management practices that minimize nutrient stress throughout
the growing season.
Its presence is of great importance for soil health, plant
growth and animal nutrition. Although it is soluble in water,
little is lost from undisturbed soils because as it is released from
dead plants and animal excrements, it quickly becomes strongly
bound to clay particles, and it is retained ready to be re-adsorbed
by the roots of other plants. As such, the element is required in
relatively large proportions by the growing plant. The
consequences of low potassium levels are apparent in a variety
of symptoms such as restricted growth, reduced flowering, lower
yields and lower quality produce. A high water soluble level of
potassium cause damage to germinating seeds and inhibits the
uptake of other minerals, and reduces the quality of the crop.
Potassium is a major constituent in all living cells and,
potassium (K) is essential nutrient required in large amounts by
plants, animals and humans (Hamdallah, 2004). Most potassium
occurs in the earth’s crust as mineral, such as feldspars and
clays. Potassium ranks seventh in order of abundance in the
earth’s crust. As rocks slowly disintegrate, potassium is released,
but the rate of release is too slow to provide the large amounts
of this essential nutrient required by crops. Humans obtain the
majority of their potassium either directly from plants or indirectly
through the animal products in their diet. Potassium is a key
element for crops / plant growth. Therefore, the intricate
relationship between plant nutrition, animal nutrition and the
impact on food chain for human is very much essential.
Potassium and soil health
Soil may be defined as a thin layer of earth’s crust which
serves as a natural medium for growth of plants. Term, soil, is
used to describe agriculture and garden life. Soil is the principal
attribute and supports life on earth. Soil has four main
components such as minerals, organic matter, air and water. A
fertile soil can be described as it is rich in nutrients necessary
for basic plant nutrition, including nitrogen, phosphorus and
potassium. Among the minerals potassium stands as macro
element and very much essential for plant growth. Heavy crop
production rapidly depletes soils of potassium, and agricultural
fertilizers consume 93% of the potassium chemical production
of the modern world economy. Maintenance of adequate
potassium is therefore, essential for both organic and
conventional crop production.
Disease resistance in crops is genetically controlled.
However, natural disease resistance mechanisms can be
enhanced by plant nutrients. Potassium deficiency symptoms
such as thin cell walls, weakened stalks and stems, smaller and
shorter roots, sugar accumulation in the leaves, and
accumulation of unused nitrogen (N) encourage disease
infection. Each of these reduce the ability of the plant to resist
entry and infection by fungal, bacterial and viral disease
organisms. A healthy plant, free from stress, is much more
Land is the starting point
Because, soils are the natural base for growing crops and
raising animals; then it is imperative that its fertility will impose
the quality and mineral content of such agricultural products.
Therefore, nutrient deficiencies in soils are reflected not only
on crop yields, but also on their contents of mineral nutrients.
Food stuffs and animal feeds, containing low amounts of
nutrients, would lead to mineral deficiencies in animals and
humans also.
There were rare occasions, scientists working on various
disciplines like (soil science/plant nutrition, human nutrition,
veterinary/animal nutrition, as well as, medical sciences and
human nutrition), would convene to study the inter-related
problems and concerns of these domains. Only a multidisciplinary approach to study those areas would produce
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Karnataka J. Agric. Sci.,24 (1) : 2011
the help of potassium as they develop resistance against
drought, variations in temperatures and plant diseases (Nus
and Sandburg, 1991). This element also helps the plant to absorb
more water and improve the health of the plants. Together with
nitrogen and phosphorous, potassium is one of the essential
macro minerals for plant survival.
plausible remedies to the nutrients imbalance and deficiencies
in the human diet, that can be best offset by treating those
deficiencies in plants and consequently in animals and finally
on human population.
