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. Vitamin D is needed for the assimilation of calcium. vitamin C, vitamin E, vitamin K, magnesium, and boron
Advertisements
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.
| | | | |

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.
| | | | |
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.
| | | | |
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.
Advertisements

Related topics in nutritional deficiency diseases:
.
.
.
.
.
.
.
.
.
.


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/


Interesting topics in nutritional deficiency diseases:
.
.
.
.
.
.
.
.
.
.


Current topic on nutritional deficiency diseases: Calcium intake and absorption.