Showing posts with label absorption. Show all posts
Showing posts with label absorption. Show all posts

Calcium intake - Calcium absorption

› › › Calcium intake and absorption

Calcium intake

Calcium absorption by the intestines and its utilization by the body depends upon many factors.
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Vitamin D is needed for the assimilation of calcium. vitamin C, vitamin E, vitamin K, magnesium, and boron also assist in the assimilation of the mineral. Large doses of calcium ingested at a time will get wasted. In large quantities much of the mineral will get excreted by the body. For better calcium absorption, less than 500 mg must be consumed at a time and its consumption must be spread out throughout the day to get the daily requirement.

Calcium absorption

Calcium absorption occurs by both active transport as well as passive paracellular transport in the small intestines. When the nutritional status of the mineral is high, the mineral is taken up through passive paracellular transport in the jejunum and ileum parts of the intestine. Passive transport is independent of Vitamin D level in the body. When the mineral ingestion is low, active transport of the mineral into the body becomes the primary pathway and much of the incorporation takes place across the brush border membrane in the duodenum portion of the intestine.
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The entry of the mineral into the enterocytes from the apical side is regulated by calcium channel TRPV6. Expression of TRPV6 is vitamin D dependent in humans. Calbindin-D9k, a vitamin D-dependent calcium-binding S-100 protein, is present in the intestinal epithelial cells (enterocytes). It is coded by S100G (CALB3) gene. The active vitamin D metabolite, calcitriol stimulates the calbindin-D9k expression.
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Calbindin-D9k increases the absorption of Ca2+ by buffering the ions in the cytoplasm. It mediates in the transport of the mineral across the enterocyte to the basolateral side by stimulating the adenosine triphosphate (ATP) dependent taking in of Ca2+ ions into duodenal basolateral membrane vesicles. Calbindin-D9k stimulates the basolateral calcium-pumping ATPs. Calcium pumps such as PMCA1 utilize intracellular ATP to pump calcium into the intercellular fluids.

What impairs the absorption of calcium

Many factors like old age, excessive consumption of sodium, proteins, alcohol and caffeine, prolonged corticosteroid therapy, food containing phytic acid and oxalic acid can impair calcium absorption and/or increase its excretion from the body.
Age related malabsorption
Children and young adults can assimilate as much as 50% of the ingested calcium. However this capability decreases with aging. Hence in middle-age and old age more supplements has to be ingested to make up for the poor absorption. Further there is increased bone turnover loss of the mineral in old age.
Alcohol
Alcohol reduces assimilation of this mineral and increases its excretion. It can also interfere with the production of enzymes in the liver for vitamin D metabolism. The diuretic effect of alcohol causes loss of many minerals by urinary excretion from the body.
Caffeine
Caffeine reduces absorption of this mineral and increases its urinary excretion as well as fecal excretion. The excessive consumption of caffeine containing drinks like coffee, tea and cola drinks hampers the assimilation of the mineral.
Oxalate and phytates
Phytic acid and oxalic acid found in some plant sources of food binds to the calcium, inhibiting its assimilation. Spinach, chard, collard greens, chocolate and sweet potatoes are high in oxalic acid.
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Whole grain products, beans, seeds and soy isolates are rich in phytic acid. For better absorption of the mineral the above foods may not be taken along with supplements.
Sodium, protein and dietary fiber
Foods containing high levels of sodium or protein interfere with assimilation of the mineral. Further they cause more calcium to be lost in urine. Fiber from sources like wheat bran can bind the mineral to the intestinal tract. Excess soluble fiber can reduce the absorption of calcium.
Medications
  • Administering intravenous ceftriaxone (Rocephin) along with calcium supplements can be life threatening.
  • Quinolone antibiotics like ciprofloxacin, levofloxacin and ofloxacin can decrease the assimilation of the mineral.
  • Tetracycline antibiotics can bind to this mineral and decrease efficacy of both the antibiotic as well as the mineral.

How to optimize calcium absorption

  • Sufficient exposure to sunlight and vitamin D supplementation can help in increasing the assimilation by the body.
  • The quantity of Ca consumed at a time should not exceed 500 mg to reduce loss in fecal excretion.
  • Eating the supplements along with food help in stomach acid acting on the mineral to increase its absorption.
  • For better absorption of the mineral, calcium binding foods may not be taken along with the supplements or food rich in calcium.
  • Avoid excessive consumption of alcohol, caffeine and sodium.
  • According to a study from Purdue University, consuming honey along with supplements enhanced calcium assimilation.
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References:
1.http://www.health.gov/dietaryguidelines/dga2005/document/html/AppendixB.htm#appB4
2.http://www.health.gov/dietaryguidelines/dga2005/document/html/AppendixB.htm#appB5
3.http://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/

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Current topic on nutritional deficiency diseases: Calcium intake and absorption.
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Organic selenium - Selenium absorption and metabolism

Home > Organic selenium - absorption and metabolism

Organic selenium is the best form of this trace mineral with better absorption and metabolism.

