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Essential Minerals: Calcium Functions, Absorption & Deficiency

Learn about calcium, the most abundant mineral in the body. Understand its functions, absorption process, factors affecting absorption, maintenance of serum levels, causes of hypocalcemia, and hypercalcemia. Gain insights into calcium deficiency symptoms, including tetany and Chvostek’s sign.

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Essential Minerals: Calcium Functions, Absorption & Deficiency

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  1. Minerals Dr Reed Berger Nutrition Course Director Visiting Clinical Professor GI/Nutrition

  2. General Lecture Format • -test questions will come from clinical correlations--these will be relevant in clinical training and practice • -items with *** and those with photos are important!!

  3. Minerals • A naturally occurring , homogeneous, inorganic substance required by humans in amts of 100 mg/day or more • -functions • -high and low serum levels • -absorption • -excretion • -deficiency • -toxicity

  4. calcium

  5. Calcium -most abundant mineral in the body -99% of calcium is in the bones and teeth -the remaining 1% is in the blood and ECF in cells and soft tissues

  6. Skeletal Calcium -if there is no reserve, calcium is drawn from bone—leading to deficiency

  7. Serum levels: 8.8 to 10.8 mg/dl • **when albumin is low (malnutrition, liver dz), calcium is decreased • Ratio: for each gram albumin is decreased below 4, add 0.8 to calcium

  8. -ionized calcium is increased in acidosis and decreased in alkalosis (increased bicarb binds calcium) • ***-example: in resp alkalosis, total serum calcium is normal, but ionized is low—always check ionized level with acid/base disorders

  9. Functions • -building and maintaining bones and teeth • -transport fxn of cell membranes and membrane stabilizer • ***-nerve transmission and regulation of heartbeat—use calcium gluconate IV to treat hyperkalemia (EKG—peaked T waves) • -ionized form initiates formation of the blood clot • -cofactor in conversion of prothrombin to thrombin

  10. Absorption • -***absorbed mainly in the acidic part of the duodenum • -absorption is decreased in the lower GI tract which is more alkaline • 20-30% of digested calcium is absorbed • Absorption is thru 1,25 (OH)2D3 (vit D derivative)--stimulates production of calcium binding protein and alk phos • -unabsorbed form is excreted in feces

  11. Factors that increase calcium absorption • -***more efficiently absorbed when the body is deficient • -best absorbed in acidic environment (upper duodenum) • -HCL in stomach allows better absorption in the proximal duodenum • -taking calcium with food increases abs • -fat increases intestinal transit time and increases absorption

  12. Factors that decrease absorption • -***lack of vitamin D • -oxalic acid forms insoluble complex which decreases absorption (rhubarb, spinach, chard, beet greens) • -phytic acid found in outer husks of cereal grains also form insoluble complex • -alkaline medium decreases abs.(lower GI tract) • Aging decreases absorption

  13. Maintenance of serum level • -parathormone (PTH) by the parathyroid gland and thyrocalcitonin secreted by the thyroid gland maintain serum levels • -***with decreased serum calcium levels, PTH increases and causes transfer of calcium from bone to blood to increase serum levels • -decreased levels also cause kidney to reabsorb calcium more efficiently (might normally be excreted in the urine) and to increase intestinal absorption • -when blood levels are increased, calcitonin acts by the opposite mechanisms as PTH to decrease serum levels

  14. Maintenance of serum level cont’d • ***-always need to correct low Mg level before treating a low calcium level • -hypomagnesemia decreases tissue responsiveness to PTH

  15. Causes of hypocalcemia -***malabsorption -small bowel bypass, short bowel -vit D deficiency -alcoholism -***chronic renal insufficiency -***diuretic therapy

  16. Causes of hypocalcemia cont’d -hypoparathyroidism -***hypomagnesemia -sepsis -pseudohypoparathyroidism -calcitonin secretion with medullary carcinoma of the thyroid

  17. Causes of hypocalcemia cont’d -***associated with low serum albumin (ionized calcium will be wnl) -decreased end organ response to vit D -hyperphosphatemia -***aminoglycosides, plicamycin, loop diuretics, foscarnet

  18. Causes of hypercalcemia -milk-alkali syndrome -vit D or vit A excess -primary hyperparathyroidism -secondary hyperparathyroidism (renal insuff, malabsorption) -acromegaly -adrenal insufficiency

  19. Causes of hypercalcemia cont’d ***Neoplastic Disease -tumors producing PTH-related proteins (ovary, kidney, lung) -***mets to bone -lymphoproliferative disease including multiple myeloma -secretion of prostaglandins and osteolytic factors

  20. Causes of hypercalcemia cont’d -***thiazide diuretic -sarcoidosis -paget’s disease of bone -***immobilization -familial hypocalciuric hypercalcemia -complications of renal transplant -iatrogenic

