Physical Activity and Bone Health during Childhood and Adolescence: Critical Periods for the Prevention of Osteoporosis Suggested Links (click below) htm Kathleen Janz

Kathleen Janz Department of Health and Sports Studies, University of Iowa, United States of America My work centers on the health aspects of physical activity and fitness, particularly during childhood and adolescence. Currently, I am working on a longitudinal study with colleagues from Dentistry, Medicine, and Public Health to examine how genetics, diet, and physical activity influence bone growth in children. A thorough understanding of bone development may allow for interventions to prevent bone diseases from occurring at the earliest possible ages, when such interventions are most likely to be effective. Since physical activity is a modifiable factor, understanding its effects on bone accretion would be particularly useful in the construction and implementation of disease prevention strategies.

Learning Objectives: Physical Activity and Bone Health To understand the worldwide scope and severity of osteoporosis To view osteoporosis as a disease with pediatric origins To understand the bone adaptation process during childhood and adolescence To appreciate the contribution of physical activity as a behavioral determinant of children’s bone health

Performance Objectives: Physical Activity and Bone Health To identify the determinants of bone development in children and adolescents To interpret common bone measures in relationship to osteoporotic risk To prescribe the most appropriate type of activities for strengthening bone in children and adolescence

Osteoporosis Most Common Human Bone Disease Low Bone Mineral Mass and Structural Deterioration Susceptibility to Fractures  Spine, Hip, Wrist

Osteoporosis: Porous Bone 75 Yr Old (Normal) Vs. 47 Yr Old (Osteoporosis)

Scope and Severity of Osteoporosis 30 to 40% Lifetime Risk for Fracture in Women 13% Lifetime Risk for Fracture in Men Incidence Rates are Increasing Developed Countries Higher Rates 30% Hip Fractures Do Not Go Home (US) 20% Persons with Hip Fractures Die in a Year (US)

Measuring Bone Mineral Content Bone Mineral is Calcium, Phosphate, and Hydroxide Dual X-Ray Absorptometry (DXA) Measures Bone Mineral Content DXA Adjusts Mass for Area (Areal Bone Mineral Density or aBMD)

WHO Areal Bone Mineral Density Categories: T Scores Normal Bone Mineral Density 1 SD Average, Young, White Female Low Bone Mineral Density (Osteopenia) 1 to 2.5 SD Below Average, Young, White Female  X Fracture Osteoporosis = Greater than 2.5 SD Below  5 X Fracture

Healthy Bones?

Systemic Sex Hormones, Growth Hormones, Calcium, Vit. D, Smoking, & Others Local Gravitational Forces and Muscular Forces Genetic Factors Race, Body size, Others Bone Reacts to Systemic and Local Factors

Osteoporosis Originates during Childhood Level of Bone Mass during Childhood and Adolescence Influences Fracture Risk Peak Bone Mass Probably Most Important Population Factor Peak Bone Mass Nearly Complete Teens and Twenties 10% Increase Peak Bone Mass May Reduce Fracture Risk by 50%

Natural History of Bone Childhood New Bone Added Faster than Old Bone Removed Peak Bone Mass Bone Resorption Exceeds Bone Formation Rapid Loss Menopause 3-6 yrs From: Kemper, Pediatric Exercise Science 2000;12:

Areal bone mineral density gains in femoral neck during puberty. From Theintz et al., J Clin Endocrine Metab 1992; 75: Bone Increases Rapidly During Puberty aBMD g/cm 2

Physical Activity is Important for Optimizing Peak Bone Mass Muscular Forces Strength Building Gravitational Forces Weight-bearing Intensity (Strain) More Important than Duration

Bone Responds Best to High Load Activities in Unusual Patterns Site-specific Response E.g., Dominant Arms of Racquet Sport Players Optimal Load Different than Long Duration and Low Intensity for Heart Health

Evidence Supporting Physical Activity as an Important Behavioral Determinant of Bone Development

Total body and femoral neck peak bone mineral accrual velocity (g/yr) by inactive, average, and active physical activity groups for girls and boys. From Bailey et al., J Bone Miner Res 1999; 15:

Proximal Femur Bone Mineral Content by Vigorous Activity Quartiles in 5-year-old Children 12%  BMC Least to Most From Janz et al., Pediatrics 2001;107: Adjusted for Age, Weight, Height

Summary of Observational Studies Examining the Relationship of Physical Activity to Bone Measures Most Report Differences Ranging from 2 to 20% between Active and Inactive Most Study Subjects have been Caucasian Only a Few Studies Report Gender Interaction Some Evidence for Physical Activity and Maturation Interaction Problems with DXA

Summary of Intervention Studies Examining the Relationship of Physical Activity to Bone Measures High-load, Weight-bearing Protocols Most Report a Positive Impact of Intervention Bone Measures at Proximal Femur Most Consistently Associated Some Evidence for Physical Activity and Maturation Interaction Intervention Trials Now using DXA and Other Methods

Physical Activity and Bone Health during Childhood and Adolescence Create a Wide Margin of Safety by Optimizing Peak Bone Mass Age-appropriate High Impact Activities Combined with Bone Healthy Diet

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