Potassium release from soil minerals
The most common mineral sources of K in soils are feldspars
and micas, soil minerals remaining from the primary parent
material. Weathering of these primary minerals produces a range
of secondary minerals that may also serve as a source of
potassium in soil. These minerals include micaceous clays such
as illite and vermiculite. Crushed rocks and minerals have been
evaluated as potassium sources in many field and greenhouse
experiments. In general, plants are able to gain a very limited
amount of potassium from minerals applied as biotite, phlogopite,
muscovite, and nepheline. Feldspar potassium is not plant
available without additional treatment or weathering. The rate
of K release from minerals is influenced by factors such as soil
pH, temperature, moisture, microbial activity, the reactive surface
area, and the type of vegetation. Therefore, a mineral that is
somewhat effective as a K source in one condition may be
ineffective in another environment. Some soil minerals may act
as a sink for removing K from solution. When K is adsorbed in
the interlayer sites of illite, vermiculite and other smectite clays,
the clay layers collapse and trap the K within the mineral lattice.
This fixation process is relatively fast, while the release of this
interlayer K is very slow. Non-exchangeable K should not be
confused with mineral K, since non-exchangeable K is held
between adjacent tetrahedral layers of clay, instead of being
covalently bonded in mineral crystal structures.
Potassium and human health
Potassium, is the third most abundant mineral in human body,
identified as the synonym for health insurer. Potassium is the
principal positively charged ion (cation) in the fluid inside cells,
while sodium is the principal cation in the fluid outside cells. It
is one of the substances found in foods that maintain the body’s
internal balance of fluids and chemicals. More than 98% of the
body’s potassium is intracellular; measuring it from a blood
sample is relatively insensitive, with small fluctuations in the
blood corresponding to very large changes in the total bodily
reservoir of potassium. Potassium is found in especially high
concentrations within plant cells, and in a mixed diet, it is most
highly concentrated in fruits.
It contains qualities for maintaining a high level of human
well-being and a cheerful lifestyle (Heyka, 2009). Apart from
acting as an electrolyte, this mineral is required for keeping heart,
brain, kidney, muscle tissues and other important organs of
human body in good condition. Elevations or deficiencies of
this important mineral can cause problems and, in the extreme,
even death. Maintaining consistent levels of potassium in the
blood and cells is vital to body function. Therefore, there is no
way one should overlook the inclusion of potassium in routine
diet plan (O’Shaughnessy, 2006). The health benefits
of potassium includes blood pressure, anxiety, stress, muscular
strength,
metabolism,
heart
strokes,
kidney
disorders, water balance, electrolytic functions, nervous system
and many other health benefits are well documented (Poirier,
1984; Sacks et al., 1998). Potassium chloride is the main
compound of this mineral amongst others. It works in association
with sodium to perform a number of critical body tasks.
Potassium may be looked upon as an essential health nutrient,
due to following health benefits:
Brain stroke: Potassium plays an important role in keeping
the working of brain in normal state. It is of great importance in
preventing the occurrence of stroke in human brain (Iso et al.,
1999). Though, the exact mechanism of potassium involvement
in brain stoke is not known, Potassium decreases vascular
smooth muscle cell proliferation in the small arteries of the brain
and two-pore domain potassium channel family (K2P channels)
could be shown to be involved in mechanisms contributing to
neuronal damage after cerebral ischemia (Ehling et al., 2010).
Low blood sugar: Decrease in potassium level causes a drop
in blood sugar level. Decrease in blood sugar level causes
sweating, headache, weakness, trembling and nervousness.
Intake of potassium chloride and sodium provides immediate
relief from such situation (Apstein, 1998; Apstein and Opie,
1999).
Muscle disorders: Potassium plays an important role in
regular muscle contraction. Right concentration of potassium,
Potassium balance in soil
Farming always leads to removal of potassium and additional
loss of potassium through leaching and runoff is inevitable, the
potential of a cropping management system to replenish the
potassium reserve is important. The demand for K by various
crops has been well established by measuring the potassium
concentration in the harvested portion of the crop. However,
much less attention has been paid to the rate at which K must be
supplied to growing plants. Both the total amount required
(quantity) and the rate of supply frequency are equally important.
This concept is important for all crop growth, but requires special
attention when using low-solubility nutrient sources that may
provide an adequate amount of total K, but not at a rate
sufficiently rapid to meet peak-demand periods of plant growth.
