CALCIUM METABOLISM AND FEATURES OF ITS ABSORPTION IN THE BODY OF ATHLETES

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ABSTRACT

Calcium is certainly one of the most important elements of the human div. Calcium is necessary for the transmission

of nerve impulses, blood clotting, secretory activity, cell differentiation and death, the implementation of the immune

response, some enzymatic processes, the process of muscle contraction, etc. The concentration of calcium in the

blood can vary by no more than 3% and is subject to strict control by the homeostasis system, and is also regulated by

the hormonal system.

The level of calcium in the blood is regulated by two hormones, as well as calcitriol. In addition, the level of calcium in

the blood can change under the influence of heavy metals. The process of calcium absorption and the processes of its

removal from the div are influenced by many factors - the state of the hormonal system, the quality of food, the

intensity of the training process, etc. At the same time, uncontrolled consumption of calcium by athletes entails

extremely negative consequences.

KEYWORDS

Calcium, calcitriol, parathyroid hormone, calcitonin, homeostasis, hormones, muscles, transport systems.

Research Article

CALCIUM METABOLISM AND FEATURES OF ITS ABSORPTION IN THE
BODY OF ATHLETES

Submission Date:

June 07, 2024,

Accepted Date:

June 12, 2024,

Published Date:

June 17, 2024

Crossref doi:

https://doi.org/10.37547/ijmscr/Volume04Issue06-10

L.T. Seydaliyeva

Department of “Sport Management” at Faculty of “Taekwondo and sports activities” at National University

named after Mirzo Ulugbek, Uzbekistan

S.S. Shukurova

Department of “Sport Management” at Faculty of “Taekwondo and sports activities” at National University

named after Mirzo Ulugbek, Uzbekistan

Journal

Website:

https://theusajournals.
com/index.php/ijmscr

Copyright:

Original

content from this work
may be used under the
terms of the creative
commons

attributes

4.0 licence.

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INTRODUCTION

Calcium is one of the most important elements of the

human div. Calcium is involved in the processes of

transmission of nerve impulses, blood clotting,

secretory activity, cell differentiation and death,

immune response, muscle contraction, etc. The

concentration of calcium in the blood can vary by no

more than 3%, which is the result of control of the

internal environment of the div by the homeostasis

system, as well as the hormonal system. The level of

calcium in the blood is regulated by two hormones:

calcitonin (produced by the thyroid gland, reduces the

concentration of calcium in the blood by reducing bone

resorption, transfers calcium ions from the blood to

bone tissue, reduces the level of tubular reabsorption

in the kidneys, reduces the absorption of ions in the

intestines) and parathyroid hormone (on the contrary,

it increases the level of calcium in the blood, acting

inversely to calcitonin), as well as calcitriol (the active

form of vitamin D in animal organisms, works as a

signaling molecule and regulates the exchange of

calcium and phosphate in the div). Calcium

metabolism in the div can be represented by the

following main sequential stages: absorption of

calcium from the digestive tract and its entry into the

bloodstream;

removal

of

calcium

from

the

bloodstream into tissues and its release back;

excretion in urine and feces. All these processes are

regulated by hormonal factors and biologically active

substances. Classic hormonal regulators of calcium

metabolism include parathyroid hormone, calcitriol

and calcitonin. Parathyroid hormone activates the

process of calcium reabsorption in the distal parts of

the nephron and increases the affinity of ATPase for

calcium [27]. Parathyroid hormone can induce bone

resorption, thereby increasing the differentiation and

activity of osteoclasts. Calcitriol has an alternative type

of action necessary for the process of bone

remodeling,

suppressing

the

growth

and

differentiation of osteoblasts, the synthesis of

collagen,

osteopontin,

casein

kinase,

and

mineralization of the bone matrix. Calcitriol activates

monocytes, stimulates their transformation into

macrophages and osteoclasts, and the number of

vitamin D receptors in these cells decreases as they

differentiate and transform into osteoclasts [5,6].

Calcitonin inhibits the processes of resorption of both

calcium and the protein matrix. This is manifested by a

decrease in hydroxyproline excretion and calcium

levels in the blood [5-7]. Calcitonin also inhibits the

activity of osteoclasts and reduces their number.

