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Calcium (Ca ++) is an extremely important mineral salt for the human body, which is still the subject of numerous studies.

Calcium is the most abundant mineral element in the human body. By binding to phosphorus (P), it first of all plays a very important structural function (ratio 2.5: 1). The two salts, in fact, unite and crystallize forming hydroxyapatite . This "complex" mineral salt, depositing itself neatly thanks to the orientation of some specific connective proteins (extracellular matrix), gives shape and structure to the bones, therefore to the skeleton.

In hydroxyapatite, about 98-99% of the total calcium is found; in this way, the bones of the skeleton, in addition to being a real "scaffolding" for the muscles, and a shield for the organs, act as a reservoir of minerals. It is therefore possible to deduce that calcium can be mobilized by the bone "reservoir" to comply with some vital plasma and extracellular requirements (metabolic priority). The physiological mechanisms that require calcium ion are numerous: enzymatic activations, nerve impulse transmission, muscle contraction, membrane permeability, cell multiplication and differentiation (in total, about 1-2% of total body calcium); the hormones responsible for calcium metabolism are: parathormone, calcitriol (active form of vitamin D) and calcitonin .

Absorption

To learn more: Calcium absorption »

On average, only 35-40% of dietary calcium is absorbed by the body. This capacity varies considerably based on the dietary intake of mineral salt, in part due to the state of nutrition (intake of vitamin D), in part to hormonal flows (see above: hormones responsible for calcium metabolism) and on the basis of age of the subject. The human intestine has the greatest potential for absorption in childhood and, gradually, this is reduced with aging, during which there is a significant reduction of 1, 25 (OH) 2 cholecalciferol .

The calcium introduced with the diet is absorbed by two distinct ways: the first is saturable and occurs with an active transcellular transport mechanism; this process is mediated by a vit peptide. D-dependent ( Calcium Binding Protein ) located in the outer membrane of enterocytes (cells of the intestinal mucosa) that binds calcium and transfers it to the basement membrane where it is introduced into the bloodstream by calcium-magnesium ATPase . The second route of absorption is passive diffusion, a process that is independent of the intervention of any hormonal factor.

Overall, calcium absorption is an extremely variable capacity, as it remains influenced by:

Subject's soccer requirement
Presence of other molecules in the meal that influence the bioavailability of calcium:

Increased by the presence of vit. D
Increased by the presence of sugars, especially lactose
Increased by the presence of lysine and arginine amino acids
Increased by the presence of a basic intraluminal pH
Decreased by the presence of oxalates (anti-nutritional molecules)
Decreased by the presence of phytates (anti-nutritional molecules)
Decreased by the presence of phosphates
Decreased by the presence of nervines (caffeine, alcohol - anti-nutritional molecules)
Decreased by the presence of uronic acids (of dietary fiber - anti-nutritional molecules)
Decreased concurrently with pathological malabsorption.

Excretion

The calcium present in the body (excluding that of the unabsorbed and intraluminal meal) is partially expelled by means of: feces, urine and sweat.

In the faeces it is poured with intestinal secretions (100-200mg / day); in urine, on the other hand, the excretion of calcium varies considerably based on subjectivity and the state of nutrition.
They are elements predisposing to the urinary excretion of calcium: sodium, phosphorus and proteins (even if the latter, on the basis of recent investigations, do not seem to be directly related to the phenomenon but contribute to the overall acid-base balance - see PRAL); it is therefore deducible that the nutritional excess of these three elements can increase the urinary elimination of calcium.
Soccer sweat losses can also be significant (see sportsmen).

Calcium metabolism involves the iteration of numerous physiological systems responsible for increasing / maintaining the skeletal structure and general homeostasis (plasma, extracellular and intracellular fluids).

Serum calcium (or calcemia) is regulated mainly by:

Intestinal absorption
Activation of vit. D by the liver and kidneys (mixed function: intestinal pro-absorbent, increases bone resorption and increases the specific capacity of parathyroid hormone)
Resorption or excretion of calcium by the kidneys depending on:

synthesis and secretion of calcitonin by the parafollicular thyroid cells (serum IPOcalcimizing)
synthesis and secretion of the parathyroid hormone by parathyroid (serum IPcalcimizing).

Intra and extracellular calcium varies its concentrations based on serum calcium, concentration gradient and specific cyto-histological equilibrium mechanisms.

On the bone level, however, calcium is regulated mainly by the activity of specific cells such as: osteoblasts, osteoclasts and osteocytes. For more information, read the article on bone metabolism.

Calcium in food and water

Calcium is a nutritional component present both in food and in water, however, there are many doubts about the real bioavailability of mineral salt deriving from some dietary sources.

