What makes the body’s absorption of minerals vary

It means the minerals in soil and water easily find their way into your body through the plants, fish, animals, and fluids you consume.

Many micronutrients interact. Vitamin D enables your body to pluck calcium from food sources passing through your digestive tract rather than harvesting it from your bones. Vitamin C helps you absorb iron. And even a minor overload of the mineral manganese can worsen iron deficiency. Water-soluble vitamins are packed into the watery portions of the foods you eat.

They are absorbed directly into the bloodstream as food is broken down during digestion or as a supplement dissolves. Because much of your body consists of water, many of the water-soluble vitamins circulate easily in your body. Your kidneys continuously regulate levels of water-soluble vitamins, shunting excesses out of the body in your urine. Although water-soluble vitamins have many tasks in the body, one of the most important is helping to free the energy found in the food you eat.

Others help keep tissues healthy. Here are some examples of how different vitamins help you maintain health:. Contrary to popular belief, some water-soluble vitamins can stay in the body for long periods of time. And even folic acid and vitamin C stores can last more than a couple of days. Just be aware that there is a small risk that consuming large amounts of some of these micronutrients through supplements may be quite harmful.

For example, very high doses of B6—many times the recommended amount of 1. Rather than slipping easily into the bloodstream like most water-soluble vitamins, fat-soluble vitamins gain entry to the blood via lymph channels in the intestinal wall see illustration. Many fat-soluble vitamins travel through the body only under escort by proteins that act as carriers. Fatty foods and oils are reservoirs for the four fat-soluble vitamins.

Within your body, fat tissues and the liver act as the main holding pens for these vitamins and release them as needed. To some extent, you can think of these vitamins as time-release micronutrients. Your body squirrels away the excess and doles it out gradually to meet your needs. Together this vitamin quartet helps keep your eyes, skin, lungs, gastrointestinal tract, and nervous system in good repair.

Here are some of the other essential roles these vitamins play:. Because fat-soluble vitamins are stored in your body for long periods, toxic levels can build up. This is most likely to happen if you take supplements. The body needs, and stores, fairly large amounts of the major minerals. Major minerals travel through the body in various ways. Potassium, for example, is quickly absorbed into the bloodstream, where it circulates freely and is excreted by the kidneys, much like a water-soluble vitamin.

Calcium is more like a fat-soluble vitamin because it requires a carrier for absorption and transport. One of the key tasks of major minerals is to maintain the proper balance of water in the body. Sodium, chloride, and potassium take the lead in doing this.

Three other major minerals—calcium, phosphorus, and magnesium—are important for healthy bones. Sulfur helps stabilize protein structures, including some of those that make up hair, skin, and nails. Having too much of one major mineral can result in a deficiency of another. These sorts of imbalances are usually caused by overloads from supplements, not food sources.

Here are two examples:. A thimble could easily contain the distillation of all the trace minerals normally found in your body. Yet their contributions are just as essential as those of major minerals such as calcium and phosphorus, which each account for more than a pound of your body weight. The other trace minerals perform equally vital jobs, such as helping to block damage to body cells and forming parts of key enzymes or enhancing their activity. Trace minerals interact with one another, sometimes in ways that can trigger imbalances.

Too much of one can cause or contribute to a deficiency of another. However, when iron concentrations are reduced, the protein loses aconitase activity and functions as an iron binding protein IRP. IRPs interact with iron response elements IREs of the mRNA to regulate the synthesis of proteins involved with iron transport, storage, and use, in response to changes in cellular iron concentrations [30] Figure 1.

The new born infant has a total of about mg in the body. The total body iron in an adult male is to mg. In contrast, the average adult woman has only mg of iron in her body. This difference may be attributed to lesser iron reserves in women, lower concentration of hemoglobin and a smaller vascular volume than men. Control of iron uptake is undoubtedly of principal importance due to the lack of a regulated means of excreting iron.

Once the food is consumed and digested, dietary iron is mainly absorbed in the duodenum and proximal jejunum. Reasonably, haem iron is absorbed more efficiently than non-haem iron, apparently by endocytosis of the intact iron—protoporphyrin complex at the enterocyte brush border. After the digestion iron from all dietary sources enters a common intracellular pool from which depending on the iron status of individuals it is either stored as ferritin in the enterocyte or exported from the enterocyte via the ferroportin transporter on the basal side of the cell.

Infants, children, teenagers, and women of childbearing age are commonly affected by iron deficiency; whereas healthy adult males are seldom deficient. The earliest stage of iron deficiency is characterized by loss of storage iron indicated by ferritin and is called iron depletion or prelatent iron deficiency.

The concentrations of serum iron and the iron-carrying serum protein transferrin are normal at this stage. When iron stores are exhausted serum ferritin Symptoms frequently associated with iron deficiency anemia include palor, weakness, fatigue, dyspnea, palpitations, sensitivity to cold, abnormalities in the oral cavity and gastrointestinal tract, and reduced capacity for work [33].

