Calcium Importance and Absorption

Calcium stands as one of the 21 vital elements essential for human well-being, and its health benefits do not materialize in isolation; rather, its effectiveness hinges on maintaining adequate levels of vitamin D.

Two categories of calcium are discernible: one tightly bound within bones and another more easily accessible type located on the bone surface.

The skeletal framework serves as a reservoir of minerals for the body, with 99% of the body's calcium stored in bones and teeth, providing structural support. The remaining 1% is dispersed in intracellular and extracellular fluids, allowing the body to draw from skeletal reserves during periods of low blood calcium levels and replenish them as necessary.

A continuous supply of calcium is vital throughout life, particularly during growth phases, pregnancy, and lactation (breastfeeding).

Calcium plays a pivotal role in the secretion of hormones and enzymes, facilitates the efficient functioning of neurotransmitters, and is indispensable for muscle and blood vessel contraction.

In the bloodstream, calcium concentration typically ranges from 2.25 to 2.5 mmol. Approximately 40-45% of this quantity binds to plasma proteins, 8-10% forms complexes with ions like citrate, and 45-50% exists as dissociated free ions.

Around 10-40% of dietary calcium is absorbed in the small intestine with the aid of vitamin D, and the body augments calcium absorption in the event of deficiency.
Calcium Importance and Absorption

Digestion and absorption of nutrients

The primary functions of gastrointestinal system are ingestion, digestion, absorption of nutrients and excretion of solid waste.

The body requires the consumption of nutrients to support physiological activity.

Proper function of the gastrointestinal system (GI) is essential for normal growth and for maintaining fluid and electrolytes balance.

For the assimilation of nutrients by the body, the bulk of the foodstuffs must first undergo mastication and digestion.

In this process, polymeric substances such as starches, proteins and triglycerides are broken down into their smaller segments “building blocks” of monomeric sugars, amino acids, fatty acids, etc., in preparation for absorption.

With the exception of most vitamins and inorganic substituent, this digestive breakdown process is necessary for absorption into the body.

It is also a factor in body defenses, preventing the potential absorption of “foreign” macromolecules. The GI tract is the largest immune system organ whose primary functions include the digestion and absorption of ingested nutrient and the protection of the body from ingested microorganism and noxious substances.

During digestion/hydrolysis if the polymeric nutrients (especially) the proteins), the vitamins and trace elements associated with them are released, allowing their more efficient absorption.

The large intestine absorbs water and electrolytes from entering content, which happens predominantly in the proximal half and stores fecal matter until defecation, which occurs in the distal half.

Absorption is the process by which the end products of digestion such as monosaccharides, amino acids, glycerol, fatty acid chains, vitamins, minerals and water – pass through the epithelial membranes in the small and large intestine into the blood or lymph system.

The mechanisms for digesting and absorbing major nutrients are fully mature in the premature and term infant.
Digestion and absorption of nutrients

Digestion and absorption of fat during infant stage

Newborn are limited in their ability to digest and absorb certain nutrients due to decreased activity of specific enzymes and other substances as well as functional and anatomic limitations.

The complex process of digestion/absorption can be optimally effective only when the GI tract and accessory organs are totally develop and fully functioning.

The gastrointestinal (GI) system is a complex organ system that extends from the mouth to the anus and includes the esophagus, stomach, small and large intestines, liver, and pancreas.

Not only must the muscular tube (alimentary canal) with it a mucosal lining and endocrine cells be operating efficiently in conjunction with the nervous system, but the accessory organs (pancreas, liver, and gallbladder) with their important digestive secretions also must be physiologically mature.

The secretion of gastric, intestinal and pancreatic digestive enzymes is not developed to adult levels in young infants.

Nevertheless, the infant is able to digest and absorb the nutrients in human milk fully and efficiently and breast milk contains enzymes that contribute to the hydrolysis of fat, carbohydrate and protein in the gut. 

Good examples of the emphasis on GI tract maturity are the care given to the fat in infant formula and the time and sequence of the introduction of various foods into the infant’s diet.

The infant pancreas, although structurally mature at term, is usable for several months to produce enzymes sufficient for effective digestion.

Pancreatic lipase, alpha-amylase and the proteolytic enzymes are in too short supply to accommodate digestion of a mixed diet. Digestion of fat is a real concern due to decreased levels of bile salts from the liver as well as low lipase release from the pancreas.

Bile salt low because of decreased syntheses and decreased intestinal reabsorption. While fetal lipase levels are detected at 21 weeks gestation, but do not reach adult concentrations until 6 months of age in the term infant.
Digestion and absorption of fat during infant stage

Absorption of calcium

In human, near 30% of the daily dietary calcium intake, about 1 gram, is absorbed in the intestinal tract. And average daily losses of calcium are estimated to be 320 milligrams.

Calcium absorption in intestine and its re-absorption in kidney involve similar processes that include both passive paracellular and active transcellular pathways.

Absorption of calcium involves an epithelial calcium channel, specifically transient receptor potential channel and the calcium-binding transport protein calbindin 9K, which binds calcium for transport into cell.

The complexity of the calcium absorbing system arises because the level of dietary calcium, and consequently of luminal calcium, can vary over very wide limits and also the level of a activity of the different mechanisms for calcium varies on passing from duodenum to jejunum and ileum.

Factors that improve calcium absorption include adequate amounts of protein, magnesium, phosphorous, and vitamin D.

Calcium is best absorbed in an acid environment. Therefore calcium is better absorbed when no consumed with antacids.

The absorption of calcium also depends on the presence of adequate amounts of vitamin D, which works with parathyroid hormones to regulate the amount of calcium in the blood.

Conditions that reduce calcium absorption include high or excessive intakes of oxalates and phytates, found in foods such as spinach and unleavened whole wheat products.

Stress also can reduce absorption of calcium.

Lack of exercise can reduce calcium absorption as well as cause an increase in calcium losses. These life habits can immobility lead to calcium deficiency. Calcium deficiency can increase risk of bone disorders such as osteoporosis.

Calcium is absorbed along the small intestine, more in the duodenum and proximal jejunum than the ileum. The absorption of calcium is completed within 4 hours after its oral intake.

Absorption of calcium