Potassium and plant growth
Potassium (K) is often described as the “quality nutrient”
for crop production. With a shortage of K, photosynthesis,
respiration, translocation, and a number of enzyme systems don’t
function very well. The result can be a reduction of plant growth
and, often, of crop quality. Its primary function in the plant is its
role in the maintenance of osmotic pressure and cell size, thereby
influencing photosynthesis and energy production as well as
stomata opening and carbon dioxide supply, plant turgor and
translocation of nutrients. Capacity of crops is increase with
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Potassium and human nutrition: The soil-plant-human continuum
is required for the regular contraction and relaxation of the
muscle. Most of the potassium ions of the human body are
present inside the muscle cells. It maintains muscle function
and optimal nerve. A large part of the weakened connective
tissue from a potassium deficiency is manifesting itself by virtue
of the indirect effect a continuing potassium deficiency is having
on the the copper metabolism especially as it pertains to the
copper catalyzed lysyl oxidase enzyme.
Cramps: Muscle cramps result due to low level
of potassium in the blood, a condition called as hypokalemia.
Intake of a banana everyday prevents muscle cramp. Bananas
are rich in potassium content.
Brain function: Potassium channels play a key role in
maintaining the electrical conductivity of brain and affect the
brain function. High levels of extracellular K+ ensure proper
development and prolong survival of cerebellar granule neurons.
It is also involved in higher brain function like memory and
learning. In addition to it, serious ailments like epilepsy are related
to the functioning of potassium channels. When a neuron
decides to transmit signal, the cell wall suddenly becomes
permeable to sodium ions, and sodium ions near the cell wall
suddenly move into the cell, followed a microsecond later by a
flow of thousands of potassium ions in the opposite direction
(Fuhrman, 1967). This change in permeability shoots down the
nerve fiber as a wave at about 100 meters per second powered
by 1/10 of a volt of concentration differential (Baker, 1966).
Blood pressure: Potassium is helpful in reversing the role
of sodium in unbalancing the normal blood pressure (Brancati
et al. 1996; Cappuccio and MacGregor, 1991). Thus, it acts as a
vital component, which maintains the normality of blood
pressure in human body. This further abolishes the possibilities
of heart diseases and hypertension (Burgess et al., 1999;
Pikilidou et al., 2007). Regulation of blood pressure is an
important function of this mineral (Appel, 1999; Houston, 2007).
The mechanism of the antihypertensive effect is not well defined.
Variations in serum potassium within the physiologic range may
directly affect vascular smooth muscle tone. Potassium may
also influence the regulation of blood pressure through effects
on sodium handling, aldosterone secretion, the renin/
angiotensin system, renal kallikrein, eicosanoids, and atrial
natriuretic peptide (Smith et al., 1992). The sodium pump probably
operates at two different sites, one affected by aldosterone, the
other by vasopressin (a protein peptide hormone, used to retain
water by humans), and using a different energy system (Sharp,
1966). The switch to a rheostat that modulates the balance of
salt and potassium in the kidney, thereby raising
or lowering blood pressure. Anxiety and stress: Potassium is of great importance for
people suffering from undesirable mental states like anxiety and
stress. It is considered as a perfect stress buster and thus, it
ensures efficient mental performance of human body.
Muscular strength: This is in fact, one of the most
appreciable benefits of potassium, as it ensures proper growth
of muscle tissues and proper utilization of energy released during
metabolism to add significant worth to muscular strength (Singh
et al. 1999). The muscles, together with cardiac muscle, are prone
to paralysis due to deficiency of potassium in diet (Matsui et
al., 2006; Young et al., 1995). A study conducted on a ninemonth infant, weighing 9.8 kg with hypotonia secondary to acute
hypokalaemia (1.0 mmol/l), muscle strength was improved as
the serum potassium was increased by supplementation (Ried
et al., 1997). Metabolism: It assists in metabolic process of various
nutrients like fats, proteins and carbohydrates. Thus,
potassium is of great value in extracting the energy out of
nutrients consumed by man (Blevins, 1985). In the cytoplasm, K
has an important role in providing the correct ionic environment
for metabolic processes. The ionic requirements of protein
synthesis seem to be particularly important in determining the
composition of the cytoplasm. Potassium is known to be the
activator for several enzyme systems (Suelter, 1970). Since only
minute amounts are needed for most of them, there could never
be a deficiency which would inactivate the majority of them.
