Chapter 12Effects of the Menstrual Cycle on the

Acquisition of Peak Bone Mass

Mimi Zumwalt, MDMimi Zumwalt, MD

Learning Objectives• Learn about the reproductive anatomy and Learn about the reproductive anatomy and

physiology of the normal menstrual cyclephysiology of the normal menstrual cycle• Delineate the constituents/function of bone, its Delineate the constituents/function of bone, its

biochemistry, physiology, and metabolismbiochemistry, physiology, and metabolism• Understand the interaction between female sex Understand the interaction between female sex

hormones and components of bonehormones and components of bone• Recognize the importance of peak bone mass Recognize the importance of peak bone mass

achievement, its definition, and methods of achievement, its definition, and methods of optimal attainmentoptimal attainment

• Comprehend the effects of abnormal menses on Comprehend the effects of abnormal menses on peak bone mass, bone density, how to minimize peak bone mass, bone density, how to minimize bone loss and enhance bone gain bone loss and enhance bone gain

Introduction

• Skeleton provides structural support for bodySkeleton provides structural support for body• Bone is dynamic tissueBone is dynamic tissue• Maximizing bone building important in Maximizing bone building important in

growing yearsgrowing years• Better to have higher peak bone mass to Better to have higher peak bone mass to

protect against later bone lossprotect against later bone loss

Female Sex Organ Anatomy & Menstrual Cycle Physiology

• Uterus, ovaries, & accessory organsUterus, ovaries, & accessory organs• Eggs & sex hormone productionEggs & sex hormone production

• Estrogen & progesteroneEstrogen & progesterone• Hypothalamic-pituitary-ovarian (HPO) axisHypothalamic-pituitary-ovarian (HPO) axis

• GnRH, FSH, LHGnRH, FSH, LH• Monthly menstrual cycleMonthly menstrual cycle

• Follicular, ovulatory, & luteal phasesFollicular, ovulatory, & luteal phases

Female Sex Hormones & Bone

• EstrogenEstrogen• ““Set point” for bone massSet point” for bone mass

• Coupling effectCoupling effect• Long bone longitudinal growthLong bone longitudinal growth

• ProgesteroneProgesterone• Synergistic w/estrogen on bone Synergistic w/estrogen on bone

Bone Composition, Physiology, Function & Interaction w/Ovarian

Hormones• Bone cells osteoblasts & osteoclastsBone cells osteoblasts & osteoclasts

• Formation coupled w/resorptionFormation coupled w/resorption• ~99% of body’s calcium in bone~99% of body’s calcium in bone

• Needs vitamin D for absorptionNeeds vitamin D for absorption• Estrogen essential as wellEstrogen essential as well

• Menstrual irregularity affects bone loss Menstrual irregularity affects bone loss from not enough hormonal influencefrom not enough hormonal influence

Peak Bone Mass

• PBM mostly achieved during teenage years, PBM mostly achieved during teenage years, especially around “adolescent growth spurt”especially around “adolescent growth spurt”• Maximum ~mid-twentiesMaximum ~mid-twenties

• 0.3% loss per year after until mid-forties0.3% loss per year after until mid-forties• Genetics & environmental influenceGenetics & environmental influence

• Nutrition, mechanical loading thru Nutrition, mechanical loading thru exercise, hormonal milieu/mensesexercise, hormonal milieu/menses

• 2% loss/yr if not balanced2% loss/yr if not balanced

Abnormal/Absent Menstrual Cycle & Peak Bone Mass

• Secondary amenorrheaSecondary amenorrhea• Pregnancy, endocrine, anatomic, tumorsPregnancy, endocrine, anatomic, tumors• Female athlete triadFemale athlete triad• Premature osteoporosisPremature osteoporosis

• Gymnastics only partial offsetGymnastics only partial offset• Gynecologist consultGynecologist consult

• DEXA “gold standard”DEXA “gold standard”• Serum & urine markers of bone metabolismSerum & urine markers of bone metabolism

Conclusion

• Maximizing PBM essential especially during Maximizing PBM essential especially during adolescent growth spurtadolescent growth spurt

• Regular menses important for building boneRegular menses important for building bone• Appropriate exercise & adequate nutrition Appropriate exercise & adequate nutrition

(calcium & vitamin D) pertinent as well(calcium & vitamin D) pertinent as well• High PBM helps w/bone loss later in lifeHigh PBM helps w/bone loss later in life

Case Study• You are a primary care sports medicine physician in a You are a primary care sports medicine physician in a

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