Calcium

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Bottom line: 1000-1500mg per day; 3 servings of dairy.

Basics

  • One of the essential minerals
  • deficiency of calcium can lead to osteoporosis
  • an important component of bone (hydroxlapatite)
  • Intracellular calcium plays a crucial role in cellular metabolism, in the transmission of nervous impulses, muscular contraction and as an important intracellular signalling molecule

To identify the roles of calcium and vitamin supplementation, exercise and hormone replacement therapy in ameliorating osteoporosis

Role

  • The average adult human body contains about 1 kg of calcium
    • 99.9% is in the form of hydroxy apatite in the skeleton
    • Of the remaining 1g:
      • ~700mg is in the extracellular interstitial space
      • ~300mg is in blood
        • ~40% is protein bound
        • 40% is free and in the ionized form
        • the remainder is found complexed to other ions
      • 40 mg is found within cells

Dietary sources

  • Found in milk and dairy products, sardines, clams and oysters, kale and collard, turnip greens, mustard greens and broccoli (it is also high in spinach but remains bound tightly to oxalic acid)
  • The Recommended Daily Intake (RDI) varies with age:
    • 1000 - 1500mg per day is now recommended by the Osteoporosis Society of Canada (three or more servings of dairy products)
    • more for children and adolescents
    • Intakes up to 2000mg per day are regarded as safe
    • For some, supplementation is necessary
    • Supplements should be pure and absorbable

Metabolism

  • Absorbed by two types of intestinal transport:
    1. carrier-based
      • depends on a cellular transport system
      • saturable, dependent on vitamin D
    2. passive, paracellular and diffusion-based
      • only dependent on the concentration of the mineral in the digesta
  • Calcium is borrowed from the skeleton if not available in sufficient quantities
  • This is one of the potential mechanisms for osteoporosis


Resources