Heart and kidney disorders: The health benefits
of potassium ensure good health for heart as well as kidneys
(Kendler, 1997). Several studies suggest that potassium
deficiency can contribute to diastolic dysfunction and possibly
to systolic dysfunction as well. One mechanism by which
potassium might help prevent heart failure is by inhibiting cardiac
NADPH oxidase activity, thereby decreasing oxidative stress.
High salt intake significantly increased blood pressure, impaired
left ventricular relaxation, and increased the activity of IVADPH
oxidase in cardiac tissue. High potassium intake improved left
ventricular relaxation and reversed the elevation of NADPH
oxidase activity, even though blood pressure remained high. It
plays an irreplaceable role in regulating the functions
of potassium. Apart from this, this mineral assists kidneys to
remove waste by the process of excretion (Rafferty and Heaney,
2008). However, it is strictly advisable to consult your doctor to
get recommendation about dosage. Abnormally high calcium in
the urine increases the risk of developing kidney stones.
Increasing dietary potassium intake has been found to decrease
urinary calcium excretion, thereby potentially preventing kidney
stone formation.
Water balance: Potassium has another significant role to
play in maintaining the desirable water balance in human body.
There are different types of cells, which require having
proper water balance for proper functioning and potassium aids
these cells in regulating this balance. Potassium also regulates
the acid-base balance in the blood and tissues. During a
potassium deficiency, potassium migrates out of the cell and
causes the cell fluid to become acidic (lower pH) (Davis, 1970).
This is probably related to the circumstance that sodium does
not take up the full slack, coupled with a rise in weak base
forming anions such as positively charged amino acids. The
buffering action of the negatively charged ions of weak acid
forming anions such as phosphate is the chief innate regulator
of the acid - base balance.
Electrolyte: Potassium plays the significant role as an
electrolyte in human body. It helps in regulating the level of
fluids in human body and thus performs a number of critical
body functions (Matsumura et al., 2000).
Nervous system: Potassium helps in boosting the spirit of
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Karnataka J. Agric. Sci.,24 (1) : 2011
nerve reflexes to transmit message from one body part to another.
This in turn helps in muscle contraction to perform various
activities every day. Rapid changes in extracellular K+
concentration in the mammalian CNS are counteracted by simple
passive diffusion as well as by cellular mechanisms of K+
clearance. Buffering of K+ can occur via glial or neuronal uptake
of K+ ions through transporters or K+-selective channels. A
specialized form of spatial buffering named K+ siphoning takes
place in the vertebrate retina, where glial Muller cells express
inwardly rectifying K+ channels (Kir channels) positioned in
the membrane domains near to the vitreous humor and blood
vessels thereby controlling blood pressure. They suggest a
close physical and functional relationship between Kir and water
channels in glial cells (Koufi and Newman, 2004).
Table 1. High potassium foods (>450 mg per serving)
Food
Measure
Potassium (mg)
Avocados
3 oz.
540
Bananas
1 medium
467
Beets, cooked
1 cup
519
Beet greens, cooked
1 cup
1,309
Broccoli
1 cup
505
Brussels Sprouts, cooked
1 cup
504
Cantaloupe
1 cup
495
Chick Peas, cooked
1 cup
477
Cod
4 oz.
585
Halibut
4 oz.
653
Kidney Beans, cooked
1 cup
713
Lima Beans, cooked
1 cup
955
Lentils, cooked
1 cup
731
Papaya
1 medium
781
Raisins
1/2 cup
544
Soybeans
1 cup
886
Spinach, cooked
1 cup
839
Swiss Chard, cooked
1 cup
961
Trout
4 oz.
500
Tuna
4 oz.
645
White Beans, cooked
1 cup
1,189
Balancing of potassium in body
“Hyperkalemia” is when there is too much potassium in the
blood. Older people are at a greater risk of hyperkalemia because,
as people age, the kidneys are less efficient at eliminating
potassium. Also, many medications associated with the elderly
can affect their potassium levels. Too much potassium in the
blood can cause diarrhea, nausea, vomiting and ulcers. When
there is too little potassium in the blood due to loss through
urination or in the intestines this condition is called
“hypokalemia”. Hypokalemia is rarely caused by not enough
potassium in the diet. Symptoms of hypokalemia are weakness,
fatigue, stomach issues, muscle cramps and irregular heartbeat.