The foods that make the most dietary calcium are those belonging to the milk and derivatives group (65% of the total content of a "typical" diet). Vegetables and vegetables follow (12%), cereals (8.5%) and finally meat and fish (6.5%); the eggs do not contain large quantities of calcium, while the legumes, although making (in some cases) noteworthy levels, due to the high content of anti-nutritional molecules (see previous paragraph), may not constitute a significant source. It is however necessary to specify that in the case of legumes, but also of cereals, vegetables and fruit (dry and fresh), some molecules responsible for the reduction of bioavailability can be moderate / inhibited for: extraction - dilution (soaking, replacement and cooking in water), physical-chemical treatments, interactions with other intrinsic or extrinsic factors of food and fermentation of intestinal bacterial flora. In particular, this last component could significantly increase the absorption of NOT bioavailable calcium in the colon-cecum intestine.

The waters rich in mineral salts, or those with a very high fixed residue, make use of excellent concentrations of calcium (400mg / l) and other salts; on the other hand, some currents of thought suggest that the calcium contained in water is NOT really absorbable and therefore should NOT be counted in the overall dietary intake of the mineral salt in question. To tell the truth, the experimental studies have given contrasting results and, in order to guarantee the recommended intake levels, it would be desirable to cover the dietary calcium requirement exclusively by means of food.

requirement

The nutritional requirement of calcium is greater in skeletal development, pregnancy, lactation and also in the osteoporotic prevention phase (seniority) than in adulthood. It does NOT follow a unidirectional progression / digression even if, for a more accurate estimate of the structural and metabolic needs, in addition to the absolute quantity of calcium (mg per day), it would be rather necessary to evaluate the ratio between the absolute daily calcium requirement and the total (or skeletal) mass of the subject (mg per day of calcium / kg of the subject). For example:

a 9-month-old infant weighing 8.5kg has a daily calcium requirement of 600mg / day, a 45-year-old adult on a normal weight with a mass of 60.5kg has a daily calcium requirement of 800mg / day, while an elderly female in menopause of 56kg is characterized by a daily calcium requirement of 1500mg / day.

For an elusively quantitative or absolute evaluation, the elderly female in menopause seems to have a calcium requirement higher than that of the adult and the infant but, if we calculate the ratio between the daily requirement of calcium and the total mass of the organism (improperly defined "weight"), we obtain a proportion to the benefit of the infant on the other two:

Suckling:	600mg / 8.5kg = 70.6
Elderly female in menopause:	1500mg / 56.0kg = 26.8
Adult:	800mg / 60.5kg = 13.2

It is therefore an established fact that the proportional (or relative) need for calcium is higher in infants, despite the absolute one (based on what was quoted by the LARN - Recommended Energy and Nutrient Intake Levels for the Italian population) to favor the elderly females in menopause without estrogen replacement therapy.

NB . We recall that the high calcium requirement of subjects in old age is also related to the reduced absorption capacity described in the previous paragraphs, as well as to the risk of skeletal compromises which we will discuss later.

Recommended daily calcium rations

The Italian population takes on average about 820mg / day of calcium from the diet, however, based on gender and age, calcium needs change significantly. Infants need 600mg / day of calcium, while children from 1 to 6 years 800mg / day; from 7 to 10 you need 1000mg / day of calcium and 11 to 17 about 1200mg / day. From 18 to 29 years the population needs 1000mg / day and from 30 to 49 again 800mg / day. Over the age of 60, males may be limited to 1000mg / day, while menopausal females should reach 1200-1500mg / day (based on the presence or absence of estrogen replacement therapy). Pregnant women and nurses need 1200mg / day of calcium.

Excess

The excesses of alimentary calcium are rare and the respective adverse metabolic consequences are mainly due to the incorrect pharmacological administration of vit. D or by intravenous injection of calcium; in parallel, an excessive intake of the mineral could inhibit the absorption of other salts such as iron and zinc. Some studies have also described a possible hypotensive effect due to high levels of food calcium.

shortage

To learn more: Calcium deficiency »

Sub-optimal rations of food calcium can cause considerable damage to the body; during growth, calcium deficiency can lead to failure to achieve peak bone density or even reduced chronic skeletal density as a major predisposing factor for sexually indiscriminate geriatric osteoporosis. In addition to the addition of calcium, the vit. Share is also decisive for reaching / maintaining the peak bone mass. D food and endogenous, and physical motor activity (especially in development and in the third age).

In old age, osteoporosis mainly affects the female sex who must endure the sudden interruption of estrogenic activity (primary etiological factor for female osteoporosis). It is no coincidence that the achievement of higher levels of calcium in the elderly CARENTI subjects is effective in reducing the pathological PROGRESS but NOT in the treatment. Ultimately, the calcium levels in the diet of the elderly have a decisive role in the pathological course but do not seem to be related to the primary onset of the disease, instead more influenced by the factors described above: peak bone mass and interruption of estrogenic activity.

The infant's deficient form of calcium is mainly linked to a deficiency of vit. D and / or intake of foods with a low calcium to phosphorus ratio (Ca / P). With regard to the salt balance between calcium and phosphorus in the diet, read the article: The right balance between calcium and phosphorus.

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