  21. Excretion • -normal is 65-70% of ingested calcium to be excreted in the feces and urine • -strenuous exercise increases loss (in sweat) • -***immobility with bed rest and space travel increase calcium loss because of lack of bone tension

  22. RDA • -see handout

  23. sources

  24. Deficiency • 1)***bone—to be discussed in osteoporosis lecture • 2) tetany—decreased serum levels increase the irritability of nerve fibers resulting in muscle spasms, fatal laryngospasm • ***-Chvostek’s sign: contraction of the facial m. after tapping the facial n. • ***-Trousseau’s sign: carpal spasm after occlusion of the brachial a. with blood pressure cuff for 3 min • 3) HTN—controversial • 4) prolonged QT--arrythmias

  25. Toxicity • -***polyuria, constipation, bone pain, azotemia, coma • -”stones, bones(bone pain), groans, psychiatric overtones”

  26. Phosphorus • Levels maintained by parathyroid gland

  27. Functions • -structure of teeth and bones • -essential component in cell membranes, nucleic acids, phospholipids • -phosphorylation of glucose • -buffer system in ICF and kidney

  28. absorption -best occurs when calcium and phos are ingested in equal amts (milk) -vit D also increases absorption

  29. RDA • -see table (and for all RDA’s)

  30. sources

  31. Sources ***dietary sources should be restricted in renal disease (usually see increased phos, decreased Ca) • -protein sources • -meat, poultry, fish, eggs, legumes, nuts, milk, cereals, grains

  32. Renal Disease

  33. Causes of hypophosphatemia -starvation -TPN with inadequate phos content -malabsorption, small bowel bypass -vit D deficient and vit D resistant osteomalacia

  34. Causes of hypophosphatemia cont’d -phosphaturic drugs: theophylline, diuretics, bronchodilators, corticosteroids -hyperparathyoidism (primary or secondary) -hyperthyroidism -renal tubular defects -hypokalemic nephropathy -inadequately controlled DM -***alcoholism

  35. Causes of hypophosphatemia cont’d Intracellular shift of phosphorus -administration of glucose -anabolic steroids, estrogen, OCP -respiratory alkalosis -salicylate poisoning Electrolyte abnormalities -hypercalcemia -hypomagnesemia -metabolic alkalosis

  36. Causes of hypophosphatemia cont’d Abnormal losses followed by inadequate repletion -***DM with acidosis—with aggressive therapy -***recovery from starvation or prolonged catabolic state—refeeding syndrome -***chronic alcoholism, especially with nutritional repletion, assoc with hypomagnesemia—” -recovery from severe burns

  37. Causes of hyperphosphatemia -excessive growth hormone (acromegaly) -hypoparathyroidism assoc with low Ca -pseudohypoparathyroidism assoc with low Ca -***chronic renal insufficiency -acute renal failure

  38. Causes of hyperphosphatemia cont’d Catabolic states, tissue destruction -stress or injury, rhabdomyolysis (esp with renal insufficiency) -chemotherapy of malignant disease, particularly lymphoproliferative disease Excessive intake or absorption -laxatives or enemas containing phosphate -hypervitaminosis D

  39. Deficiency • -fatal • -usually rare with food intake • -***respiratory muscle collapse • -heart failure • -muscle aches, bone pain, and fracture

  40. Toxicity • -symptoms of the primary disorder

  41. Magnesium

  42. Function -bone, muscle contractility, nerve excitability -antagonistic to calcium --in a muscle contraction, Mg relaxes, and calcium contracts --low Mg can cause pregnancy induced HTN

  43. Absorption / Excretion • -absorption varies • -similar to calcium (low pH, upper GI), however, no Vit D required-kidney conserves Mg when intake of Mg is low • -large losses with vomiting because of high levels of gastic juice

  44. sources

  45. Sources • -seeds, nuts, legumes, unmilled cereal grains, dark greens • -fish, meat, milk, fruits • -lost during refining of flour, rice, vinegar

  46. Causes of hypomagnesemia -malabsorption, chronic diarrhea, laxative abuse -prolonged GI suction -small bowel bypass -malnutrition -***alcoholism -refeeding -TPN with inadequate Mg

  47. Causes of hypomagnesemia cont’d -DKA -diuretics -hyperaldosteronism, Barrter’s syndrome -hypercalcuria -renal Mg wasting -hyperparathyroidism -postparathyroidectomy -vit D therapy -aminoglycosides, ***cisplatin, ampho B

  48. Causes of hypermagnesemia Decreased renal fxn ***Increased intake—abuse of Mg containing antacids (MOM) and laxatives in renal insufficiency

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