NASHVILLE, TENN. — Trabecular bone loss in both men and women may begin much earlier than previously thought, Dr. B. Lawrence Riggs reported at the annual meeting of the American Society for Bone and Mineral Research.
With his colleagues, Dr. Riggs of the Mayo Clinic College of Medicine in Rochester, Minn., used high-resolution peripheral quantitative CT (pQCT) to assess cortical and trabecular bone loss in 375 women and 325 men aged 21–97 years.
A total of 97 women were excluded from the analysis because they were receiving hormone replacement therapy, selective estrogen receptor modulators, or bisphosphonate therapy. Measurements of cortical and trabecular volumetric bone mineral density at the distal radius and the distal tibia were made at two to four consecutive annual visits.
In women, trabecular “bone loss appears to begin in young adulthood, probably in the third decade, and continues throughout life, with the suggestion of a menopausal acceleration at the distal radius,” said Dr. Riggs. Cortical bone loss does not really begin until menopause.
Premenopausal women lost an average of 0.67% of trabecular bone per year at the distal radius, compared with postmenopausal women, who lost 1% of trabecular bone per year. At the distal tibia, premenopausal women lost 0.53% trabecular bone per year, compared with 0.61% trabecular bone loss for postmenopausal women.
Cortical bone loss at the proximal radius was 0.11% per year for premenopausal women, compared with 0.60% for postmenopausal women. Cortical bone loss at the proximal tibia was 0.08% per year for premenopausal women and 0.57% per year for postmenopausal women.
In men “there really is no [cortical] bone loss until the age of 70,” said Dr. Riggs. Studies have shown that sex steroids begin to decline in men around this age. “Now with respect to trabecular bone loss in men, as in women, we do in fact see substantial trabecular bone loss … with more bone loss in young men than subsequently [thought],” said Dr. Riggs. This perhaps relates to changes in microstructure, he speculated.
Trabecular bone loss at the distal radius was 0.66% per year for men younger than age 50, compared with 0.53% for men aged 50 and older. Trabecular bone loss at the distal tibia was 0.68% per year for men younger than age 50 and 0.24% per year for men aged 50 and older.
Cortical bone loss at the proximal radius was 0.08% per year for men younger than 50 years, compared with 0.38% for men aged 50 and older. Cortical bone loss at the proximal tibia was 0.8% per year for men younger than 50 years and 0.22% per year for men aged 50 and older.
The early trabecular bone loss described accounts for a substantial proportion of total bone loss. “Consequently, determining the causation should be an important priority for future osteoporosis research,” said Dr. Riggs.
“The onset of substantial trabecular bone loss in both sexes soon after the conclusion of puberty and at a time when sex steroid levels are, by definition, normal indicates the current paradigms for the pathogenesis of osteoporosis are incomplete,” he said.