Osteoporosis

Osteoporosis is characterized as a thinning of skeletal tissue that occurs due to a substantial loss of hydroxyapatite crystals and bone matrix proteins. This phenomenon results in a weakened skeleton that is more prone to debilitating fragility fractures-the ultimate outcome that lifestyle strategies including diet and exercise aim to prevent. Osteoporosis is defined as “a skeletal disorder characterized by compromised bone strength, predisposing to an increased risk of fracture.”1 The emphasis is on compromised bone strength, and recognition that bone strength is altered by both the quantity and quality of a skeletal site. Bone quantity is routinely measured clinically as bone mineral density (BMD) by dual-energy X-ray absorptiometry, whereas bone quality is more challenging to assess but includes consideration of how mineral and matrix proteins are integrated to result in structurally

5.1 Introduction .................................................................................................. 211 5.2 Molecular Etiology of Osteoporosis ............................................................. 212

5.2.1 Mechanisms of Bone Loss ................................................................ 212 5.2.2 Prevention of Bone Loss ................................................................... 213

5.3 Dietary Mechanisms Underlying Prevention of Osteoporosis ..................... 215 5.3.1 Estrogen Receptor-Mediated Pathways: Isoflavones ....................... 215 5.3.2 Aryl Hydrocarbon Receptor: Resveratrol, Isoflavones ..................... 216 5.3.3 Bone Morphogenetic Protein Signaling: Soy Foods, Hesperitin ...... 216 5.3.4 Wnt/β-catenin Signaling: Blueberry, Resveratrol ............................. 217 5.3.5 Peroxisome Proliferator-Activated Receptors: Fatty Acids ............. 218 5.3.6 Inflammation and Reactive Oxygen Species .................................... 218 5.3.7 Prostaglandins and Fatty Acids ........................................................ 219 5.3.8 Antioxidant Activity and Collagen Synthesis: Vitamin C ................220 5.3.9 Vitamin D Receptor Pathway ........................................................... 221 5.3.10 Dietary Insufficiencies ...................................................................... 222

5.4 Physical Activity Mechanisms Underlying Prevention of Osteoporosis ...... 222 5.5 Recommendations ........................................................................................224