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23.03.2012.

Calcium(Ca)



Human organism contains calcium more than any other essential mineral, around 1200g per human that weighs 70kg. At least 99% is found in bones and teeth. Calcium is mostly found in bones in the shape of hodroxyapatite( Ca10(PO4)6(OH)2).
Less than one percent of calcium is found in cells and body fluids. It is very significant that calcium concentration in plasma is maintained in tight limits(8,5-10,5 mg/100ml) due to numerous cell functions: muscle contractivity, nervous cells irritability, chormonal influence, blood coagulation, cell moving and other. Calcium is called “second messenger” due to numerous functions that it does connecting to the intracellular protein receptor – calmoduline. Maintenance of this connection leads to numerous enzymes activity modulation, and these are enzymes that enter in cyclic nucleotides metabolism, proteine fosforilation, secretion function, muscular contraction, microtubules assembling, glycogen metabolism and calcium flux.
Calcium level in plasma is maintained through constant releasing from bones in the case that intake of this mineral by food is insufficient.
Calcium is lost from body through urine, feces and sweat(small amount). Amount of this mineral is controlled primarily through degree of absorption in intestines, and urine excretion is constant.
Calcium release from muscle fiber reticulum and vice versa enables contraction. Small variations of calcium in plasma during muscle contraction are made due to mechanical stress. In the conditions of intensive physical work(running especially) comes to releasing of this mineral from bones and lessen building into the bones.
It is shown that stress fractures or sports osteoporosis are more present at some athletes. Specific trainings(long term and exhaustfull)  were connected at these athletes with some hormones depression(estrogen), which are thought to be an important factor for calcium metabolism regulation in bones. Insufficient energy intake at these athletes can also influent to osteoporosis.
Insufficient calcium intake can also exist at athletes that reduce body mass, and along with that high training volume is maintained.

Calcium intake

Milk and dairy products are basic sources of calcium in standard structure of daily meal in Europe and North America. Not only calcium is found in significant concentrations in these groceries, but relationship of calcium and phosphorus is equal(1:1), and absorption is maximal.

Recommended daily amount of calcium and milk, according to age and gender
Groups – age and gender
Optimal daily intake(mg)
Milk portions
Children
1-5
800
3
6-10
800-1200
3-4
Young
11-24
1200-1500
4-5
Women
25-50
1000
3-4
>50, estrogen
1000
3-4
>50, non estrogen
1500
4-5
Ammenorheic female athletes
1200-1500
4-5
Pregnancy or lactation
1200-1500
4-5
Men
25-65 years
1000
3-4
>65 years
1500
4-5




 
In plant groceries( leafy vegetables, cereals, beans, almond) calcium is found in the shape of fitats and oxalats that cannot be degradated in intestines, so absorption from these food is very small.
In a lot of researches is significant sufficient intake of enough calcium intake during childhood and adolescence(till age 25) as a guarantee of maximal bone mass growth and osteoporosis prevention. 

“Athletes’ nutrition”, Marina Djordjevic Nikic

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