Iron overload is associated with increases in non-protein bound iron resulting from the physiologic iron-binding capacity being overwhelmed [37].

Disadvantages with overload are for example increased risk for bacterial infection and cardiomyopathy. Overload can result from inborn errors in metabolism leading to hyper-absorption of iron or inadequate synthesis of the iron-binding proteins.

Overload can also result from excessive absorption of dietary iron due to various causes including chronic ingestion of greater than adequate amounts of dietary iron, especially heme iron. These observations concerning of iron overload have raised the question as to whether or not general fortification of food with inorganic iron is beneficial [37]. Dietary factors contribute a significant role in the development of iron deficiency and then iron deficiency anemia. Iron absorption by the gut enterocytes controls iron balance but there is no route of controlled iron excretion.

This means that iron absorption is regulated by dietary and systemic factors. Ferrous iron is transported across the apical membrane of the duodenum by the divalent metal transporter 1 DMT1 , which is localized on the brush border membrane close to dcytB. Ascorbic acid is one of the most effective enhancer of non-heme iron absorption. Other dietary factors such as citric acid and other organic acids, alcohol and carotenes similarly enhance non-heme iron absorption [38].

Meat also promotes non-heme iron absorption by activating gastric acid production. Conversely, absorption of non-heme iron is inhibited by phytic acid inositol hexaphosphate and inositol pentaphosphate in grains and cereals and by polyphenols in some vegetables, coffee, tea, and wine.

These inhibitors bonded to non-heme iron so it is not available for uptake. Dietary factors influencing iron absorption are outlined in Table 1. Calcium: Calcium does inhibit both non-heme iron and heme iron absorption. Calcium inhibits the absorption of both heme and nonheme iron in a comparable way and thus, it is likely that this inhibition by calcium occurs after the heme iron is freed from the porphyrin ring [40]. Further increasing the amount of dairy products above a basal level of mg appears to have no further inhibiting effect on iron absorption Galan et al.

However, the duration of the inhibitory effect of calcium on iron absorption has been shown to be less than two hours [46]. On the other hand, ingestion of mg Ca as the carbonate daily with meals over a twelve-week period did not appear to be harmful to their iron status [47].

Phytate: During digestion, the phytate molecule can be negatively charged, indicating a potential for binding positively charged metal ions like iron [48]. The negative consequence of phytate in bran on iron absorption was first demonstrated by Sharpe et al. This effect was earlier supposed to be because of its high content of phytate which has been demonstrated in a number of more recent studies [23,50]. Brune et al.

They examined vegetarians and non-vegetarians and found that no adaptation of intestinal brush border to a high phytate intake and concluded that the satisfactory iron stores in the vegetarian group were due to a high consumption of organic acids like ascorbic acid. Several methods of preparations of cereal grains including soaking, germination and fermentation have been shown to completely reduce the phytate content of cereals and vegetables under optimal conditions [52] and could thereby eliminate their effects on iron absorption.

In addition, negative effects of phytate and fiber on iron absorption have been demonstrated in the rat [53], found a reduction in iron absorption when high fiber breads were fed to rats.

However, the magnitude of this inhibition was unrelated to the amount of phytate phosphorus or dietary fiber present in the diet. In contrary, results from experiments by [54], indicated higher absorption from FeSO4 than from the endogenous Fe present in bread, both expressed as mg Fe absorbed and fractional Fe absorption.

Using balance and single meal radioisotope measures, she found no differences in Fe absorption among three different breads with fiber contents of This indicates indirectly that the inhibitory effect of fiber on iron absorption is probably due to the phytate in the fiber fraction and further supports the study of Morris and Ellis [56], who found that iron absorption in rats was higher from dephytinized bran.

Phenolic Compounds: During digestion, the phenolic compounds from the food or beverage released and can form complex with Fe in the intestinal lumen making it unavailable for absorption.

Similarly, the consumption of black tea and coffee has been shown to strongly inhibit iron absorption from composite meals [16,25,26], with coffee having about half the inhibitory effect of tea. Moreover, Prashanth et al. Gaur and Miller [61], reported that the percentage values for total dialyzable iron, total soluble iron and soluble iron.

This was reported by several authors. There are two mechanisms for this effect of nonheme iron on absorption. Adding high amounts of ascorbic acid to daily diets for a longer period have in several studies failed to increase ferritin levels [] although single meal absorption measures using radio iron have in the same subjects indicated that ascorbic acid enhances the iron absorption.

