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DEMS: Unit III > Dietary Calcium > Flashcards

Flashcards in Dietary Calcium Deck (8)
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Role of calcium in bone health

  • Ca2+ most abundant mineral in body
  • Average adult male has 3lbs of calcium - 1.7% of body weight
  • 99% of Ca2+ is in skeleton
    • 0.7g of skeletal calcium turns over every day
  • Bone Ca2+ turns over about every 5-6 years
  • Extracellular Ca2+ turns over 20-30x/day


3 stages of life when inadequate dietary calcium may lead to increased risk of metabolic disease

  • Premature infants
    • 3rd trimester is period of rapid bone mineral acceleration
    • Preterm infants at risk for "osteopenia of prematurity"
    • Very hard to get proper amount of Ca2+ to preemies in hospital - uterus is just better
  • Adolescence
    • Hormonal milieu during puberty favors calcium absorption and bone deposition
    • ~50% of total adult bone mineral mass accrued during adolescence
  • After skeletal maturity
    • Peri-menopause
    • Associated with relatively high requirements, increased losses, and frequently with low intake


Dietary factors that may adversely impact bone health

  • Lifetime Ca2+ intake helps determine whether or not you can meet your genetic predisposition (70-80% of variability in peak bone mass is genetically determined)
    • Limited ability to adapt to low Ca2+ intake - no protective mechanisms like with iron
  • Protein intake: 
    • Increased protein intake associated with increased Ca2+ absorption and increased urine Ca2+ resulting in net neutral effect
  • Phosphate intake:
    • Increased PTH and increased bone resorption
  • Vitamin D linked to Ca2+ absorption
  • Vitamin K cofactor with osteocalcin and other bone-forming proteins
  • Sodium intake: high Na+ intake --> increased urine Ca2+ excretion
  • Vegetarian diet, with high fruit & vegetable intake (and K+, Mg2+) associated with bone mass preservation
  • Diet low in dairy and high in sodium - not likely to be positive effect
  • Caffeine: increases urine Ca2+ excretion (small effect over a lifetime thank goodness)


Lifestyle factors that may adversely impact bone health

  • Weight-bearing exercise super important - positively relates to bone density
    • Muscle mass directly related to bone mass
    • Active anorexics have higher bone mineral density than sedentary people
  • Smoking/tobacco are bad
  • EtOH is bad --> depresses osteoblasts


Medications/medical factors that may adversely impact bone health

  • Glucocorticoids:
    • Decrease Ca2+ absorption
  • Chronic illness
    • Decrease Ca2+ absorption
  • Hypogonadism decreases estrogen which decreases bone mass
  • Decreased testosterone --> decreased bone mineral density


Strategies to optimize bone density

  • Achieve peak bone mass when you can (i.e. adolescence)
  • Weight bearing activity
  • Maintain good calcium intake over lifetime
    • Benefits of calcium supplementation + vitamin D on fracture reduction and reduced bone loss in subjects >50 years of age
  • Minimize practice that enhance calcium loss &/or bone resorption
    • DASH diet: reduction in Na+ not only associated with reduced BP but also with reduced Ca2+ excretion and bone turnover
    • Mild caution regarding Ca2+ supplementation without vitamin D - associated with increased risk of MI
      • Endocrine society recommends vit D supplementation for fall prevention in elderly
      • At risk of falls: may need 1500-2000 IU vitamin D in addition to adequate calcium


Food sources of calcium 

  • Dairy products: ~70% of Ca2+ in US diet
  • Slight decrease in past few decade because of increased availability of fortified products
  • Need 3 servings/day
  • Milk - 300mg Ca2+
  • Yogurt - 350-450mg Ca2+
  • Cheddar cheese - 200mg Ca2+
  • Canned salmon - 200mg Ca2+
  • Processed tofu - 155mg Ca2+
  • Fortified soy milk - 295mg Ca2+
  • Fortified rice drink - 283mg Ca2+
  • Chopped broccoli - 90mg Ca2+
  • Collard greens - 350mg Ca2+
  • Navy beans - 90mg Ca2+


Calcium supplements

  • Calcium carbonate (TUMS)
    • Max elemental density of Ca2+ per tablet
    • 1250mg tablet = 500mg elemental Ca2+
    • Best absorbed with meals (30%)
    • Has least amount of lead
    • Also includes soft chews like Viactiv (10 cents/chew)
  • Calcium citrate malate
    • Better absorbed without meals (36% absorption)
    • 21% elemental calcium
  • Fortified OJ contains calcium carbonate