628 PART 4 Nutrition for Health and Fitness

Height BOX 24-2

Common MedicationsThat Increase Calcium Loss and

Promote Risk of Osteoporosis

Phenytoin (Dilantin) PhenobarbitalThyroid hormoneCorticosteroidsLasix and thiazide diureticsMethotrexate Cyclosporine Lithium TetracyclineAluminum-containing antacids

HeparinPhenothiazine derivatives

40 60 70 Age BOX 24-3FIGURE 24-9 Normal spine at age 40 and osteoporotic changes at ages 60 and 70. These changes can cause a loss of as much as 6 to 9 in in height and result in the so-called dowager's hump (far right) in the upper thoracic vertebrae.(From Ignatavicius D, Workman M: Medical-surgical nursing:critical thinking for collaborative care, ed 5, Philadelphia,2006, Saunders).

Etiology

Osteoporosis is a complex heterogeneous disorder of un- known etiology, but many risk factors contribute to this condition over a lifetime. Although the fracture-precipitat-ing condition of low BMD is common to all types of osteo- porosis, an imbalance between bone resorption and forma- tion results from an array of etiologic factors characteristic of each form of this disease.

Loss of bone mass to a degree that produces fractures can result from: (1) an excessive acceleration of resorption, espe- cially after the menopause; or (2) a suboptimal peak bone mass that results in bone after the menopause (or later in life in males) that becomes fragile and susceptible to fracture.

The Pathophysiohgy and Care Management Algorithm, Parathy- roid Hormone-Mediated Post-Menopausal Bone Osteopo- rosis, lists several risk factors and illustrates different scenarios of older or younger postmenopausal women that lead to os- teoporotic fractures. Risk factors for osteoporosis include age, race, gender, and factors noted in Box 24-4.

Race and Ethnicity

Whites and Asians suffer more osteoporotic fractures than blacks and Hispanics, who have a greater bone density (Siris et al, 2001). Hypovitaminosis D with secondary hyperpara- thyroidism occur more often in the black population. Thin women, particularly of northern European extraction, are more at risk of osteoporosis than heavier women.

Medical Conditions That DepleteCalcium and Promote Risk of Osteoporosis

HyperthyroidismDiabetesChronic renal failureScurvyChronic diarrhea or intestinal malabsorptionHyperparathyroid diseaseChronic obstructive lung diseaseSubtotal gastrectomyHemiplegia

Menstrual Status

Loss of menses at any age is a major determinant of osteo- porosis risk in women. Acceleration of bone loss coincides with the menopause, either natural or surgical, at which time the ovaries stop producing estrogen. Estrogen re- placement therapies have been shown to conserve BMD and reduce fracture risk within the first few years follow- ing the menopause, at least in short-term studies.

Any interruption of menstruation for an extended pe-riod results in bone loss. The amenorrhea that accompa- nies excessive weight loss seen in patients with anorexia nervosa or in individuals who participate in high-intensity sports, dance, or other forms of exercise has the same adverse effect on bones as the menopause. BMD in amen- orrheic athletes has been measured at levels 25% to 40% below control levels. When menses were resumed in these athletes, bone mass increased, but eventually plateaued at a level lower than that of sedentary women. Young women with the "female athlete triad" of disordered eating, amenorrhea, and low BMD are at increased risk for hav-