Dietary Calcium

Question 1

Role of calcium in bone health

Answer 1

• 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

Question 2

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

Answer 2

• 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

Question 3

Dietary factors that may adversely impact bone health

Answer 3

• 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)

Question 4

Lifestyle factors that may adversely impact bone health

Answer 4

• 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

Question 5

Medications/medical factors that may adversely impact bone health

Answer 5

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

Question 6

Strategies to optimize bone density

Answer 6

• 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

Question 7

Food sources of calcium

Answer 7

• 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+

Question 8

Calcium supplements

Answer 8

• 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