Role of Nutrients in Skeletal Development and Maintenance

1
Role of Nutrients in Skeletal Development and
Maintenance

• Arline McDonald, Ph.D.
• 20 January 2000

2
Nutrient Requirements of Skeletal Tissue

• Provide structural constituents
• mineral matrix
• organic matrix
• Support metabolic activity
• hematopoiesis

3
Sensitivity of Skeleton to Nutrient Intakes

• Primary effects
• structural
• Secondary effects
• metabolic

4
Structural Role of Nutrients
5
Nutritional Priorities for Skeletal Structural
Integrity
Avoid Alcohol
Protein
No Smoking
Magnesium
Calcium Vitamin D
Phosphorus
Do Physical Activity
Do away with Caffeine
Sodium
6
Calcium Homeostasis
Adult Values
Intestinal 800-1200 mg
Skeletal 1000 mg
Plasma 10 mg/dL

• amount
• bio-availability
• meal components

• Ionized
• protein-bound
• complexed

• Absorbed
• Structural

PTH Vitamin D Calcitonin
Fecal 45-100 mg 70 intake
Renal 100-240 mg
PTH () Phosphorus () Sodium (-)
7
Calcium Accretion
30 mg
1000 mg
TermInfant
Adult
8
Skeletal Mineral Reserves
9
Average Adult Mineral Intake as a of Required
Intake
Nationwide Food Consumption Survey Data
adolescent boys (HI) adult women (LO)
10
Effect of Oral Phosphorus on Fasting Serum 1,25
(OH)2D3
Normal P Intake
Low P Intake
High P Intake
Adapted from J Clin Invest , 1986
11
Magnesium Intake by Food Source
Dairy
Beverages
Meat
Grains
Fruit
Vegetables
12
Effects of Phosphorus and Vitamin D on Calcium
Homeostasis
Ca
D

-
PO4
PTH

Calcitonin
1,25-OH2-D3
-


ECF
Ca 1000 g
GI
Ca1.0 g
Bone
-
PTH
Kidney
13
Lifelong Calcium Deficiency and Bone Fracture Risk
Fracture Risk
14
Calcium/Phosphorus Ratios of Selected Dietary
Calcium Sources
15
Calcium Content of Common Supplements
Solubility
Most
Least
16
Importance of Calcium to Fracture Risk

• Determinant of peak bone mass
• 3rd and 4th decade
• Reduces bone mass loss
• only if intakes are deficient
• 2.5 times fracture risk in men and women over 50
• 470 mg vs 735 mg intakes