Chapter 12 Effects of the Menstrual Cycle on the Acquisition of Peak Bone Mass

1. Chapter 12Effects of the Menstrual Cycle on the Acquisition of Peak Bone Mass Mimi Zumwalt, MD

2. Learning Objectives • Learn about the reproductive anatomy and physiology of the normal menstrual cycle • Delineate the constituents/function of bone, its biochemistry, physiology, and metabolism • Understand the interaction between female sex hormones and components of bone • Recognize the importance of peak bone mass achievement, its definition, and methods of optimal attainment • Comprehend the effects of abnormal menses on peak bone mass, bone density, how to minimize bone loss and enhance bone gain

3. Introduction • Skeleton provides structural support for body • Bone is dynamic tissue • Maximizing bone building important in growing years • Better to have higher peak bone mass to protect against later bone loss

4. Female Sex Organ Anatomy & Menstrual Cycle Physiology • Uterus, ovaries, & accessory organs • Eggs & sex hormone production • Estrogen & progesterone • Hypothalamic-pituitary-ovarian (HPO) axis • GnRH, FSH, LH • Monthly menstrual cycle • Follicular, ovulatory, & luteal phases

5. Female Sex Hormones & Bone • Estrogen • “Set point” for bone mass • Coupling effect • Long bone longitudinal growth • Progesterone • Synergistic w/estrogen on bone

6. Bone Composition, Physiology, Function & Interaction w/Ovarian Hormones • Bone cells osteoblasts & osteoclasts • Formation coupled w/resorption • ~99% of body’s calcium in bone • Needs vitamin D for absorption • Estrogen essential as well • Menstrual irregularity affects bone loss from not enough hormonal influence

7. Peak Bone Mass • PBM mostly achieved during teenage years, especially around “adolescent growth spurt” • Maximum ~mid-twenties • 0.3% loss per year after until mid-forties • Genetics & environmental influence • Nutrition, mechanical loading thru exercise, hormonal milieu/menses • 2% loss/yr if not balanced

8. Abnormal/Absent Menstrual Cycle & Peak Bone Mass • Secondary amenorrhea • Pregnancy, endocrine, anatomic, tumors • Female athlete triad • Premature osteoporosis • Gymnastics only partial offset • Gynecologist consult • DEXA “gold standard” • Serum & urine markers of bone metabolism

9. Conclusion • Maximizing PBM essential especially during adolescent growth spurt • Regular menses important for building bone • Appropriate exercise & adequate nutrition (calcium & vitamin D) pertinent as well • High PBM helps w/bone loss later in life

10. Case Study • You are a primary care sports medicine physician in a multi-specialty group practice consisting of pediatrics, internal medicine, OB/GYN, and family physicians. For the past few years, you have been the team physician for local high school athletes, including track and field events and other court sports. Lately, the team athletic trainer has brought in a few of the female long distance runners with similar complaints of vague, aching pain in their feet and legs, especially after a couple of weeks’ practice, e.g., running around the track. Upon further questioning, these female athletes also reveal that their menses have been very irregular and/or absent over the last year or so.