When a glass of orange juice is included in a breakfast meat, iron absorption can be increased 2. Meat: The absorption of iron particularly of heme iron is influenced very little by other food components in the diet with the exception of meat which enhances absorption and calcium which inhibits iron absorption [40]. Meat also increases the absorption of nonheme iron [67,68]. The mechanism behind this enhancing effect of meat on both heme and nonheme iron absorption is as yet unknown.

It has however been reported by Hurrell et al. Initially, meat may enhance nonheme iron absorption by stimulating production of gastric acid, and thereby promoting iron solubilization within the stomach.

Thereafter, a meat factor s may chelate the solubilized iron in the acidic lower pH environment of the stomach and thereby maintain iron solubility during intestinal digestion and absorption. Fish and poultry also have an enhancing effect on nonheme iron absorption [70]. Alcohol: Alcohol increases the absorption of nonheme iron slightly in man [16]. It has been shown that chronic alcohol abusers have increased serum ferritin concentrations and calculated total body iron compared with nondrinkers although it is controversial whether the alcohol affects the actual absorption process of iron.

Both the source and chemical form of dietary iron can markedly affect its availability for absorption. In the vegetable category, the staples rice, maize, wheat, and beans have either moderate or poor iron availability [71]. Other sources of nonheme iron are compounds added to fortify the diet with additional iron above its endogenous level. The most common sources are soluble iron salts or small-particle elemental iron. When taken without food, ferrous salts are better absorbed than ferric forms [].

This is probably related to the fact that ferric iron is insoluble in aqueous solution above pH 3, whereas the majority of ferrous iron remains soluble at pH 8. In terms of the change in entropy D S of the dissolution process, most dissolution processes lead to a greater randomness and therefore an increase in entropy. In fact, for a large number of dissolution reactions, the entropic effect the change in randomness is more important than the enthalpic effect the change in energy in determining the spontaneity of the process.

The figure on the left schematically shows the enthalpy changes accompanying the three processes that must occur in order for a solution to form: 1 separation of solute molecules, 2 separation of solvent molecules, and 3 interaction of solute and solvent molecules.

The overall enthalpy change, D H soln , is the sum of the enthalpy changes for each step. In the example shown, D H soln is slightly positive, although it can be positive or negative in other cases. The figure on the right schematically shows the large, positive entropy change, D S soln , that occurs when a solution is formed.

Although D S soln is generally positive, this value could be negative in certain situations involving the dissolution of strong ions. In general, if the solute and solvent interactions are of similar strength i. Therefore, the increase in entropy determines spontaneity in the process.

However, if the solute and solvent interactions are of differing strength i. Hence, the increase in entropy that can occur is not enough to overcome the large increase in enthalpy; thus, the dissolution process is nonspontaneous.

To illustrate the importance of D H and D S in determining the spontaneity of dissolution, let us consider three possible cases: The dissolution of a polar solute in a polar solvent. The polar solute molecules are held together by strong dipole-dipole interactions and hydrogen bonds between the polar groups.

The nonpolar solute molecules are held together only by weak van der Waals interactions. Hence, the enthalpy change to break these interactions step 1 is small. The nonpolar solute molecules do not form strong interactions with the polar solvent molecules; therefore, the negative enthalpy change for step 3 is small and cannot compensate for the large, positive enthalpy change of step 2.

Therefore, the dissolution does not occur spontaneously. The nonpolar solvent molecules are also held together only by weak van der Waals interactions, so the enthalpy change for step 2 is also small.

Even though the solute and solvent particles will also not form strong interactions with each other only van der Waals interactions, so D H 3 is also small , there is very little energy required for steps 1 and 2 that must be overcome in step 3. The principles outlined in the green box above explain why the interactions between molecules favor solutions of polar vitamins in water and nonpolar vitamins in lipids.

The polar vitamins, as well as the polar water molecules, have strong intermolecular forces that must be overcome in order for a solution to be formed, requiring energy. When these polar molecules interact with each other i. Hence, the overall enthalpy change energetics is small.

The small enthalpy change, coupled with a significant increase in randomness entropy change when the solution is formed, allow this solution to form spontaneously.

Nonpolar vitamins and nonpolar solvents both have weak intermolecular interactions, so the overall enthalpy change energetics is again small. Hence, in the case of nonpolar vitamins dissolving in nonpolar lipid solvents, the small enthalpy change, coupled with a significant increase in randomness entropy change when the solution is formed, allow this solution to form spontaneously as well.

For a nonpolar vitamin to dissolve in water, or for a polar vitamin to dissolve in fat, the energy required to overcome the initial intermolecular forces i. Hence, in these cases, the enthalpy change energetics is unfavorable to dissolution, and the magnitude of this unfavorable enthalpy change is too large to be offset by the increase in randomness of the solution. Therefore, these solutions will not form spontaneously.

There are exceptions to the principle "like dissolves like," e. In general, it is possible to predict whether a vitamin is fat-soluble or water-soluble by examining its structure to determine whether polar groups or nonpolar groups predominate.