Already 1 hour after calcitonin administration, the

formation of osteoclasts from progenitor cells

decreases [61]. Other hormones can also affect calcium

levels in the div. For example, prostaglandins mimic

the effect of parathyroid hormone and cause bone

resorption. Low doses of glucocorticoids promote

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bone growth. They inhibit the development of bone

tissue only when their excess production persists for a

long time [5,6,17,20,21]. Currently, the family of

calcium-regulating hormones has been expanded. A

new member is klotho, due to its ability to regulate

intracellular Ca transport through modulation of cation

channels [24]. The regulation of calcium metabolism in

the intestines and kidneys is carried out by almost the

same hormones and biologically active substances. For

example, modulation of paracellular permeability is

carried out by bacterial toxins, growth factors,

cytokines, etc. It has been shown that parathyroid

hormone stimulates passive calcium transport,

increasing the electromotive force and thereby

increasing the efficiency of intercellular transport [28].

Blood calcium levels can be affected not only by

hormonal influences, but also by many heavy metals. It

is known that divalent metals are capable of so-called

“mimicry”

- imitating the action of calcium, and even

displacing calcium in some physiological processes,

and using its specific transport systems to penetrate

the cell [20,21,22]. Lead, cadmium, molybdenum, etc.

compete with calcium for common binding sites with

intestinal glycoproteins, which are necessary in the

absorption process. With a massive intake of heavy

metals into the div, which is observed during chronic

intoxication, they use the transcellular pathway of

calcium transport, load its transport systems and limit

the consumption of the element, so hypocalcemia may

develop. However, they displace calcium from bone

tissue, so the level of calcium in the blood remains

unchanged or in some cases may even increase. We

have shown that under conditions of intoxication with

lead, cadmium, zinc and other xenobiotics, there is a

significant accumulation of heavy metals in the femurs

of

rats,

associated

with

their

pronounced

demineralization [25,26,27]. Thus, we can conclude

that no matter how diverse and important the

functions of calcium are in the div, the system of

maintaining its homestasis is so complexly organized.

The need for such strict control is dictated by a rather

narrow range of fluctuations in the concentration of

calcium in the blood, which would not cause significant

changes in the human div.

Total blood calcium, which is normally 2.1-2.6 mmol/l, is

the sum of calcium associated with bicarbonates,

lactate, citrates, phosphates, the proportion of calcium

in such compounds is 7%, associated with blood plasma

proteins (mainly albumin ) the proportion of calcium is

46% and the ionized fraction of calcium is about 47% [1,

2]. However, the bulk of calcium is concentrated in

bone tissue, which serves as a kind of buffer for calcium

ions circulating in the bloodstream. Calcium is also

exchanged between the bone matrix and extracellular

fluid - more than 500 mmol of the mineral. There is a

rapidly exchanging calcium pool of approximately 500

mmol and a slowly exchanging pool of 7-7.5 mmol [3].

The total content of the element in tissue cells can

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reach 10 mmol/kg. Most of it is represented by soluble

ligands and cell membranes and is concentrated in

intracellular depots. The volume of intracellular

calcium consists of: calcium localized inside cellular

organelles; chelated calcium (associated with an anion

or cytoplasmic protein molecule); ionized calcium

(free) [4]. Calcium metabolism in the div consists of

three stages: 1) absorption from the digestive tract and

its entry into the bloodstream; 2) entry from the

bloodstream into the tissues of the div (and vice

versa); 3) excretion in urine and feces [5]. A mature

person needs 20-37.5 mmol (0.8-1.5 g) of calcium daily;

in pregnant and lactating women this need is twice as

high [1, 6]. The calcium requirement for athletes is

higher on average by 20-25%.

Calcium metabolism is regulated by three main

transport systems: intestinal absorption, renal

reabsorption and metabolism in bone tissue. In the

gastrointestinal tract, during the process of digestion

and absorption, only half of the total calcium received

is absorbed [5,7,8]. Its transport through intestinal

enterocytes into the blood occurs more intensively

than the transport of iron, manganese and zinc, but 50

times slower than sodium. It is believed that calcium

absorption in humans and other mammals occurs

mainly in the small intestine, primarily in the

duodenum, where the intensity of this process per unit

length is highest, although more calcium is absorbed in

the jejunum and ileum due to their considerable extent

. In addition, calcium absorption also occurs in the large

intestine [7,8,9,10,19]. Therefore, the state of the

digestive tract is important in the process of

absorption of consumed calcium. Absorbed calcium

enters the general bloodstream and is distributed to

various tissues of the div. The bulk of calcium enters

bone tissue, where it accumulates, increasing bone

mineralization. Here calcium works together with

phosphorus. Calcium and phosphorus are the main

components of bone tissue, forming, firstly,

hydroxyapatite crystals, which are deposited in the

bone matrix and provide skeletal strength, and

secondly, more soluble amorphous calcium phosphate,

which is a labile reserve of calcium and phosphorus

ions. In addition, these elements can regulate the

cellular composition of bone - the ratio of osteoclasts

and osteoblasts [17,18,23].

