BONE MASS CHANGES

Normal bone		Osteoporotic bone

Scanning electron microscope photographs of normal and osteoporotic bone are shown here.³ Note the thin trabeculae, plate perforation, and loss of trabecular connectivity in the osteoporotic bone. 

Bone Mass Changes with Age in Females

The graph shown here demonstrates the changes in bone mass that occur throughout an individual's lifetime. ⁴ Peak bone mass is achieved in the mid-to-late twenties. At about age 35, an imbalance in bone turnover leads to the beginning of a gradual loss of bone (approximately 0.5 to 1 percent per year) in both men and women.⁵ With the onset of menopause, bone loss accelerates dramatically (especially trabecular bone) as a result of estrogen deficiency.⁵ In the menopausal and immediate postmenopausal years, approximately 2 to 4 percent of bone is lost per year.⁶ The reason for this increased rate of loss is not well-elucidated, but it may be due to changes in homeostasis or hormonal modulation of bone turnover. ⁷ There is no corresponding acceleration in bone loss seen in men. However, testicular function does decline somewhat with age and may contribute to age-related bone loss in males. After age 55 to 60, bone loss again slows to premenopausal rates.

The reasons for age-related bone loss are complex and poorly understood, and are probably influenced by gonadal hormone status, calcium intake and bioavailability, vitamin D status, physical activity, and hormones such as parathyroid hormone, corticosteroids, thyroid hormone, growth hormone, and calcitonin.⁶

Women lose approximately 50 percent of their trabecular bone and 30 percent of their cortical bone over the course of a lifetime; men lose approximately 30 percent and 20 percent, respectively. Trabecular bone is concentrated in the spinal column and at the end of long bones, and is where osteoporotic fractures occur most frequently.⁸

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