In the structure of calciferol Vitamin D 2 , shown in Figure 3 below, we find an -OH group attached to a bulky arrangement of hydrocarbon rings and chains.

This one polar group is not enough to compensate for the much larger nonpolar region. Therefore, calciferol is classified as a fat-soluble vitamin. Although the molecule has one polar hydroxyl group, it is considered a nonpolar fat-soluble vitamin because of the predominance of the nonpolar hydrocarbon region. Structures and Functions of Vitamins Table 1, below, shows the structures and functions of several fat- and water-soluble vitamins.

To view a larger representation of the 2D and 3D structures, click on the name of the vitamin. To view and rotate the vitamin molecules interactively using RASMOL , please click on the three-dimensional structures for the coordinate. Coenzyme for collagen connective tissue protein formation; antioxidant; antibody production; hormone synthesis; cholesterol formation and excretion Calciferol Vitamin D 2.

Calcium and phosphorus absorption and regulation needed for bone, teeth, and proper nerve function ; some role in insulin secretion Pantothenic Acid Part of the Vitamin B Complex.

Release of energy from food; manufacture of coenzyme A needed for breakdown of fats and carbohydrates; production of neurotransmitters; hemoglobin production Pyridoxine Vitamin B 6.

Release of energy from food; synthesis and breakdown of amino acids; prostaglandin manufacture needed for blood pressure regulation and heart function ; skin and hair maintenance; hormone production Retinol Vitamin A.

Vision; growth and repair of epithelial cells; embryonic development; production of myelin nerve coating and other membranes; immune system enhancement. Riboflavin Vitamin B 2. Tissue respiration; metabolism of carbohydrates, amino acids, and fats; growth and repair of body tissues; blood cell development and iron metabolism a -Tocopherol Vitamin E. Antioxidant protects cells from toxic compounds, heavy metals, radiation, and free radicals ; retinal development; protects vitamin A in eyes Table 1 The 2D representations shown in this table were drawn using CS ChemDraw Pro, and the 3D coordinates were obtained by MM2 minimization using CS Chem3D Pro.

Note: The 2D and 3D representations for each vitamin are drawn from the same view. The 3D but not the 2D representations are all drawn to the same scale. In the 3D representations, carbon atoms are gray, hydrogen atoms are light blue, oxygen atoms are red, and nitrogen atoms are dark blue. Olestra and Vitamin Solubility The solubility properties of vitamins determine how well they will be absorbed by the body. Water-soluble vitamins can easily enter the bloodstream by diffusion, since the stomach contents, extracellular fluid, and blood plasma are all aqueous solutions.

Fat-soluble vitamins must be consumed together with dietary fat to be absorbed. The vitamins are first dissolved in the dietary fat. Then, bile released from the gall bladder acts like a detergent and allows the fat with the vitamins dissolved in it to be solubilized in micelles. Recall the discussion of detergents and micelles from the "Membranes, Proteins, and Dialysis" experiment.

However, some newly-developed food products, unfortunately, have been found to disrupt this pathway for absorbing fat-soluble vitamins in the body. In recent years, many types of "fat-free" foods have come into the marketplace. One such type of these foods contains artificial fats that are substituted for the natural fats and oils found in the foods. These artificial fats add no fat or calories to the diet, because they are not digested or absorbed by the body.

The main artificial fat commercially in use is Olestra. Olestra is marketed under the name Olean by Proctor and Gamble, Inc. It is a synthetic sucrose ester that is not digested or absorbed by the body. How does this work? Olestra, like natural fat, has nonpolar hydrocarbon chains. But whereas fat has only three such chains attached to a glycerol molecule and thus is known as a " triglyceride " , Olestra contains eight such chains attached to a sucrose molecule.

Refer to the figure on membrane structure in the "Membranes and Proteins" experiment for the structure of glycerol. To digest natural fats in the body, lipase an intestinal enzyme that breaks down lipid molecules removes the hydrocarbon chains from the glycerol.

The hydrocarbon chains are then emulsified incorporated into micelles with bile, and absorbed into the bloodstream. Because Olestra has so many hydrocarbon chains, there is not enough room for lipase to reach the place where they are attached to the sucrose, and so the side chains cannot be removed.

Therefore, the nonpolar Olestra molecule is too large to form absorbable micelles, so it passes through the intestinal tract, undigested and unabsorbed by the body. Olestra has been approved by the FDA for use in savory snacks, such as potato chips. Unfortunately, Olestra may not be as healthy as it first sounds. It has been shown to cause gastrointestinal symptoms including abdominal discomfort, flatulence, and changes in stool consistency.

More importantly, it interferes with the absorption of fat-soluble vitamins from food when present in the small intestine at the same time as other foods.