This essential trace mineral exists in its organic and inorganic forms.
Its natural form shows higher degree of absorption and metabolism than the inorganic form.
It is the integral part of the selenoprotein and antioxidant enzyme, glutathione peroxidase (GPx), and is vital for reducing the destruction of cells in free radical peroxidative reactions.

What is organic selenium?

Though it rarely exists in its elemental form, its inorganic salts are present in soil.
Its selenite and selenate salts are obtained as by-product of copper mining.
Plants take up these salts by absorption and transform them into amino acids like selenomethione and selenocysteine.
Selenium utilization in plants is similar to that of sulphur and the trace minerals are found together.
From the sulphate salts in the soil, plants make the amino acid methionine and from selenite and selenate salts they make L-selenomethionine.
Till the advent of enriched yeast production, the sources of this trace mineral were from plant foods and inorganic supplements like sodium selenite (Na2SeO3) and sodium selenate (Na2SeO4).

Types of organic selenium forms

L-selenomethionine: Great proportion of seleno amino acids from food sources exist in this form.
This type of selenium has good rate of utilization in the body.
D-selenomethionine: This is an isomer of L-selenomethionine and found in small quantities in food.
L-selenocysteine: Formed due to substitution Se instead of sulfur in the amino acid cysteine.
This form is found in small quantities in food.
D-selenocysteine: Very small quantity of this isomer is found in food.
Selenium yeast: Properly fed-batch fermented yeast contains high concentration of L-selenomethionine and small quantities of L-selenocysteine.
L-Se-methylselenocysteine: This compound is found in Brassica (broccoli, cauliflower) and Allium (onion, garlic) plant families.
This is now synthesized from chemicals and found to be non-toxic.
It is found to be effective in the treatment of cancers.

Comparison of organic selenium and inorganic salts for their absorption and metabolism

The absorption of inorganic selenate salts is fast but they are excreted with same speed without much utility to the body.
The metabolism of selenite salts poor and only up to 50% is utilised.
However it is retained in the body for some time.
The utilization rates of selenomethionine in the intestinal tract are high (19% better than selenite) as it is recognized as an amino acid by the body.
This form is well retained and utilized in the body.

Superiority of selenomethionine from organic selenium sources over synthetic products

Christine D Thomson, Alexandra Chisholm, Sarah K McLachlan and Jennifer M Campbell from the Department of Human Nutrition, University of Otago, Dunedin, New Zealand conducted a study on comparative absorption, metabolism and bioavailability of selenium from natural sources and synthetic sources.
It was proven beyond doubt in this experiment that the food form of selenomethionine absorption and metabolism is much better than the synthetic chemical form.
In order to have sufficient regulated supply of this trace mineral in our body, it is best advised to obtain Selenium from food sources, wherein the absorption and metabolism are better.
Related topics on selenium foods and supplements:
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Brazil nuts.
Selenium health benefits.
Selenium food sources.
Sodium selenite - Sodium selenate.
Selenium yeast.
Selenomethionine.
Organic selenium - absorption and metabolism (current topic).
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Calcium absorption

Calcium absorption by body is regulated by many factors.
Calcium is stored in the body in the bones making up 99% of the mineral. The rest of the 1% is found in the body fluids.
This mineral is available through food and is absorbed and used for the growth and repair of bones and some of it is excreted in urine.
Parathyroid hormone regulates the availability in serum and if required sourcing it from the bone mass.
For the mineral to get sufficiently absorbed from intestine, vitamin D plays an important role by increasing the binding proteins.
The best source is milk and milk products and calcium through this source is absorbed excellently.
Sea weeds like kelp, almonds, beans, sesame, figs and oranges are some of the natural sources essential minerals.
Supplements are available in many forms and mostly with added vitamin D.
Health specialists recommend 1250 mg of elemental calcium per day split in to two or three doses for adults.
Its absorption decreases with one time dose of 500mg and above and hence the advice of splitting the dose.
Supplements in the form of calcium carbonate (CaCO3) are the most common and are the least expensive.
Antacids also contain CaCO3 and they can be used effectively as supplements if they contain predominant amount of available mineral.
Calcium citrate and phosphate are other useful supplements available but are expensive.
Supplements like calcium lactate and gluconate apart from being expensive contain less of elemental calcium.
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