Hypokalemia can become life-threatening, so it is important for
it to be treated by a doctor.
Table 2. Moderately high potassium foods (225 - 450 mg per serving)
Food
Measurement Potassium (mg)
Almonds
2 oz.
412
Carrots, raw
1 cup
394
Celery, raw
1 cup
344
Green beans, cooked
1 cup
374
Kale, cooked
1 cup
296
Kiwi
1 medium
252
Milk, nonfat
1 cup
376
Mustard greens, cooked
1 cup
283
Orange
1 medium
237
Peanuts
2 oz.
374
Salmon
4 oz.
425
Tomato, ripe
1 cup
400
Turnip greens, cooked
1 cup
292
Symptoms of deficiency
A diet that does not include enough potassium rich foods or
dietary supplements will soon lead to health complications.
Symptoms of a deficiency of potassium in the body include
water retention, heart arrhythmias, continual thirst, high blood
pressure, nerve and muscle dysfunction and vomiting. The
vomiting will lead to a further deficiency in the mineral. These
symptoms, affecting numerous body functions are caused by
the electrolyte imbalance brought on by potassium deficiency.
Dietary sources of potassium
Potassium supplementation: Several potassium supplements
are in the market, including potassium acetate, potassium
bicarbonate, potassium citrate, potassium chloride, and
Potassium is found in a wide range of foods. Potassium rich
foods are easy to find, relatively inexpensive, and are probably
already a part of your regular diet. The best dietary sources of
potassium are fresh unprocessed foods. Many fruits and
vegetables are high in potassium and low in sodium and helps
preventing hypertension (Dickinson et al., 2006; Suter, 1998).
Table 3. Recommend K intake levels
Age
0-6 months:
6-12 months:
1-3 years:
4-8 years:
9-13 years:
14-18 years:
19-30 years:
31-50 years:
51+ years:
Pregnant women:
Lactating women:
Dosage, intake, recommended daily allowance (RDA)
Because deficiency of potassium is rarely observed, there
is no recommended daily allowance for potassium. It is usually
easy to obtain adequate potassium in a normal balanced diet
and this helps to overcome blood pressure and hypertension
(Hermansen, 2000; Myers and Champagne 2007).
In 2004, the Institute of Medicine at the National Academy
of Sciences (Maryland, USA) issued new Adequate Intake (AI)
levels for potassium. The recommendations are as follows:
42
K level
400 mg
700 mg
3.5 g
3.8 g
4.5 g
4.5 g
4.7 g
4.7 g
4.7 g
4.7 g
5.1 g
Potassium and human nutrition: The soil-plant-human continuum..................
potassium gluconate. They are available as tablets, capsules,
effervescent tablets, powders, and liquids. Potassium is also
found in combination with multivitamins. Potassium
supplements, other than the small amount included in a
multivitamin, should be taken only under your doctor’s
supervision, more specifically in case of children.
heart rhythm may occur. People with hyperkalemia or kidney
disease should not take potassium supplements (Chiu et al.,
1997; Whelton et al., 1990). People who take ACE inhibitors
(Ray et al., 1999), potassium-sparing diuretics, or the antibiotic
trimethoprim (Perazella, 2000; Perazella and Mahnensmith, 1997)
and sulfamethoxazole (Bactrim, Septra) should not take
potassium (Alappan et al. 1996; Newnham, 2001).
Precautions
Conclusions
Because of the potential for side effects and interactions
with medications, one should take dietary supplements only
under the supervision of a health care provider (Howes, 1995).
Side effects include diarrhea, stomach irritation, and nausea. At
higher doses, muscle weakness, slowed heart rate, and abnormal
Potassium is an essential element for the health of soil, plant
and humans. Though, the recommended dietary allowances for
humans are not given, it is essential to maintain the normal
potassium levels in the body for various physiological
functions.
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