To achieve higher peak bone mass, in some sports,

vitamin D (600 IU/day) is prescribed in combination

with sufficient calcium (1200 mg/day), especially at a

young age[9,13,15]. However, a number of studies have

found that excess calcium in brain cells can lead to the

formation of toxic clusters that are a hallmark of

Parkinson's disease. An international team led by the

University of Cambridge has found that calcium may

mediate interactions between small membrane

structures inside nerve endings that are important for

neuronal signaling in the brain and alpha-synuclein, a

protein associated with Parkinson's disease. Excess

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levels of calcium or alpha-synuclein can cause a chain

reaction that leads to the death of brain cells. Also,

some investigators have found that patients with

calcium detection also had higher rates of obstructive

coronary artery disease, revascularization, and/or

other major adverse cardiac events in subsequent

years[14,16,20].

Several studies have suggested that taking calcium

supplements may help with weight loss. This

hypothesis has gained some currency and was based

on the idea that high calcium intake may reduce

calcium concentrations in fat cells, reducing the

production of parathyroid hormone and the active

form of vitamin D. Reducing intracellular calcium

concentrations, in turn, may increase fat breakdown

and inhibit fat accumulation in these cells. Also, calcium

from food or supplements, according to some

hypotheses, may bind small amounts of dietary fat in

the digestive tract and interfere with the absorption of

this fat [17,23,24,25,26,27]. Dairy products, for

example, may contain additional components that

have an even greater effect on div weight, regardless

of their calcium concentration. Protein and other

components of dairy products can modulate hormones

that regulate appetite and thus indirectly influence

weight. A 2014 study of 15 healthy young men found

that diets high in milk or cheese (providing a total of

1,700 mg/day calcium) significantly increased fecal fat

excretion compared to a control diet that provided 500

mg calcium/day. day. However, results from clinical

trials that examined the effects of calcium on div

weight were largely negative. For example, a 1500

mg/day supplement was studied among 340

overweight or obese adults with mean baseline

calcium intakes of 878 mg/day (treatment group) and

887 mg/day (placebo group). Compared with placebo,

calcium supplementation for 2 years had no clinically

significant effect on weight.

The removal of calcium from the div is ensured

mainly by its secretion from the blood into the

intestinal lumen and subsequent removal with

excrement, which accounts for 70-80%. However, the

kidneys also play an important role in calcium

excretion. In humans, about 240 mmol of calcium per

day is filtered in the kidneys, 97-99% of the filtered

calcium (about 234 mmol) is reabsorbed by tubular

epithelial cells, and only 6 mmol is excreted in the urine

[9,10,11,12,24].

Calcium absorption depends on vitamin D intake and

status [17]. The efficiency of absorption is related to

the physiological requirements for calcium and

depends on the dosage. Dietary calcium absorption

inhibitors include substances that form complexes in

the intestine. Protein and sodium may also alter

calcium bioavailability, as high calcium levels increase

urinary excretion. Although the amount absorbed in

the intestine is increased, the net result may be a

decrease in the proportion of calcium directly used by

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the div [22,28,29]. The absorption, as well as the

processes of calcium excretion in the div, depend to

some extent on other food components. For example:

Caffeine may increase urinary calcium loss and

decrease calcium absorption. However, the effects of

caffeine remain relatively modest, and this effect was

primarily noted in women with insufficient calcium

intake during menopause.

Lactose

–

promotes calcium absorption.

Magnesium

–

Moderate to severe magnesium

deficiency can lead to hypocalcemia. However,

according to some studies in which magnesium was

artificially removed from the diet, it was found that

even a small decrease in the amount of magnesium

consumed can lead to quite a serious decrease in

serum calcium concentrations.

Oxalic acid can also interfere with calcium absorption.

Foods rich in oxalic acid include spinach, sweet

potatoes, rhubarb and beans.

Phytic acid. May interfere with calcium absorption.

Found in unleavened bread, raw beans, nuts, grains

and soy products.

Protein - there is an opinion that dietary protein can

lead to increased excretion of calcium in the urine, but

this issue is still being studied by scientists and there is

no clear answer yet.

Sodium. Moderate and increased consumption of

sodium chloride (salt) leads to an increase in the

amount of calcium excreted from the div in the urine.

However, there are no published recommended

calcium intakes based on salt intake.

Zinc. Since calcium and zinc are absorbed in the same

part of the intestine, they can mutually influence the

metabolic process. Large doses of zinc consumed may

interfere with absorption.

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